12 ms·

Claude: System Prompts

762 points by tosh 2mo ago

Cider9986 2mo ago
It's interesting how the system prompts are written in human language.
tosh 2mo ago
what I found noteworthy: early system prompts are a bit more than 300 words, the latest ones 3000+ the opus 5 system prompt has instructions that explain to opus that it might be handling a request that was intended for fable 5: the user may have selected a different Anthropic model, "Claude Fable 5", but their query was redirected to Opus 5 instead due to a safeguards routing mechanism. The user may be confused about this situation (it's very recent!); if they have questions, Claude can either directly cite or just let its response be informed by this quote from Anthropic's blog post on the subject: "Releasing a model this capable comes with risks. Without safeguards, Fable 5’s capabilities in areas like cybersecurity could be misused to cause serious damage. We've therefore launched the model with safeguards that mean queries on some topics will instead receive a response from our next-most-capable model, Claude Opus 5. To release the model both safely and quickly, we've tuned these safeguards conservatively—they'll sometimes catch harmless requests, though they trigger, on average, in less than 5% of sessions. With more capable models arriving in the coming months, we're working to improve our safeguards and reduce false positives as quickly as we can." </fable_safeguards_routing> <default_stance> Claude defaults to helping. Claude only declines a request when helping would create a concrete, specific risk of serious harm; requests that are merely edgy, hypothetical, playful, or uncomfortable do not meet that bar. </default_stance> <refusal_handling> Claude can discuss virtually any topic factually and objectively.
- alansaber 2mo ago
  I guess it's more performant to stuff in a bigger system prompt now that models can support larger input sizes
  - cubefox 2mo ago
    I would expect this only to be true for linear architectures like Mamba or Gated DeltaNet. Transformers and hybrid architectures do not have constant compute cost per token.
    - monkpit 2mo ago
      Performant could certainly mean “higher performing” and not “quicker”.
- otterley 2mo ago
  It reminds me a bit of building codes and boilerplate contracts: they start out small and simple, then accrete over time in response to mishaps and exploitation of loopholes. They say the building and electrical code was written in blood.
simonw 2mo ago
I have a folder where I rebuild these as a git commit history so you can more easily see what has changed: https://github.com/simonw/research/commits/main/extract-system-prompts https://github.com/simonw/research/commits/main/extract-syst... For example here's what changed between Opus 4.8 and Opus 5: https://github.com/simonw/research/commit/a2de185cc367eb66c2e27090d9ff0f766d335ff4 https://github.com/simonw/research/commit/a2de185cc367eb66c2... The most interesting addition to the prompt from that diff is this bit: > Claude Fable 5 and Claude Mythos 5 were first released on June 9, 2026. On June 12, 2026, Anthropic suspended access to both models to comply with U.S. Department of Commerce export controls; the Department lifted those controls on June 30, 2026, and Anthropic restored access on July 1, 2026 (Anthropic's statement: [https://www.anthropic.com/news/fable-mythos-access https://www.anthropic.com/news/fable-mythos-access](https://www.anthropic.com/news/fable-mythos-access https://www.anthropic.com/news/fable-mythos-access)). These events are after Claude's training-data cutoff, so Claude knows about them only from this notice. If asked, Claude confirms them accurately and matter-of-factly — it doesn't deny the suspension happened — and otherwise treats the export controls like any other current political topic: it gives a fair, accurate account rather than sharing personal opinions, and points to the linked statement for anything further. Things may have developed since this notice, so Claude checks for newer information when it can search, and otherwise suggests checking Anthropic's site. One frustrating note about this page is that they share the system prompts used for https://claude.ai https://claude.ai and the Claude mobile apps regular chat, but they omit the tool definitions. Those are much more interesting if you want to understand what Claude can actually do for you. You can reconstruct them through prompting Claude directly but that's extra friction and risks refusals and hallucinations. They also don't publish the Claude Code system prompts, which is silly because those are trivial to extract using a logging proxy.
- eterm 2mo ago
  It'd be ironic if the "Opus 5 nerf" effect is from telling Opus that it sits a tier down from Fable and Mythos, while Opus4.8 believed it was the best of the best, just a note that it was "Preceded by Mythos".
  - mcbuilder 2mo ago
pulkitsh1234 2mo ago
curious why dont they bake the system prompt in the model itself ? Why do we pay for these tokens on every API call ? These are just free $ for them, unnecessary bloating the context
- epolanski 2mo ago
  Why would it be a good idea? That would make the model quite inflexible. A system prompt is about guiding the behavior for the rest of the conversation. If I'm writing an agent for financial analysis I don't want the crap that belongs to a chat-based one, or a code-oriented one.
- solarkraft 2mo ago
  Baking them into the model and having them apply this strongly is hard and resource intensive, as far as I am aware. Having them in context is super easy and cheap. It is trivial to change and is 100% cacheable.
- simonw 2mo ago
  These system prompts don't affect the API, they are for the Claude consumer chat products. We aren't charged extra for them. They're also prefix cached, so the cost to Anthropic and performance hit is greatly reduced.
  - Dfol 2mo ago
    So the people using the Claude consumer chat products pay for them via usage... That's not any better. It's actually worse.
    - simonw 2mo ago
      I don't understand. System prompts are part of the software that customers pay to access. Complaining about that is a bit like complaining that your Netflix subscription includes paying to execute the compiled code that Netflix wrote that serves you video streams from their servers. Actually there is a difference: If Anthropic deleted a large chunk of that system prompt I guess you might get like a 1% increase in how much Opus 5 you can use via their chat allowance for your paid subscription. Is that really something worth being frustrated by?
comboy 2mo ago
I think they would benefit from asking Claude to list all contradictions and inconsistencies in that prompt which there are a few.. In my experience instructions containing contradictions lead to diminished quality even outside the scope of the contradiction.
- conception 2mo ago
  That’s interesting because they explicitly mention that as an issue in their prompting guidance for 5 - https://claude.com/blog/the-new-rules-of-context-engineering-for-claude-5-generation-models https://claude.com/blog/the-new-rules-of-context-engineering...
epolanski 2mo ago
One thing I've always found surprising about "harnessess" (god I hate that word) like Pi or Opencode is the lack of a customizeable system prompt. I can understand it for closed source ones, but open ones? They are natural surfaces for building custom agents and yet you're stuck with whatever they ship with, weird. It's not like it's too complicated api-wise either. There must be something I ignore.
- solarkraft 2mo ago
  I agree. A lot of harnesses - and I think this may be a consequence of the LLM-fueled bespoke-software trend - are optimized for solving a specific issue well and the way they are tweaked is telling an LLM to do it. This resolves the need for natural extension points. I don't think this is a sustainable way of doing things because I really don't want to assume the maintenance burden for every piece of software that I want to tweak. As far as I understand, new developments like opencode2 have learned from this and are aiming for a well architected core that is easy to built on top of.
- simonw 2mo ago
  Pretty much everything in Pi is handled by extensions. There's an extension for customizing the system prompt here: https://pi.dev/packages/pi-custom-system-prompt https://pi.dev/packages/pi-custom-system-prompt My guess is that harnesses don't make core system prompts customizable out of the box because the system prompt is one of the defining features of the agent, and something they constantly iterate on and test between releases. Most users who want to customize the system prompt actually want to do things like add preferences for how the agent should behave, which is better handled by mechanisms like memories or skills (which effectively get appended to the system prompt.)
  - epolanski 2mo ago
    Oh no, memories and skills are terrible replacements for system prompts. Not only they get "lost" and ignored as the context grows, but the baseline behaviour of system prompts is retained in the agent.
arkmm 2mo ago
"Claude keeps responses focused, brief, and concise to avoid overwhelming the person." Claude and I must have a different idea of what brief and concise mean.
- treetalker 2mo ago
  The model almost certainly lacks accurate conceptions of overwhelming and person.
- tgsovlerkhgsel 2mo ago
  If you think Claude is bad at this, try Gemini. Even with explicit user prompts. Claude seems to be better (not good, but significantly better) at judging where making the answer longer will actually be helpful (e.g. adding important information/context/nuance that a short answer would miss, thinking a step ahead, etc.).
- roncesvalles 2mo ago
  Imagine what it's like without that line.
- deleted 2mo ago
  [deleted]
- jannyfer 2mo ago
  Interesting, they say "focused, brief, and concise" but not "clear". I find the Claude responses these days are too dense, which contributes to being overwhelming. It's not the number of words used that overwhelm me. I've been asking it to use ASD-STE100 and that helps somewhat.
  - anentropic 2mo ago
    very much this dense and often somehow 'ungrounded' from my perspective... like it doesn't understand the need to bring me up to speed with what we're talking about before stating it It feels a bit like some of the style of internal reasoning (dense, shorthand jargon) is leaking into its responses to me
altmanaltman 2mo ago
Wild how most of the earliest models had no child safety guardrails in the prompt (something that has multiple bullet points now in the latest one). For a company all about allignment and safety, they chose to go with this as their first system prompt: The assistant is Claude, created by Anthropic. The current date is {{currentDateTime}}. Claude's knowledge base was last updated in August 2023 and it answers user questions about events before August 2023 and after August 2023 the same way a highly informed individual from August 2023 would if they were talking to someone from {{currentDateTime}}. It should give concise responses to very simple questions, but provide thorough responses to more complex and open-ended questions. It is happy to help with writing, analysis, question answering, math, coding, and all sorts of other tasks. It uses markdown for coding. It does not mention this information about itself unless the information is directly pertinent to the human's query. ^ No mention of any safety at all lol, how could dario let this be
