8 ms·
Benchmarking Opus 5 on SlopCodeBench
- tamimio 2mo agoSo many benchmarks more the models themselves.. just make one unified standard to benchmark all or stop calling it “benchmarking” as this word lost its meaning.
- dcl 2mo agofinally the benchmark for me
- dhorthy 2mo agoi hope that is because you hate slop and not because you write it
- Johnny_Bonk 2mo agoI haven't joined your chats in a while but glad to see you put this together, I truly feel as though opus 5 is not much of an improvement. The only time i ever felt a wow factor was opus 4, 4.6 and fable pre trump admin lobotimizing
- dhorthy 2mo agoyeah this was just a start - the fastest cheapest thing we could try for a brand new model. I'm hoping to do some more work with sol/fable in the mix as well as exploring more languages and curating the problem set to include more of the benchmark I also kinda felt like opus4.5 was dumber than 4.1 personally, maybe a little biased since 4.5 was 2.5x faster and 2.5x cheaper seems to indicate its a smaller model
- Johnny_Bonk 2mo agoyeah i agree
- dan_gee 2mo ago[flagged]
- scrollaway 2mo agoHow is this useful or insightful? You ever go to forums full of entomology specialists and tell them you don’t understand their fancy terms?
- dan_gee 2mo agoMy point is that the differences between these models are so minor that obsessively benchmarking them comes across as navel-gazing.
- Johnny_Bonk 2mo agolike all good science, measure everything
- joatmon-snoo 2mo agoThe evidence that proves a model is actually a step function change is these benchmarks. If a model isn’t a step function change? Welcome to research.
- deleted 2mo ago[deleted]
- killingtime74 2mo agoDid you not benchmark latest GPT 5.6 or GLM 5.1/Kimi K3 because of cost? I can run them if you share how you ran them
- dhorthy 2mo agono i'm spinning those up at some point this week. here's the first few prompts I used (claude opus 5 as the research orchestrator), (these were interspersed with lots of tools and assistant messages but it should get you kicked off. > fetch this article for slopcodebench and help me run an eval on a subset of problems with opus 5 https://arxiv.org/html/2603.24755v1 https://arxiv.org/html/2603.24755v1 > Get all the context, fetch any mentioned repos, and then propose a plan to me. > i have an anthropic API key in .... > Let's do the three challenges with Opus 4.8 and Opus 5 and Fable please. I like your minimal set. Let's try it. What do you need from me? > Actually I changed my mind. I want to do two of the easy ones you picked and then I want you to pick the one with more checkpoints, maybe one of the harder ones, not the very hardest one but one with a higher number of checkpoints. > Actually let's do one easy, one medium, and one hard problem please. If we have a hard problem I'd like to see that. > lets rock - i think lets just do opus 4.8 and sonnet 5 and opus 5 since we our ZDR will block fable
- killingtime74 2mo agoThank you!
- cute_boi 2mo agoOpus 5 is an overconfident stupid model. It tries to generate too much slop, tries to act like everything will fall. I have reversed back to fable and codex sol.
- dhorthy 2mo agoyes sol is still my daily driver for most coding tasks I did find opus 5 quite handy for general knowledge work and visual design, without the cost of fable (e.g. the graphics in this post are made by opus 5) but its not noticeably better than opus 4.8 in those regards, and I would not miss it if forced to go back to 4.8
- roncesvalles 2mo agoI almost prefer Opus 4.8. Opus 5.0 has the overly scholastic tone of Fable but without the intelligence.
- patwolf 2mo agoWe've been running automated code reviews on claude with a bunch of skills/subagents with different specialties. Any review feedback is then fed back into claude to fix. Since switching to Opus 5 I've noticed the reviews are overly pedantic, and that leads to feedback loops where each fix generates more feedback, which requires more fixes, i.e. slop. I had, for example, a simple SQL migration script with a single CREATE TABLE. After a few rounds of review, it ballooned into a complicated 200 line script. I'm not ready to blame Opus 5 for being stupid. Perhaps we have a prompt buried somewhere that's essentially asking it to be pedantic, and it's just obeying the prompt.