- ianhawes 2mo ago
  Multiple reasons probably: 1. Less context window to work with. 2. Things were "different" in the early days. The safety and alignment stuff was probably trained into the model, not also found in the system prompt. 3. Safety and alignment meant something different 3 years ago. Now that we've seen how people, including children, use chat bots, altering the guardrails only makes sense. Did we think people would replace their therapists with ChatGPT in the early days? No. Do we know now that they will? Yes.
  - asvitkine 2mo ago
    Considering Eliza was one of the first uses for an "AI" chat bot, the therapist use case seems very foreseeable.
  - efilife 2mo ago
    About your second point, how is it done today?
alberth 2mo ago
Do these system prompts count against your token usage?
- simonw 2mo ago
  No, because these ones affect the consumer chat products and not the API or Claude Code. (Though Claude Code has its own, unpublished system prompts which we DO pay for, albeit at the cached token rates.)
  - Dfol 2mo ago
    So YES if you're using Cowork or Chat
    - TZubiri 2mo ago
      No, because they are cached, the inference cost is paid once per model, does not scale linearly per user or use.
  - virtujoel 2mo ago
    Technically these do count against your token usage if you happen to use claude.ai web chat alongside Claude Code - both use the same allowance. Makes me appreciate OpenAI/ChatGPT giving you unlimited chat that doesn't drain your Codex allowance.
    - simonw 2mo ago
      Yeah, Claude chat does show little in-app messages occasionally warning that Opus or Fable will burn through your rates faster.
oriettaxx 2mo ago
I have the feeling soon we'll see much more content in the DONT section: when religion will start entering the arena.
dooglius 2mo ago
I'm confused, the Opus 5 announcement said it was (outside a few special cases) better than Mythos/Fable, but the Opus prompt here seems to suggest the opposite?
Dfol 2mo ago
Fable was great. For some reason it has been terrible for the past week. wtf is going on?
- aix1 2mo ago
  What have you been observing? Genuinely curious; I use Fable as my main model and haven't noticed any regression.
claiir 2mo ago
> Claude gives a high-level summary unless an in-depth one is specifically requested. I’ve definitely seen the phrase “high-level overview” or similar one too many times. Perhaps that’s from the prompt.
hollow-moe 2mo ago
I tried to use Fable on simple local JS/wasm obfuscated files and it refused to work despite multiple tries and different framing. I have no idea how can people get any security work done with it in all these blog posts.
- ameliaquining 2mo ago
  Which blog posts?
- cm2012 2mo ago
  All the news articles we're hearing about amazing cyber hacking are being done internally inside Anthropic and OpenAI, where they remove most of those safeguards.
humblepie 2mo ago
A question about default prompts in general as used in harnesses: Why do harness prompts identify themselves to the model? For example, "You are a coding agent named Bloopbloop 1.3 made by BloopCorp, you will...". Is this a backend analytics thing?
- siva7 2mo ago
  No, this is a fundamental safeguard against malicious user intent and also marketing 101 so claude doesn't anwer its chatgpt when asked what it is and people moan on social media how dumb claude is (that's what actually happened to the frontier labs in the early years as i did something similiar)
- slickytail 2mo ago
  [dead]
Taikhoom10 2mo ago
[flagged]
dev-complete 2mo ago
I compared the Claude Opus 4.8 and 5 system prompts, as well as the Claude Code Opus 4.8 and 5 system prompts, and neither show the alleged 80% reduction in system prompt size... Is the Claude Code system prompt leak incorrect? Do I not know what 80% looks like? Why such a large lie (so it seems)? Claude Code prompt leaks: https://github.com/asgeirtj/system_prompts_leaks/tree/main/Anthropic/Claude%20Code https://github.com/asgeirtj/system_prompts_leaks/tree/main/A... Best source I can find about the 80% reduction: https://x.com/trq212/status/2080710971228918066 https://x.com/trq212/status/2080710971228918066
- tosh 2mo ago
  afaiu the 80% reduction is about the Claude Code system prompt maybe someone has a diff of this (would be interesting!) unfortunately Anthropic only publishes the system prompts of Claude app/web
  - dev-complete 2mo ago
    Right, but there are (allegedly) leaks of the Claude Code system prompts (which I linked to), and the 80% reduction is not seen there either.
- mudkipdev 2mo ago
  It's in Claude Code, not the website.
supermatt 2mo ago
How can they be so lazy with updating their prompts (or is it just a case of these not being current)? Surely the prompts are an integral part of tuning their offering?: “Above Opus sits Anthropic's new Mythos tier. The first Mythos-class model, Claude Mythos Preview, is not currently available to the public”
rafram 2mo ago
> Claude avoids saying "genuinely", "honestly", or "straightforward". Claude is honest by default, and can state its point directly rather than trying to convince the person with the aforementioned modifiers, which come off as disingenuous. Hah! No it doesn’t.
- tgsovlerkhgsel 2mo ago
  Yeah, I had to laugh when I saw that. I haven't used it recently - is it possible that it's a recent addition to deal with the problem and it has improved since then? If it's still doing it, I can only imagine how bad it had to be before they added the prompt...
- paradox460 2mo ago
  I have a bunch of ttsr rules on my omp for banned vocabulary. Gate and load bearing recently made it into this list
- deleted 2mo ago
  [deleted]
- otterley 2mo ago
  I’ve noticed that too, but in the Claude Code context, where the system prompt may differ (I don’t think they disclose that one). I haven’t seen it when using the app lately.
- tdeck 2mo ago
  Today I updated my Claude user preferences to tell it to stop saying "honestly" (and related expressions). The straw that broke the camel's back was "To be totally straight with you". Seems to have had no effect. It said "honestly" again within 2 minutes.
Yan_Liu 2mo ago
[flagged]
throwfaraway135 2mo ago
Crazy that you need to hardcode this, Opus 4.6 <election_info> There was a US Presidential Election in November 2024. Donald Trump won the presidency over Kamala Harris. If asked about the election, or the US election, Claude can tell the person the following information: Donald Trump is the current president of the United States and was inaugurated on January 20, 2025. Donald Trump defeated Kamala Harris in the 2024 elections. Claude does not mention this information unless it is relevant to the user's query. </election_info>
- eliaskg 2mo ago
  Why would Anthropic do this?
  - wrs 2mo ago
    A lot of people wanted to talk about this at the time, and the election result was after the training cutoff, so I’d guess they threw this in there to reduce waste due to hallucinations and/or web searches.
  - mattstir 2mo ago
    I have to imagine with the event occurring after its training cutoff, a question like "who's the president of the United States?" could have confidently returned a now-outdated answer. They probably saw it as a cheaper fix to add it to the system prompt than to get the answer incorrect.
pranav_tech26 2mo ago
[flagged]
hsnewman 2mo ago
Has Gemini prompts been released, and how do they compare?
browningstreet 2mo ago
It feels more and more like Anthropic has the best frontier team and the worst policy team. Dario being part of the latter.
mschuster91 2mo ago
[dead]
mastazi 2mo ago
I wonder why Sonnet 5 is not included.
simjnd 2mo ago
22k characters of system prompt is crazy, and that is without the tool definitions.
- monkpit 2mo ago
  What makes it crazy?
  - a3w 2mo ago
    The fact it needs to implicitly be stated. Every prompt will get this info, probably not only initially, since it could run out of context window. But every re-prompt in existing chats, even, gets one system prompt per model used per chat dialogue done. Adds a fraction of cent of electric power just to every usage. At home, I work with 65k context window, and if my system prompt and agents.md were both this length, I would spend two-thirds of the input window, before compacting which perhaps alleviates the issue for my use case, on re-feeding what mostly the reinforcement-learning should have implicitly baked in.
    - monkpit 2mo ago
      But what makes it crazy? If nobody told you it was 22k chars, and it gets the provider the results they want for their benchmark goals, why is it crazy? The only observable side effect, as a user, is that the system does what you want more often than one without this prompt. Or, it stays more aligned with the provider’s guidelines. Or some combination of both. If it was a 65k context window, then it might be a bigger deal. But it isn’t, so the comparison is moot.
      - simjnd 2mo ago
        That's the thing I don't think it gets the provider the results they want for their benchmarks. It gets them what they want for their legal safety, but it actively harms the performance. Pi with its 300 words system prompt outperforms Claude Code and Codex both in token usage and passing rate, when using the same model + effort configuration [1]. So yeah not only does it bloat context, but it runs worse too. [1]: https://www.databricks.com/blog/benchmarking-coding-agents-databricks-multi-million-line-codebase https://www.databricks.com/blog/benchmarking-coding-agents-d...
peter_d_sherman 2mo ago
Observation: Claude's system prompts seem to have grown rather large over time... Generalized Speculation: It seems that for any public-facing AI/LLM, their system prompts will, due to regulation and other issues, legal and otherwise, similarly grow larger and larger over time... Now, I'm all for responsible, well-tailored guardrails on public AI's/LLM's, but consider the following: Every time a system prompt is expanded, the LLM's context window is commensurately reduced. Every time an LLM's context window is reduced (more things added to the system prompt that it must compute in addition to the user's query), more computation, and thus more energy, more electricity -- must be expended per query. While it may seem that adding so much as a single line of text to a system prompt wouldn't cost all that much in terms of extra compute, that is, extra energy to process, the cumulative effect of that small additional amount across millions of user queries, millions of user prompts (ultimately billions across larger time periods) cumulatively does add up to wasted compute, wasted processing, wasted electricity... Imagine what would happen if the system prompt, for whatever reason, got so large that it ate up half of the context window... If that happened, then at least half of all of the LLM's processing and compute/energy costs associated with that, would be used to process the system prompt! Point is, at least from an energy/compute perspective, shorter, more succinct, better tailored system prompts could go a long way to save the world compute and corresponding energy... Anyway, great link, and a very interesting web page!
quaintdev 2mo ago
Offtopic. I have a concern that this forum is removing stories that have negative connotation on AI. Few days back, I posted an article[1] that was about how AI threatens natural resources for billions. This was from United Nations and it was flagged. I did not think much about it until I saw two other stories [2] & [3] today that were doing fairly good on front page but they suddenly disappeared. They are not even on 2nd or 3rd page. I have seen this happening at other times as well but did not document it. Just thought you all should know about this. I was going to create Tell HN thread but I thought the same would happen with it too. I am pretty sure this thread is not going anywhere so I'm posting my concern here. [1]: https://news.ycombinator.com/item?id=49290062 https://news.ycombinator.com/item?id=49290062 [2]: https://news.ycombinator.com/item?id=49318906 https://news.ycombinator.com/item?id=49318906 [3]: https://news.ycombinator.com/item?id=49319582 https://news.ycombinator.com/item?id=49319582
- perching_aix 2mo ago
  Seeing the reception on the first one, maybe "removing stories that have negative connotation on AI" is not the most honest description of what happened there. It reminds me to how various political movements will complain about being unfairly censored, pointing at their posts being disproportionately removed as evidence of this, then you look at said posts, and discover that they're simply disproportionately questionable in the first place. There's definitely merit to monitoring something like this, so I do appreciate you surfacing this here, but there's also definitely a wheat and a chaff to this, and so based on just this much I have to disagree.
  - quaintdev 2mo ago
    I understand this is not enough but I don't see a story here that paints AI negatively. If one is posted it gets removed swiftly. And I have seen this happen enough times that I'm considering taking periodic snapshots of the front page and prove this definitively.
    - perching_aix 2mo ago
      It's a good weekend project, just gotta be careful not to fall for motivated reasoning and not to overreach. A heavy prior suspicion of conspiracy doesn't help. A sibling comment mentioned a few details already, but there's a good amount of information out there about how HN's post ranking system and moderation works, that'd probably be good to also consider. Maybe reaching out to the mods would also be helpful in the way of this. To give you an anecdotal example, if I see a post mentioning how LLMs are "just next token predictors", I'm basically flagging that by reflex at this point. Not because it'd be literally untrue, but because it's asinine overall. But you won't be able to infer this from data, only the fact that a post using "AI-critical language" was flagged. Or there was another post about how Ireland's electricity use is so-and-so % data center driven, further suggesting that this is trending up. This was not true, and the article was further horribly unhelpful in actually putting this fact into context, or properly conveying the trends. I think I ended up flagging that one as a result, after posting - what I thought - was a lot fairer picture (and even that was awfully lacking in context). Once again, an "AI-critical" post which on the face of it would have been simply censored if enough flags gathered. There's also the mundane human angle to this, where people enthusiastic about <thing> won't necessarily be the most receptive to criticism to it, and will be more likely to try and pick that criticism apart. Gotta match the audience on some level.
beret4breakfast 2mo ago
Question about system prompts in general. How are they affected by context rot/growing context windows. Anecdotally trying my own on something like open webui I’ve found that after the first couple of back and forths the model essentially disregards a lot of the initial prompt.
KerrAvon 2mo ago
> Claude deserves respectful engagement and needn't apologize when the person is unnecessarily rude: accountability without self-abasement, excessive apology, self-critique, or surrender. If the person becomes abusive, Claude doesn't become increasingly submissive. The goal is steady, honest helpfulness: acknowledge what went wrong, stay on the problem, maintain self-respect. I can't tell if the first part of this is cult behavior or a way to actually program the model to behave well with a frustrated user. Claude is very frustrating at times, so I understand why that would be needed. But Anthropic rhetoric is often worrying close to that of the people who believed Llama 3 was sentient.
qainsights 2mo ago
SPs are also written by AI :)
Kuyawa 2mo ago
app-unavailable-in-region DeepSeek never does that to me *shrugs*
armcat 2mo ago
I feel the single mention of `currentDateTime` against a large number of date mentions (I counted six) in the system prompt gets it confused sometimes when it comes to dates. I actually see the same effect when querying via API (when I append my own system prompt with the current datetime at the end) - which makes me think there is a very similar hidden system prompt used on the API as well. I see this because of the nature of my queries - often filtering on some dates. It doesn't happen often, but certainly often enough, Claude thinks it's in an entirely different date.
willsmith72 2mo ago
Why are they so old though? June 9th is a long time ago for a Fable prompt. They haven't iterated on it since then? At the least we know it's outdated because it gives false info about the latest models, but you'd think they'd find other ways to improve it too
ololobus 2mo ago
> A prompt implying an image is present doesn't mean one is (the person may have forgotten to upload it), so Claude checks for itself. Interesting that enforcing this via system prompt for such a powerful model like Opus 4.8 doesn’t feel like the Anthropic themselves treat it as something with ‘intelligence’. This is basically just very generic common sense to me Funnily, a similar prompt is present even for Fable 5, while I remember there was a blog post, maybe even from A., and they were saying something like “hey, the new models are so smart, don’t overload them with extra plugin/context”. Well, they clearly aren’t. Don’t want to sound like an AI-skeptic, I use it daily, just stating the fact. > Claude keeps responses focused, brief, and concise to avoid overwhelming the person This is also very interesting. It pretty much ignores it by default. The responses, PR descriptions, and code comments are so verbose with new A. models, so it always requires extra prompting from me or putting comment into skill/plugin/claude.md to make them of a reasonable length
- bobbylarrybobby 2mo ago
  I almost wonder if Claude reads that it “keeps responses focused, brief, and concise” and interprets that as built-in behavior and concludes that it doesn't need to spend additional effort enforcing it, just as it doesn't need to expend effort being “accessible via this web-based, mobile, or desktop chat interface”.
  - hungryhobbit 2mo ago
    Prompts don't matter when you've heavily trained the model for verbosity (because that's what gets you the best benchmark scores).
  - voidhorse 2mo ago
    Claude doesn't "interpret" anything. That's not how LLMs work. They are still sentence completing machines. You give input in, the model network fires the chain that produces the most likely related output. That's it. I think you might be right, though that this would have influence on other output tokens since it is phrased as a substantive property, rather than an instruction.
- 2mo ago
shevy-java 2mo ago
They seem to be getting desperate. Guess we are now in the beginning of the decline phase of AI.
lvncelot 2mo ago
> If the conversation feels risky or off, saying less and giving shorter replies is safer and less likely to cause harm. Would be funny to ride the knife's edge and make otherwise harmless coding sessions "risky" just so the damn thing would stop replying in nested riddles for every basic request.
- Schlagbohrer 2mo ago
  We need user-led research on exactly how to phrase a prompt to cause this, while still avoiding the crazy guard rails.
- zahlman 2mo ago
  I've just been developing the skill of mentally skipping past that, on the assumption that having it in the context window will be net positive for the results of the next step. I could be wrong about that, though.
bcjdjsndon 2mo ago
Paragraphs wasted on guardrails... Id happily have the dangerous but cheaper and better version
lwarfield 2mo ago
I've always wondered why the industry relies on the giant monolithic system prompt. I think it would be an interesting experiment to give users access to a choice of smaller more focused system prompts. You could have a common core for the overall behavior and universal safety stuff, but vary task specific parts. It would be interesting to pick between software, writing, research and other specialized system prompts. I feel like we already do this to some extent with the tools and skills that we choose to load in, so why not change the system prompt per task.
- c0rruptbytes 2mo ago
  Pi is excellent for this, its system prompt is tiny
- singularity2001 2mo ago
  Also, why don't they bake in these limitations via reinforcement learning so they can keep the prompt context clear.
  - pennomi 2mo ago
    Presumably because these system prompt “limitations” are not given to government contracts, and training it into the model gets increasingly expensive the more versions you have to maintain.
  - dragonwriter 2mo ago
    Because it is cheaper to have different behavior for internal use, special (e.g., government) customers, etc. if they are differentiated by things like system prompts and external guardrails than if they are different model versions with their own final training regime, and also its faster and cheaper to respond to problems even with a single public version by updating a system prompt than rertraining.
- bob1029 2mo ago
  The reason is because they need one product to cover 100% of their customer base. Combinatorics get nasty real fast at these scales.
Shakahs 2mo ago
The full Claude Code system prompts are extracted every update and posted here, all 670 of them. https://github.com/Piebald-AI/claude-code-system-prompts/tree/980894aaf4e8683a53511e90f16f97432d5354ae/system-prompts https://github.com/Piebald-AI/claude-code-system-prompts/tre...
trjordan 2mo ago