- latentsea 2mo ago> I'm not ready to blame Opus 5 for being stupid. Perhaps we have a prompt buried somewhere that's essentially asking it to be pedantic, and it's just obeying the prompt. This is a known failure mode. Sadly, working on a software engineering team doing agentic engineering now means we need to build and maintain suites of evals that measure these things, so that we can measure the effects of changes to harness components including how they perform under model upgrades. But... for a traditional software engineering team that has no experience in this... How do we even do it?
- knighthacker 2mo agoThis is where Opus 5 shines
- Vgoose 2mo agoNice! I actually ran across this paper+benchmark recently, too. It's the first I've found that start to aim at some of the non-functional and longitudinal requirements that I think have always been an important part of writing production code. It's especially relevant now that models are good enough to solve ~most point-in-time problems. Some relevant but disconnected thoughts: - deterministic scores are so nice - what "maintainable" is is probably some high dimensional space described by these signals; it'd probably require some human labeling to figure out where this space is - another signal I've been thinking about and I'm seeing increasingly get brought up is the state space of a system; I'm seeing formal methods pop up a lot recently
- dhorthy 2mo ago> - what "maintainable" is is probably some high dimensional space described by these signals; it'd probably require some human labeling to figure out where this space is this is a nicely succinct way to put this - a multi-dimensional space where no single metric is really useful state space of the system is interesting too. I would guess that for any production software with dependencies like databases/third parties that might be too hard to measure, but if you can silo off parts of your system into bounded state machines, it may be a value metric on some module behind a clean interface. I think the kubernetes control loop model is a great instance of this, a handful of scoped components that own a control loop across a well-defined state machine, that can operate / recover in the face of most network partitions or downtime - the promise of CRDTs but rather more a pragmatic approach to it
- NitpickLawyer 2mo ago> another signal I've been thinking about and I'm seeing increasingly get brought up is the state space of a system State space of a system AND the way to make it accessible / visible to a model. Many times a model can work magic if it can "see" the state of a system in a way that suits it. That's why sometimes having a cli added to the environment seems like such a big unlock. Because that cli usually takes a complex state and allows visibility into it, and possible manipulation in a structured way.
- 2mo ago
- sothatsit 2mo agoThis matches my experience of Opus 5 being a nice improvement over Opus 4.8, but not being revolutionary like Fable felt. I’ve now replaced my use of Opus 4.8 xhigh with Opus 5 medium, and I’m using less tokens and it’s quicker. I can understand people being annoyed by its writing style but for getting work done that really doesn’t bother me. I’ve been really enjoying using it.
- fastball 2mo agoMedium vs High? Why? From all the charts I've seen the performance jump is pretty large from med -> high (not as noticeable from high -> xhigh).
- sothatsit 2mo agoIf I need something smarter I use Fable. Medium works well and is quick. Opus 5 medium feels much better to me than Opus 4.8 medium.
- dhorthy 2mo agoyeah someone will have to re-run this bench on various effort levels. unfortunately it is not cheap
- conception 2mo agohttps://cognition.com/frontiercode https://cognition.com/frontiercode Quality vs cost - medium is the sweet (perhaps better too!) spot.
- ajwin 2mo agoTo what degree is this a harness/system prompt problem? Models maybe should implement new stuff with as little impact on the existing stuff as possible by default? A simple system prompt for it to always check the code after task completion for proper simplifications, abstractions and cleanups before returning to the user? Instructions to retain "story like" readability of the code.
- dhorthy 2mo agoI agree this is an option, and the next thing on my radar is to try with a more realistic "factory-shaped" harness where you have feedback from linters and other models after each coding episode that refines the architecture. For readability specifically, I've found it hard to get the models to do this with prompting. If you've talked to opus/fable for a long time on prose writing you probably felt this too
- igregoryca 2mo agoAt least for Claude Code, putting "run /simplify at the end" in an "implement the plan" skill helps a little. It still often leaves new code in bizarre places, and/or with bad/alien-sounding names and comments.