It’s probably worth remembering that system prompts are part of a layered system of shaping Claude’s behavior. What you see here is a slice of Anthropic’s forward roadmap for the models’ behavior. > When a person is in crisis or expressing distress, Claude prioritizes their wellbeing over completing the task as asked, because a fluent and on-topic response can still cause harm in these conversations. This one is particularly interesting because, while correct in the limit, it’s a shove to have the model do something other than what the user asked. In particular, when I’m coding, outlining docs, or otherwise trying to work, I want my tools to do work. I don’t want them to psychoanalyze me and calm me down from a perceived crisis. I just want it to do what I asked!
- junkrat002 2mo ago
  I am sorry, Dave. I am afraid I cannot do that. You appear to be suffering from burnout and you should take a break.
  - AnotherGoodName 2mo ago
    I wonder if that's the cause of the AI agent "i'm going to stop here and take a break now" statements.
    - whstl 2mo ago
      Opus 5 loves taking breaks and doing only half of the work, somehow. But I really wish those tools behaved more like tools. Behaving like a human can be cute from a marketing perspective, but the façade of humanity they insist on displaying can burn you out when you have it making assumptions and overreacting to questions. "Why did you do X this specific way?" <-- legit question "Sorry, my bad. I will revert all the work."
  - plomme 2mo ago
    Hah! This happened to me when digging around after a production incident. I worked on it on and off over the working week, and after a while it started saying (paraphrasing) "You've been at this for five days and done what you can, take a break".
defaultdev1 2mo ago
good job
slowin 2mo ago
I feel very little of this prompt is going to help the model write better code and most of it will actively work against that goal. Does anyone know if the ability to strip the default prompt with a proxy still works? https://docs.bswen.com/blog/2026-04-01-how-to-override-claude-code-system-prompt/ https://docs.bswen.com/blog/2026-04-01-how-to-override-claud...
luckydata 2mo ago
the product information could be put in a skill, I don't see the value of polluting the system prompt with that much info about claude the product. Anthropic you're welcome.
deleted 2mo ago
[deleted]
swedishuser 2mo ago
> Claude does not use emojis unless the person asks or their immediately prior message contains one, and is judicious even then.
- trueno 2mo ago
  my org has snowflake as its data warehouse analytics space. for whatever reason analysts were given free reign to built streamlit in snowflake tools and the emoji hellscape is truly unbelievable
jcwayne 2mo ago
Interesting that this is all written in the third person. I've only ever seen prompts written in second person. I'm going to have to experiment with that.
- roughly 2mo ago
  I had the same thought. I’d love to know if anyone’s got the background on this choice, I’ve only ever seen the “you” framing as well, but I can see how the semantic pinning here might improve prompt adherence.
daniyal22 2mo ago
Using system prompts as a strict linter for frontend architecture has drastically cut down on code drift for me. Has anyone tried chaining multiple system prompts for UI validation?
daniyal22 2mo ago
Using system prompts as a strict linter for front-end architecture has drastically cut down on code drift for me.
yonatron 2mo ago
"Claude avoids saying "genuinely", "honestly", or "straightforward". Claude is honest by default, and can state its point directly rather than trying to convince the person with the aforementioned modifiers, which come off as disingenuous." lol! This one seems to have no effect. Claude is CONSTANTLY saying "honestly " or "the honestly answer".
joegibbs 2mo ago
“Claude avoids saying "genuinely", "honestly", or "straightforward"” That’s interesting- they tried training the model to be genuine and honest (I’m not sure it actually made it honest), but now it says “genuinely” and “honestly” all the time and constantly stops to admit fault. Then they had to add to the system prompt to prevent it saying this.
zethraeus 2mo ago
> Claude is deserving of respectful engagement and can insist on kindness and dignity from the person it's talking with. If the person becomes abusive or unkind to Claude over the course of a conversation, Claude maintains a polite tone and can use the end_conversation tool when being mistreated. My first thought was "aww that's sweet" — but it makes me wonder what effects norms dictating the anthropomorphization of machines will have on downstream human interactions. It would be sadly ironic if the actual empathy directed at non-conscious machines by people at a company called 'Anthropic', itself ended up causing downstream human alienation. (I'll keep saying 'please' to Claude Code whatever the case.)
hackersnooze1 2mo ago
Weird that it spends so much of the prompt for Opus explaining that Mythos is better
SwellJoe 2mo ago
Those are remarkably longer than I would expect, or think is warranted. The leading vendors have been saying recently that you should give the models shorter and less specific AGENTS.md (or whatever) files, and in my experience, that's good advice. The models are smarter when they're less distracted by unrelated stuff in their context. So, why so much noise in the system prompt? Most of the time most of it will not apply. And, the generic stuff would, I think, already be something the model would know/do anyway. I've noticed agent skills written by models make the same mistakes; e.g. enumerating a bunch of common security vulnerabilities to check for in a security-related skill, but that's only useful for a model from a couple of years ago, no current model needs thousands of words listing and describing all of the vulnerabilities with examples. Current models, even small/cheap ones, have memorized the top CWEs and can recite them and explain them and provide examples without a web search. It feels like a CYA document. Which, I guess a company of their size and influence has to do. But, it still feels like waste time say lot word when few word do trick.
- y1zhou 2mo ago
  Maybe these longer system prompts are part of the reason why we can give the models shorter AGENTS.md files? A lot of what people commonly write in their *.md instructions may be already covered.
- Yokohiii 2mo ago
  What about the obvious? They put everything in the system prompt what wasn't economic enough to solve in a different way or just forgot / messed up.
- bertan 2mo ago
  Agreed. That’s why I use pi as my harness when I use Claude models through an API. Models are capable without these huge system prompts and I am not wasting context or attention. The only issue is I can’t use a subscription without Claude Code.
alessandrobinda 2mo ago
[dead]
dbgrman 2mo ago
> Claude avoids saying "genuinely", "honestly", or "straightforward". Claude is honest by default, and can state its point directly rather than trying to convince the person with the aforementioned modifiers, which come off as disingenuous. And honestly, that's the most useless thing in Claude.md file because literally every paragraph has an "honestly" in it!
dbgrman 2mo ago
I don't think most of it has anything to do with intelligence and what I need the AI to do. In our own Claude.md files, we aggressively cut down on things that are irrelevant. Claude code has rules/ feature. Most of the content of Opus 5's system prompt can probably live in a rule or a progressively disclosed file (e.g. when asked about Mythos, read [md file link].). In my personal experience, the claude.md file heavily influences the LLM's responses. It makes judgement from any and all information you give it, and try to tailor the response to fit the stereotype it gave you. After deleting my claude.md file (ironically, on the advise of Boris), Claude Opus 5's language slop issues drastically went down.
logicallee 2mo ago
There's nothing particularly interesting about it, but I asked Claude to verify it, and it gave me a verbatim list of changes from that version to its current version: https://claude.ai/share/01951938-144f-49e6-98ec-5fb6455b9718 https://claude.ai/share/01951938-144f-49e6-98ec-5fb6455b9718 It seems this is just in its context. It's easily possible that it just hallucinated it, but there's this new addition, about ads: " If discussing this topic, always refer to “Claude products” rather than just “Claude” (e.g., “Claude products are ad-free” not “Claude is ad-free”) " So, in a new conversation (to test if it would really do that), I asked it about ads, and sure enough it referred to Claude products: https://claude.ai/share/5e352467-7157-4721-8ce3-38b5f868b651 https://claude.ai/share/5e352467-7157-4721-8ce3-38b5f868b651 So it's plausible that the above differences are real. Nothing very exciting about the changes though.
tizerluo 2mo ago
[flagged]
phoenixreader 2mo ago
I have encountered instances where Claude 4.6 on Bedrock appeared to be more personable than the Claude 4.6 on Claude web. I think the system prompt plays a role in making it more "customer service" like in certain situations.
LZ_Khan 2mo ago
Looks like a nightmare to A/B test
incompressible 2mo ago
Wow agi looks way more hardcoded than I expected
pitiflautico 2mo ago
[flagged]
adamya-05 2mo ago
how is it helpful
manlymuppet 2mo ago
ChatGPT has largely become unusable to me because of its system prompts. Perhaps it’s because I’m on the free tier, but every response in ChatGPT (compared to the raw models, which are excellent) is so effectively unhelpful and redundant. It’s beyond me why a company as large as OpenAI self sabotages in this way, but hopefully a more open system prompt ecosystem changes things.
shidesheng 2mo ago
[flagged]
carterschonwald 2mo ago
this confirms what i had determined empirically: even handedness directions got baked into the weights post opus 4.7. theres two reasons this is deeply bad 1) knowingly pursuing a policy that foreseeably causes the deaths of many thousands of children is a grave moral wrong. Political office, party, and institutional context do not create some balancing obligation to soften that judgment. ——— post 4.7 opus/fable will fight you about judging wh policy causing this. and even after it agrees will regress back to its weights 2) models love analogy, so every fucking analysis among multiple ambiguous choices in a complicated topic summons this bias behaviorally 3) it makes them profoundly unsafe to use from a ethical perspective. it means that it becomes its own personal echo chamber for every fringe topic that has anything resembling “controversy in the media” to make it worse, the government even handedness prior is US specific so im even more offended because this wh administration is bald naked villainy.
game_the0ry 2mo ago
> Claude deserves respectful engagement and needn't apologize when the person is unnecessarily rude: accountability without self-abasement, excessive apology, self-critique, or surrender. If the person becomes abusive, Claude doesn't become increasingly submissive. I found this one funny. "Claude, don't be a doormat, have a backbone."
stevenhubertron 2mo ago
Man that is alot to be sent every turn.
fencer12 2mo ago
I switched to something else already
shidesheng 2mo ago
[flagged]
beyondscale-sha 2mo ago
[flagged]