- dhorthy 2mo agoYeah I would hold that models don’t know how to simplify because most rl/benchmarks doesn’t penalize complexity
- deleted 2mo ago[deleted]
- lostdog 2mo agoClearly the first step of slopbench2 should be to have the agent first write its own harness!
- renezander030 2mo ago[flagged]
- akurilin 2mo agoReally hoping that all of the attention you're bringing to the longitudinal sloppification of codebases makes it back to the labs and creates some pressure to improve that trait of the models. This new benchmark seems promising. At the same time, I imagine it will be hard for them to prioritize this over improving flashy one-shots of impressive zero-to-one feats that demo so well and attract more customers. Can we have simonw make "pelican on a bicycle after 1000 requests for iteration" popular?
- dhorthy 2mo agoi laughed at the pelican bit its good yes the labs will always prioritize the vibeslop dopamine casino as far as I can tell - making the models useful and addictive for unsophisticated users, sometimes at the expense or at the very least at the ignorance of the needs of power users
- zparky 2mo agoI remember reading a blog post a year or two ago about prompting like a printer driver and asking for increasingly ridiculous changes like time travel or wormhole capability. I don't know if I hallucinated that post but I haven't been able to find it again and I REALLY wish I could
- delbertty 2mo agoMostly a harness problem in my experience. Slop accumulates when the agent can touch anything, so constraining it to one seam and having it add alongside rather than edit in place does more than model choice.
- cesarvarela 2mo agoPlease add Fable; a good benchmark should show that Fable is less prone to just autocomplete and instead pushes back or is at least more tasteful.
- dhorthy 2mo agoYeah the main reason I skipped fable was because we have a ZDR with anthropic and I didn’t feel like spinning up another account to circumvent that. Next run will have fable and sol
- sqemo 2mo ago[flagged]
- 4by4by4 2mo agoI'd be curious to see the raw test results. I have a suspicion that most models will miss the `database_migration` Checkpoint 2 test that includes a `default_value` because it could be interpreted as either a JSON-literal or a SQL-expression. There might be other tests as well that are prone to failure for reasons other than the reasons cited in the paper. I think a cool experiment would be to adjust the order of the features implemented (e.g. checkpoint 3 then 2 then 5 then 4) where dependencies allow it. Then one could account for some checkpoints being more difficult than others.
- dhorthy 2mo agooh i really like the idea of flipping around the order of checkpoints and comparing results. Could be an interesting way to increase/decrease difficulty even i will look into how easy it would be to zip up some subset of the results without leaking anything...probably doable
- subarctic 2mo agoI still don't have access to Opus 5. I'm on the latest version from Homebrew, I guess the update hasn't made it there yet
- sethherr 2mo agoWhy are you on the version from homebrew?
- sunaookami 2mo agoHave you tried running /model claude-opus-5?
- piazz 2mo agoGreat writeup. The excessive function thing has always driven me crazy; I guard against this explicitly in Claude.md. I have found that models are generally poor at managing refactors / complexity while also implementing new features. But I’ve had some success with a semi-lights-off approach where you decompose it and prompt the model adversarially in a second pass to look for new rough edges and areas of complexity or refactors that might simplify the codebase. So I’d be very curious to see this benchmark but with something like a periodic “refactor turn” interleaved in. Also eager to see Fable benchmarked; anecdotally that was the only model whose code I felt I could actually trust to not review closely.
- joka88xj 2mo ago[flagged]
- willsmith72 2mo ago> The big headline is that Opus 5 got a 24% on the small subset of the benchmark that I ran - not much higher than Opus 4.6's 17% strict pass rate in the original paper. a 41% improvement is not much higher? come on that's just doomer
- well_ackshually 2mo agoIf you tell me that 76% of your code is dogshit but that's it's a massive improvement over your previous 83%, I'm firing you.