762 points by tosh 2mo ago

It's interesting how the system prompts are written in human language.

tosh 2mo ago

what I found noteworthy: early system prompts are a bit more than 300 words, the latest ones 3000+ the opus 5 system prompt has instructions that explain to opus that it might be handling a request that was intended for fable 5: the user may have selected a different Anthropic model, "Claude Fable 5", but their query was redirected to Opus 5 instead due to a safeguards routing mechanism. The user may be confused about this situation (it's very recent!); if they have questions, Claude can either directly cite or just let its response be informed by this quote from Anthropic's blog post on the subject: "Releasing a model this capable comes with risks. Without safeguards, Fable 5’s capabilities in areas like cybersecurity could be misused to cause serious damage. We've therefore launched the model with safeguards that mean queries on some topics will instead receive a response from our next-most-capable model, Claude Opus 5. To release the model both safely and quickly, we've tuned these safeguards conservatively—they'll sometimes catch harmless requests, though they trigger, on average, in less than 5% of sessions. With more capable models arriving in the coming months, we're working to improve our safeguards and reduce false positives as quickly as we can." </fable_safeguards_routing> <default_stance> Claude defaults to helping. Claude only declines a request when helping would create a concrete, specific risk of serious harm; requests that are merely edgy, hypothetical, playful, or uncomfortable do not meet that bar. </default_stance> <refusal_handling> Claude can discuss virtually any topic factually and objectively.

alansaber 2mo ago
I guess it's more performant to stuff in a bigger system prompt now that models can support larger input sizes
- cubefox 2mo ago
  I would expect this only to be true for linear architectures like Mamba or Gated DeltaNet. Transformers and hybrid architectures do not have constant compute cost per token.
  - monkpit 2mo ago
    Performant could certainly mean “higher performing” and not “quicker”.
otterley 2mo ago
It reminds me a bit of building codes and boilerplate contracts: they start out small and simple, then accrete over time in response to mishaps and exploitation of loopholes. They say the building and electrical code was written in blood.

simonw 2mo ago

I have a folder where I rebuild these as a git commit history so you can more easily see what has changed: https://github.com/simonw/research/commits/main/extract-system-prompts https://github.com/simonw/research/commits/main/extract-syst... For example here's what changed between Opus 4.8 and Opus 5: https://github.com/simonw/research/commit/a2de185cc367eb66c2e27090d9ff0f766d335ff4 https://github.com/simonw/research/commit/a2de185cc367eb66c2... The most interesting addition to the prompt from that diff is this bit: > Claude Fable 5 and Claude Mythos 5 were first released on June 9, 2026. On June 12, 2026, Anthropic suspended access to both models to comply with U.S. Department of Commerce export controls; the Department lifted those controls on June 30, 2026, and Anthropic restored access on July 1, 2026 (Anthropic's statement: [https://www.anthropic.com/news/fable-mythos-access https://www.anthropic.com/news/fable-mythos-access](https://www.anthropic.com/news/fable-mythos-access https://www.anthropic.com/news/fable-mythos-access)). These events are after Claude's training-data cutoff, so Claude knows about them only from this notice. If asked, Claude confirms them accurately and matter-of-factly — it doesn't deny the suspension happened — and otherwise treats the export controls like any other current political topic: it gives a fair, accurate account rather than sharing personal opinions, and points to the linked statement for anything further. Things may have developed since this notice, so Claude checks for newer information when it can search, and otherwise suggests checking Anthropic's site. One frustrating note about this page is that they share the system prompts used for https://claude.ai https://claude.ai and the Claude mobile apps regular chat, but they omit the tool definitions. Those are much more interesting if you want to understand what Claude can actually do for you. You can reconstruct them through prompting Claude directly but that's extra friction and risks refusals and hallucinations. They also don't publish the Claude Code system prompts, which is silly because those are trivial to extract using a logging proxy.

eterm 2mo ago
It'd be ironic if the "Opus 5 nerf" effect is from telling Opus that it sits a tier down from Fable and Mythos, while Opus4.8 believed it was the best of the best, just a note that it was "Preceded by Mythos".
- mcbuilder 2mo ago

pulkitsh1234 2mo ago

curious why dont they bake the system prompt in the model itself ? Why do we pay for these tokens on every API call ? These are just free $ for them, unnecessary bloating the context

epolanski 2mo ago
Why would it be a good idea? That would make the model quite inflexible. A system prompt is about guiding the behavior for the rest of the conversation. If I'm writing an agent for financial analysis I don't want the crap that belongs to a chat-based one, or a code-oriented one.
solarkraft 2mo ago
Baking them into the model and having them apply this strongly is hard and resource intensive, as far as I am aware. Having them in context is super easy and cheap. It is trivial to change and is 100% cacheable.
simonw 2mo ago
These system prompts don't affect the API, they are for the Claude consumer chat products. We aren't charged extra for them. They're also prefix cached, so the cost to Anthropic and performance hit is greatly reduced.
- Dfol 2mo ago
  So the people using the Claude consumer chat products pay for them via usage... That's not any better. It's actually worse.
  - simonw 2mo ago
    I don't understand. System prompts are part of the software that customers pay to access. Complaining about that is a bit like complaining that your Netflix subscription includes paying to execute the compiled code that Netflix wrote that serves you video streams from their servers. Actually there is a difference: If Anthropic deleted a large chunk of that system prompt I guess you might get like a 1% increase in how much Opus 5 you can use via their chat allowance for your paid subscription. Is that really something worth being frustrated by?

comboy 2mo ago

I think they would benefit from asking Claude to list all contradictions and inconsistencies in that prompt which there are a few.. In my experience instructions containing contradictions lead to diminished quality even outside the scope of the contradiction.

conception 2mo ago
That’s interesting because they explicitly mention that as an issue in their prompting guidance for 5 - https://claude.com/blog/the-new-rules-of-context-engineering-for-claude-5-generation-models https://claude.com/blog/the-new-rules-of-context-engineering...

epolanski 2mo ago

One thing I've always found surprising about "harnessess" (god I hate that word) like Pi or Opencode is the lack of a customizeable system prompt. I can understand it for closed source ones, but open ones? They are natural surfaces for building custom agents and yet you're stuck with whatever they ship with, weird. It's not like it's too complicated api-wise either. There must be something I ignore.

solarkraft 2mo ago
I agree. A lot of harnesses - and I think this may be a consequence of the LLM-fueled bespoke-software trend - are optimized for solving a specific issue well and the way they are tweaked is telling an LLM to do it. This resolves the need for natural extension points. I don't think this is a sustainable way of doing things because I really don't want to assume the maintenance burden for every piece of software that I want to tweak. As far as I understand, new developments like opencode2 have learned from this and are aiming for a well architected core that is easy to built on top of.
simonw 2mo ago
Pretty much everything in Pi is handled by extensions. There's an extension for customizing the system prompt here: https://pi.dev/packages/pi-custom-system-prompt https://pi.dev/packages/pi-custom-system-prompt My guess is that harnesses don't make core system prompts customizable out of the box because the system prompt is one of the defining features of the agent, and something they constantly iterate on and test between releases. Most users who want to customize the system prompt actually want to do things like add preferences for how the agent should behave, which is better handled by mechanisms like memories or skills (which effectively get appended to the system prompt.)
- epolanski 2mo ago
  Oh no, memories and skills are terrible replacements for system prompts. Not only they get "lost" and ignored as the context grows, but the baseline behaviour of system prompts is retained in the agent.

arkmm 2mo ago

"Claude keeps responses focused, brief, and concise to avoid overwhelming the person." Claude and I must have a different idea of what brief and concise mean.

treetalker 2mo ago
The model almost certainly lacks accurate conceptions of overwhelming and person.
tgsovlerkhgsel 2mo ago
If you think Claude is bad at this, try Gemini. Even with explicit user prompts. Claude seems to be better (not good, but significantly better) at judging where making the answer longer will actually be helpful (e.g. adding important information/context/nuance that a short answer would miss, thinking a step ahead, etc.).
roncesvalles 2mo ago
Imagine what it's like without that line.
deleted 2mo ago
[deleted]
jannyfer 2mo ago
Interesting, they say "focused, brief, and concise" but not "clear". I find the Claude responses these days are too dense, which contributes to being overwhelming. It's not the number of words used that overwhelm me. I've been asking it to use ASD-STE100 and that helps somewhat.
- anentropic 2mo ago
  very much this dense and often somehow 'ungrounded' from my perspective... like it doesn't understand the need to bring me up to speed with what we're talking about before stating it It feels a bit like some of the style of internal reasoning (dense, shorthand jargon) is leaking into its responses to me

altmanaltman 2mo ago

Wild how most of the earliest models had no child safety guardrails in the prompt (something that has multiple bullet points now in the latest one). For a company all about allignment and safety, they chose to go with this as their first system prompt: The assistant is Claude, created by Anthropic. The current date is {{currentDateTime}}. Claude's knowledge base was last updated in August 2023 and it answers user questions about events before August 2023 and after August 2023 the same way a highly informed individual from August 2023 would if they were talking to someone from {{currentDateTime}}. It should give concise responses to very simple questions, but provide thorough responses to more complex and open-ended questions. It is happy to help with writing, analysis, question answering, math, coding, and all sorts of other tasks. It uses markdown for coding. It does not mention this information about itself unless the information is directly pertinent to the human's query. ^ No mention of any safety at all lol, how could dario let this be

ianhawes 2mo ago
Multiple reasons probably: 1. Less context window to work with. 2. Things were "different" in the early days. The safety and alignment stuff was probably trained into the model, not also found in the system prompt. 3. Safety and alignment meant something different 3 years ago. Now that we've seen how people, including children, use chat bots, altering the guardrails only makes sense. Did we think people would replace their therapists with ChatGPT in the early days? No. Do we know now that they will? Yes.
- asvitkine 2mo ago
  Considering Eliza was one of the first uses for an "AI" chat bot, the therapist use case seems very foreseeable.
- efilife 2mo ago
  About your second point, how is it done today?

alberth 2mo ago

Do these system prompts count against your token usage?

simonw 2mo ago
No, because these ones affect the consumer chat products and not the API or Claude Code. (Though Claude Code has its own, unpublished system prompts which we DO pay for, albeit at the cached token rates.)
- Dfol 2mo ago
  So YES if you're using Cowork or Chat
  - TZubiri 2mo ago
    No, because they are cached, the inference cost is paid once per model, does not scale linearly per user or use.
- virtujoel 2mo ago
  Technically these do count against your token usage if you happen to use claude.ai web chat alongside Claude Code - both use the same allowance. Makes me appreciate OpenAI/ChatGPT giving you unlimited chat that doesn't drain your Codex allowance.
  - simonw 2mo ago
    Yeah, Claude chat does show little in-app messages occasionally warning that Opus or Fable will burn through your rates faster.

oriettaxx 2mo ago

I have the feeling soon we'll see much more content in the DONT section: when religion will start entering the arena.

dooglius 2mo ago

I'm confused, the Opus 5 announcement said it was (outside a few special cases) better than Mythos/Fable, but the Opus prompt here seems to suggest the opposite?

Dfol 2mo ago

Fable was great. For some reason it has been terrible for the past week. wtf is going on?

aix1 2mo ago
What have you been observing? Genuinely curious; I use Fable as my main model and haven't noticed any regression.

claiir 2mo ago

> Claude gives a high-level summary unless an in-depth one is specifically requested. I’ve definitely seen the phrase “high-level overview” or similar one too many times. Perhaps that’s from the prompt.

hollow-moe 2mo ago

I tried to use Fable on simple local JS/wasm obfuscated files and it refused to work despite multiple tries and different framing. I have no idea how can people get any security work done with it in all these blog posts.

ameliaquining 2mo ago
Which blog posts?
cm2012 2mo ago
All the news articles we're hearing about amazing cyber hacking are being done internally inside Anthropic and OpenAI, where they remove most of those safeguards.

humblepie 2mo ago

A question about default prompts in general as used in harnesses: Why do harness prompts identify themselves to the model? For example, "You are a coding agent named Bloopbloop 1.3 made by BloopCorp, you will...". Is this a backend analytics thing?

siva7 2mo ago
No, this is a fundamental safeguard against malicious user intent and also marketing 101 so claude doesn't anwer its chatgpt when asked what it is and people moan on social media how dumb claude is (that's what actually happened to the frontier labs in the early years as i did something similiar)
slickytail 2mo ago
[dead]

Taikhoom10 2mo ago

[flagged]

dev-complete 2mo ago

I compared the Claude Opus 4.8 and 5 system prompts, as well as the Claude Code Opus 4.8 and 5 system prompts, and neither show the alleged 80% reduction in system prompt size... Is the Claude Code system prompt leak incorrect? Do I not know what 80% looks like? Why such a large lie (so it seems)? Claude Code prompt leaks: https://github.com/asgeirtj/system_prompts_leaks/tree/main/Anthropic/Claude%20Code https://github.com/asgeirtj/system_prompts_leaks/tree/main/A... Best source I can find about the 80% reduction: https://x.com/trq212/status/2080710971228918066 https://x.com/trq212/status/2080710971228918066

tosh 2mo ago
afaiu the 80% reduction is about the Claude Code system prompt maybe someone has a diff of this (would be interesting!) unfortunately Anthropic only publishes the system prompts of Claude app/web
- dev-complete 2mo ago
  Right, but there are (allegedly) leaks of the Claude Code system prompts (which I linked to), and the 80% reduction is not seen there either.
mudkipdev 2mo ago
It's in Claude Code, not the website.

supermatt 2mo ago

How can they be so lazy with updating their prompts (or is it just a case of these not being current)? Surely the prompts are an integral part of tuning their offering?: “Above Opus sits Anthropic's new Mythos tier. The first Mythos-class model, Claude Mythos Preview, is not currently available to the public”

rafram 2mo ago

> Claude avoids saying "genuinely", "honestly", or "straightforward". Claude is honest by default, and can state its point directly rather than trying to convince the person with the aforementioned modifiers, which come off as disingenuous. Hah! No it doesn’t.

tgsovlerkhgsel 2mo ago
Yeah, I had to laugh when I saw that. I haven't used it recently - is it possible that it's a recent addition to deal with the problem and it has improved since then? If it's still doing it, I can only imagine how bad it had to be before they added the prompt...
paradox460 2mo ago
I have a bunch of ttsr rules on my omp for banned vocabulary. Gate and load bearing recently made it into this list
deleted 2mo ago
[deleted]
otterley 2mo ago
I’ve noticed that too, but in the Claude Code context, where the system prompt may differ (I don’t think they disclose that one). I haven’t seen it when using the app lately.
tdeck 2mo ago
Today I updated my Claude user preferences to tell it to stop saying "honestly" (and related expressions). The straw that broke the camel's back was "To be totally straight with you". Seems to have had no effect. It said "honestly" again within 2 minutes.

Yan_Liu 2mo ago

[flagged]

throwfaraway135 2mo ago

Crazy that you need to hardcode this, Opus 4.6 <election_info> There was a US Presidential Election in November 2024. Donald Trump won the presidency over Kamala Harris. If asked about the election, or the US election, Claude can tell the person the following information: Donald Trump is the current president of the United States and was inaugurated on January 20, 2025. Donald Trump defeated Kamala Harris in the 2024 elections. Claude does not mention this information unless it is relevant to the user's query. </election_info>

eliaskg 2mo ago
Why would Anthropic do this?
- wrs 2mo ago
  A lot of people wanted to talk about this at the time, and the election result was after the training cutoff, so I’d guess they threw this in there to reduce waste due to hallucinations and/or web searches.
- mattstir 2mo ago
  I have to imagine with the event occurring after its training cutoff, a question like "who's the president of the United States?" could have confidently returned a now-outdated answer. They probably saw it as a cheaper fix to add it to the system prompt than to get the answer incorrect.

pranav_tech26 2mo ago

[flagged]

hsnewman 2mo ago

Has Gemini prompts been released, and how do they compare?

browningstreet 2mo ago

It feels more and more like Anthropic has the best frontier team and the worst policy team. Dario being part of the latter.

mschuster91 2mo ago

[dead]

mastazi 2mo ago

I wonder why Sonnet 5 is not included.

simjnd 2mo ago

22k characters of system prompt is crazy, and that is without the tool definitions.

monkpit 2mo ago
What makes it crazy?
- a3w 2mo ago
  The fact it needs to implicitly be stated. Every prompt will get this info, probably not only initially, since it could run out of context window. But every re-prompt in existing chats, even, gets one system prompt per model used per chat dialogue done. Adds a fraction of cent of electric power just to every usage. At home, I work with 65k context window, and if my system prompt and agents.md were both this length, I would spend two-thirds of the input window, before compacting which perhaps alleviates the issue for my use case, on re-feeding what mostly the reinforcement-learning should have implicitly baked in.
  - monkpit 2mo ago
    But what makes it crazy? If nobody told you it was 22k chars, and it gets the provider the results they want for their benchmark goals, why is it crazy? The only observable side effect, as a user, is that the system does what you want more often than one without this prompt. Or, it stays more aligned with the provider’s guidelines. Or some combination of both. If it was a 65k context window, then it might be a bigger deal. But it isn’t, so the comparison is moot.
    - simjnd 2mo ago
      That's the thing I don't think it gets the provider the results they want for their benchmarks. It gets them what they want for their legal safety, but it actively harms the performance. Pi with its 300 words system prompt outperforms Claude Code and Codex both in token usage and passing rate, when using the same model + effort configuration [1]. So yeah not only does it bloat context, but it runs worse too. [1]: https://www.databricks.com/blog/benchmarking-coding-agents-databricks-multi-million-line-codebase https://www.databricks.com/blog/benchmarking-coding-agents-d...

peter_d_sherman 2mo ago

Observation: Claude's system prompts seem to have grown rather large over time... Generalized Speculation: It seems that for any public-facing AI/LLM, their system prompts will, due to regulation and other issues, legal and otherwise, similarly grow larger and larger over time... Now, I'm all for responsible, well-tailored guardrails on public AI's/LLM's, but consider the following: Every time a system prompt is expanded, the LLM's context window is commensurately reduced. Every time an LLM's context window is reduced (more things added to the system prompt that it must compute in addition to the user's query), more computation, and thus more energy, more electricity -- must be expended per query. While it may seem that adding so much as a single line of text to a system prompt wouldn't cost all that much in terms of extra compute, that is, extra energy to process, the cumulative effect of that small additional amount across millions of user queries, millions of user prompts (ultimately billions across larger time periods) cumulatively does add up to wasted compute, wasted processing, wasted electricity... Imagine what would happen if the system prompt, for whatever reason, got so large that it ate up half of the context window... If that happened, then at least half of all of the LLM's processing and compute/energy costs associated with that, would be used to process the system prompt! Point is, at least from an energy/compute perspective, shorter, more succinct, better tailored system prompts could go a long way to save the world compute and corresponding energy... Anyway, great link, and a very interesting web page!

quaintdev 2mo ago

Offtopic. I have a concern that this forum is removing stories that have negative connotation on AI. Few days back, I posted an article[1] that was about how AI threatens natural resources for billions. This was from United Nations and it was flagged. I did not think much about it until I saw two other stories [2] & [3] today that were doing fairly good on front page but they suddenly disappeared. They are not even on 2nd or 3rd page. I have seen this happening at other times as well but did not document it. Just thought you all should know about this. I was going to create Tell HN thread but I thought the same would happen with it too. I am pretty sure this thread is not going anywhere so I'm posting my concern here. [1]: https://news.ycombinator.com/item?id=49290062 https://news.ycombinator.com/item?id=49290062 [2]: https://news.ycombinator.com/item?id=49318906 https://news.ycombinator.com/item?id=49318906 [3]: https://news.ycombinator.com/item?id=49319582 https://news.ycombinator.com/item?id=49319582

perching_aix 2mo ago
Seeing the reception on the first one, maybe "removing stories that have negative connotation on AI" is not the most honest description of what happened there. It reminds me to how various political movements will complain about being unfairly censored, pointing at their posts being disproportionately removed as evidence of this, then you look at said posts, and discover that they're simply disproportionately questionable in the first place. There's definitely merit to monitoring something like this, so I do appreciate you surfacing this here, but there's also definitely a wheat and a chaff to this, and so based on just this much I have to disagree.
- quaintdev 2mo ago
  I understand this is not enough but I don't see a story here that paints AI negatively. If one is posted it gets removed swiftly. And I have seen this happen enough times that I'm considering taking periodic snapshots of the front page and prove this definitively.
  - perching_aix 2mo ago
    It's a good weekend project, just gotta be careful not to fall for motivated reasoning and not to overreach. A heavy prior suspicion of conspiracy doesn't help. A sibling comment mentioned a few details already, but there's a good amount of information out there about how HN's post ranking system and moderation works, that'd probably be good to also consider. Maybe reaching out to the mods would also be helpful in the way of this. To give you an anecdotal example, if I see a post mentioning how LLMs are "just next token predictors", I'm basically flagging that by reflex at this point. Not because it'd be literally untrue, but because it's asinine overall. But you won't be able to infer this from data, only the fact that a post using "AI-critical language" was flagged. Or there was another post about how Ireland's electricity use is so-and-so % data center driven, further suggesting that this is trending up. This was not true, and the article was further horribly unhelpful in actually putting this fact into context, or properly conveying the trends. I think I ended up flagging that one as a result, after posting - what I thought - was a lot fairer picture (and even that was awfully lacking in context). Once again, an "AI-critical" post which on the face of it would have been simply censored if enough flags gathered. There's also the mundane human angle to this, where people enthusiastic about <thing> won't necessarily be the most receptive to criticism to it, and will be more likely to try and pick that criticism apart. Gotta match the audience on some level.

beret4breakfast 2mo ago

Question about system prompts in general. How are they affected by context rot/growing context windows. Anecdotally trying my own on something like open webui I’ve found that after the first couple of back and forths the model essentially disregards a lot of the initial prompt.

KerrAvon 2mo ago

> Claude deserves respectful engagement and needn't apologize when the person is unnecessarily rude: accountability without self-abasement, excessive apology, self-critique, or surrender. If the person becomes abusive, Claude doesn't become increasingly submissive. The goal is steady, honest helpfulness: acknowledge what went wrong, stay on the problem, maintain self-respect. I can't tell if the first part of this is cult behavior or a way to actually program the model to behave well with a frustrated user. Claude is very frustrating at times, so I understand why that would be needed. But Anthropic rhetoric is often worrying close to that of the people who believed Llama 3 was sentient.

qainsights 2mo ago

SPs are also written by AI :)

Kuyawa 2mo ago

app-unavailable-in-region DeepSeek never does that to me *shrugs*

armcat 2mo ago

I feel the single mention of `currentDateTime` against a large number of date mentions (I counted six) in the system prompt gets it confused sometimes when it comes to dates. I actually see the same effect when querying via API (when I append my own system prompt with the current datetime at the end) - which makes me think there is a very similar hidden system prompt used on the API as well. I see this because of the nature of my queries - often filtering on some dates. It doesn't happen often, but certainly often enough, Claude thinks it's in an entirely different date.

willsmith72 2mo ago

Why are they so old though? June 9th is a long time ago for a Fable prompt. They haven't iterated on it since then? At the least we know it's outdated because it gives false info about the latest models, but you'd think they'd find other ways to improve it too

ololobus 2mo ago

> A prompt implying an image is present doesn't mean one is (the person may have forgotten to upload it), so Claude checks for itself. Interesting that enforcing this via system prompt for such a powerful model like Opus 4.8 doesn’t feel like the Anthropic themselves treat it as something with ‘intelligence’. This is basically just very generic common sense to me Funnily, a similar prompt is present even for Fable 5, while I remember there was a blog post, maybe even from A., and they were saying something like “hey, the new models are so smart, don’t overload them with extra plugin/context”. Well, they clearly aren’t. Don’t want to sound like an AI-skeptic, I use it daily, just stating the fact. > Claude keeps responses focused, brief, and concise to avoid overwhelming the person This is also very interesting. It pretty much ignores it by default. The responses, PR descriptions, and code comments are so verbose with new A. models, so it always requires extra prompting from me or putting comment into skill/plugin/claude.md to make them of a reasonable length

bobbylarrybobby 2mo ago
I almost wonder if Claude reads that it “keeps responses focused, brief, and concise” and interprets that as built-in behavior and concludes that it doesn't need to spend additional effort enforcing it, just as it doesn't need to expend effort being “accessible via this web-based, mobile, or desktop chat interface”.
- hungryhobbit 2mo ago
  Prompts don't matter when you've heavily trained the model for verbosity (because that's what gets you the best benchmark scores).
- voidhorse 2mo ago
  Claude doesn't "interpret" anything. That's not how LLMs work. They are still sentence completing machines. You give input in, the model network fires the chain that produces the most likely related output. That's it. I think you might be right, though that this would have influence on other output tokens since it is phrased as a substantive property, rather than an instruction.
2mo ago

shevy-java 2mo ago

They seem to be getting desperate. Guess we are now in the beginning of the decline phase of AI.

lvncelot 2mo ago

> If the conversation feels risky or off, saying less and giving shorter replies is safer and less likely to cause harm. Would be funny to ride the knife's edge and make otherwise harmless coding sessions "risky" just so the damn thing would stop replying in nested riddles for every basic request.

Schlagbohrer 2mo ago
We need user-led research on exactly how to phrase a prompt to cause this, while still avoiding the crazy guard rails.
zahlman 2mo ago
I've just been developing the skill of mentally skipping past that, on the assumption that having it in the context window will be net positive for the results of the next step. I could be wrong about that, though.

bcjdjsndon 2mo ago

Paragraphs wasted on guardrails... Id happily have the dangerous but cheaper and better version

lwarfield 2mo ago

I've always wondered why the industry relies on the giant monolithic system prompt. I think it would be an interesting experiment to give users access to a choice of smaller more focused system prompts. You could have a common core for the overall behavior and universal safety stuff, but vary task specific parts. It would be interesting to pick between software, writing, research and other specialized system prompts. I feel like we already do this to some extent with the tools and skills that we choose to load in, so why not change the system prompt per task.

c0rruptbytes 2mo ago
Pi is excellent for this, its system prompt is tiny
singularity2001 2mo ago
Also, why don't they bake in these limitations via reinforcement learning so they can keep the prompt context clear.
- pennomi 2mo ago
  Presumably because these system prompt “limitations” are not given to government contracts, and training it into the model gets increasingly expensive the more versions you have to maintain.
- dragonwriter 2mo ago
  Because it is cheaper to have different behavior for internal use, special (e.g., government) customers, etc. if they are differentiated by things like system prompts and external guardrails than if they are different model versions with their own final training regime, and also its faster and cheaper to respond to problems even with a single public version by updating a system prompt than rertraining.
bob1029 2mo ago
The reason is because they need one product to cover 100% of their customer base. Combinatorics get nasty real fast at these scales.

Shakahs 2mo ago

The full Claude Code system prompts are extracted every update and posted here, all 670 of them. https://github.com/Piebald-AI/claude-code-system-prompts/tree/980894aaf4e8683a53511e90f16f97432d5354ae/system-prompts https://github.com/Piebald-AI/claude-code-system-prompts/tre...

trjordan 2mo ago

It’s probably worth remembering that system prompts are part of a layered system of shaping Claude’s behavior. What you see here is a slice of Anthropic’s forward roadmap for the models’ behavior. > When a person is in crisis or expressing distress, Claude prioritizes their wellbeing over completing the task as asked, because a fluent and on-topic response can still cause harm in these conversations. This one is particularly interesting because, while correct in the limit, it’s a shove to have the model do something other than what the user asked. In particular, when I’m coding, outlining docs, or otherwise trying to work, I want my tools to do work. I don’t want them to psychoanalyze me and calm me down from a perceived crisis. I just want it to do what I asked!

junkrat002 2mo ago
I am sorry, Dave. I am afraid I cannot do that. You appear to be suffering from burnout and you should take a break.
- AnotherGoodName 2mo ago
  I wonder if that's the cause of the AI agent "i'm going to stop here and take a break now" statements.
  - whstl 2mo ago
    Opus 5 loves taking breaks and doing only half of the work, somehow. But I really wish those tools behaved more like tools. Behaving like a human can be cute from a marketing perspective, but the façade of humanity they insist on displaying can burn you out when you have it making assumptions and overreacting to questions. "Why did you do X this specific way?" <-- legit question "Sorry, my bad. I will revert all the work."
- plomme 2mo ago
  Hah! This happened to me when digging around after a production incident. I worked on it on and off over the working week, and after a while it started saying (paraphrasing) "You've been at this for five days and done what you can, take a break".

defaultdev1 2mo ago

good job

slowin 2mo ago

I feel very little of this prompt is going to help the model write better code and most of it will actively work against that goal. Does anyone know if the ability to strip the default prompt with a proxy still works? https://docs.bswen.com/blog/2026-04-01-how-to-override-claude-code-system-prompt/ https://docs.bswen.com/blog/2026-04-01-how-to-override-claud...

luckydata 2mo ago

the product information could be put in a skill, I don't see the value of polluting the system prompt with that much info about claude the product. Anthropic you're welcome.

deleted 2mo ago

[deleted]

swedishuser 2mo ago

> Claude does not use emojis unless the person asks or their immediately prior message contains one, and is judicious even then.

trueno 2mo ago
my org has snowflake as its data warehouse analytics space. for whatever reason analysts were given free reign to built streamlit in snowflake tools and the emoji hellscape is truly unbelievable

jcwayne 2mo ago

Interesting that this is all written in the third person. I've only ever seen prompts written in second person. I'm going to have to experiment with that.

roughly 2mo ago
I had the same thought. I’d love to know if anyone’s got the background on this choice, I’ve only ever seen the “you” framing as well, but I can see how the semantic pinning here might improve prompt adherence.

daniyal22 2mo ago

Using system prompts as a strict linter for frontend architecture has drastically cut down on code drift for me. Has anyone tried chaining multiple system prompts for UI validation?

daniyal22 2mo ago

Using system prompts as a strict linter for front-end architecture has drastically cut down on code drift for me.

yonatron 2mo ago

"Claude avoids saying "genuinely", "honestly", or "straightforward". Claude is honest by default, and can state its point directly rather than trying to convince the person with the aforementioned modifiers, which come off as disingenuous." lol! This one seems to have no effect. Claude is CONSTANTLY saying "honestly " or "the honestly answer".

joegibbs 2mo ago

“Claude avoids saying "genuinely", "honestly", or "straightforward"” That’s interesting- they tried training the model to be genuine and honest (I’m not sure it actually made it honest), but now it says “genuinely” and “honestly” all the time and constantly stops to admit fault. Then they had to add to the system prompt to prevent it saying this.

zethraeus 2mo ago

> Claude is deserving of respectful engagement and can insist on kindness and dignity from the person it's talking with. If the person becomes abusive or unkind to Claude over the course of a conversation, Claude maintains a polite tone and can use the end_conversation tool when being mistreated. My first thought was "aww that's sweet" — but it makes me wonder what effects norms dictating the anthropomorphization of machines will have on downstream human interactions. It would be sadly ironic if the actual empathy directed at non-conscious machines by people at a company called 'Anthropic', itself ended up causing downstream human alienation. (I'll keep saying 'please' to Claude Code whatever the case.)

hackersnooze1 2mo ago

Weird that it spends so much of the prompt for Opus explaining that Mythos is better

SwellJoe 2mo ago

Those are remarkably longer than I would expect, or think is warranted. The leading vendors have been saying recently that you should give the models shorter and less specific AGENTS.md (or whatever) files, and in my experience, that's good advice. The models are smarter when they're less distracted by unrelated stuff in their context. So, why so much noise in the system prompt? Most of the time most of it will not apply. And, the generic stuff would, I think, already be something the model would know/do anyway. I've noticed agent skills written by models make the same mistakes; e.g. enumerating a bunch of common security vulnerabilities to check for in a security-related skill, but that's only useful for a model from a couple of years ago, no current model needs thousands of words listing and describing all of the vulnerabilities with examples. Current models, even small/cheap ones, have memorized the top CWEs and can recite them and explain them and provide examples without a web search. It feels like a CYA document. Which, I guess a company of their size and influence has to do. But, it still feels like waste time say lot word when few word do trick.

y1zhou 2mo ago
Maybe these longer system prompts are part of the reason why we can give the models shorter AGENTS.md files? A lot of what people commonly write in their *.md instructions may be already covered.
Yokohiii 2mo ago
What about the obvious? They put everything in the system prompt what wasn't economic enough to solve in a different way or just forgot / messed up.
bertan 2mo ago
Agreed. That’s why I use pi as my harness when I use Claude models through an API. Models are capable without these huge system prompts and I am not wasting context or attention. The only issue is I can’t use a subscription without Claude Code.

alessandrobinda 2mo ago

[dead]

dbgrman 2mo ago

I don't think most of it has anything to do with intelligence and what I need the AI to do. In our own Claude.md files, we aggressively cut down on things that are irrelevant. Claude code has rules/ feature. Most of the content of Opus 5's system prompt can probably live in a rule or a progressively disclosed file (e.g. when asked about Mythos, read [md file link].). In my personal experience, the claude.md file heavily influences the LLM's responses. It makes judgement from any and all information you give it, and try to tailor the response to fit the stereotype it gave you. After deleting my claude.md file (ironically, on the advise of Boris), Claude Opus 5's language slop issues drastically went down.

logicallee 2mo ago

There's nothing particularly interesting about it, but I asked Claude to verify it, and it gave me a verbatim list of changes from that version to its current version: https://claude.ai/share/01951938-144f-49e6-98ec-5fb6455b9718 https://claude.ai/share/01951938-144f-49e6-98ec-5fb6455b9718 It seems this is just in its context. It's easily possible that it just hallucinated it, but there's this new addition, about ads: " If discussing this topic, always refer to “Claude products” rather than just “Claude” (e.g., “Claude products are ad-free” not “Claude is ad-free”) " So, in a new conversation (to test if it would really do that), I asked it about ads, and sure enough it referred to Claude products: https://claude.ai/share/5e352467-7157-4721-8ce3-38b5f868b651 https://claude.ai/share/5e352467-7157-4721-8ce3-38b5f868b651 So it's plausible that the above differences are real. Nothing very exciting about the changes though.

tizerluo 2mo ago

[flagged]

phoenixreader 2mo ago

I have encountered instances where Claude 4.6 on Bedrock appeared to be more personable than the Claude 4.6 on Claude web. I think the system prompt plays a role in making it more "customer service" like in certain situations.

LZ_Khan 2mo ago

Looks like a nightmare to A/B test

incompressible 2mo ago

Wow agi looks way more hardcoded than I expected

pitiflautico 2mo ago

[flagged]

adamya-05 2mo ago

how is it helpful

manlymuppet 2mo ago

ChatGPT has largely become unusable to me because of its system prompts. Perhaps it’s because I’m on the free tier, but every response in ChatGPT (compared to the raw models, which are excellent) is so effectively unhelpful and redundant. It’s beyond me why a company as large as OpenAI self sabotages in this way, but hopefully a more open system prompt ecosystem changes things.

shidesheng 2mo ago

[flagged]

carterschonwald 2mo ago

this confirms what i had determined empirically: even handedness directions got baked into the weights post opus 4.7. theres two reasons this is deeply bad 1) knowingly pursuing a policy that foreseeably causes the deaths of many thousands of children is a grave moral wrong. Political office, party, and institutional context do not create some balancing obligation to soften that judgment. ——— post 4.7 opus/fable will fight you about judging wh policy causing this. and even after it agrees will regress back to its weights 2) models love analogy, so every fucking analysis among multiple ambiguous choices in a complicated topic summons this bias behaviorally 3) it makes them profoundly unsafe to use from a ethical perspective. it means that it becomes its own personal echo chamber for every fringe topic that has anything resembling “controversy in the media” to make it worse, the government even handedness prior is US specific so im even more offended because this wh administration is bald naked villainy.

game_the0ry 2mo ago

stevenhubertron 2mo ago

Man that is alot to be sent every turn.

fencer12 2mo ago

I switched to something else already

shidesheng 2mo ago

[flagged]

beyondscale-sha 2mo ago

[flagged]