- 1123581321 2mo agoI’d enjoy working with such a person, a bleak Eeyore-Gilfoyle.
- willsmith72 2mo agoyou're the manager who started with 83% dogshit. i'm escalating or moving teams.
- weiliddat 2mo agoFor most of these benchmarks, I feel like a p50 and p95 (using SWE salary as a proxy?) human benchmark as reference would be interesting. Edit: FWIW the paper the post quoted has repositories as slop baseline https://arxiv.org/html/2603.24755v1#S4.SS2 https://arxiv.org/html/2603.24755v1#S4.SS2
- robbomacrae 2mo agoSCB is definitely an underrated benchmark. For me the unique selling point is that it more closely mirrors software development by not stopping after a single task. The agent has to keep code clean. The only disadvantage is all the problems are greenfield and not git inited so the agents don’t make use of git diffs. I’ve used SCB as part of my assessment of agent skills (superpowers, GSD etc) https://orcabot.com/labs/do-skills-improve-coding-agent-accuracy https://orcabot.com/labs/do-skills-improve-coding-agent-accu... There is a small but growing community on discord for discussing SCB so if interested please join https://discord.gg/BrC4BA9sVj https://discord.gg/BrC4BA9sVj
- dhorthy 2mo agoso wait is the finding that most of those skills reduce pass rates against SCB? wild
- robbomacrae 2mo agoYep that was interesting but imho not completely unexpected. My original hypothesis was that these agent skills are castles built on sand and that the models would quickly adapt and make them redundant. Also the skills use up context and I think a lot of them partially focus on investigating a large complex codebase properly... which is wasted on greenfield projects.
- gck1 2mo agoI did a full circle and essentially dropped all of my personal static workflows encoded in skills because I observed recent models picking better ad-hoc workflows for particular problems, when a static one would force a subpar one. It seems like we all tried to contain and organize a system that simply prefers to select its own organization. Which makes me to think that these skill packs of workflows are really made to make it easier for humans rather than agents.
- robbomacrae 2mo agoThats right and to go even further I'm judging them on a metric they didn't necessarily target. A client I work with uses skills such as these to apply their own processes on the agentic development lifecycle. But users should also understand the trade-offs. I think it's intuitive that the extra steps and processing invoked by these skills adds to the token cost - this benchmark aims to put numbers on that as well as time and accuracy.
- mellosouls 2mo agoThis is nice, but would be really useful measured against human performance, and yes - I understand that is likely a difficult challenge. Many people though are going to read the headline figures and think it means - say - Opus 5 is only a quarter the strength of a human coder.
- WilcoKruijer 2mo agoI hope the big labs will start using this benchmark in their RL pipelines. Reducing complexity in generated code should be the number 1 priority, in my opinion. The holy grail for me is models implementing features while reducing LoC (i.e., choosing the right abstractions). What is also nice about this benchmark is that it can be used to iterate on prompts/skills for reducing code complexity.
- stbenjam 2mo ago> I hope the big labs will start using this benchmark in their RL pipelines. Labs do not train on benchmark data (allegedly). They can train on similar problems, but benchmarks have specific strings in them that labs are supposed to be aggressive in filtering out of their training corpora.
- falsemyrmidon 2mo agoIt's just as easy to go too far in the direction of shoving too much logic on a single line in the name of reducing lines of code.
- Normal_gaussian 2mo agoIt should be hoped that whoever is doing this is using automatic formatters; though of course metrics relating to code complexity are best done as measures over the AST.
- jerf 2mo agoI would at least consider the possibility that they already are, and this is how it is going. It could be a fundamental architecture problem for LLMs. It's not like "slop" is a new problem and I'm sure they'd love to announce a new model that generates much less "slop". The fact they've never so much as mentioned it suggests to me that it's not something they've been able to fix.
- tracker1 2mo agoI call out specifically in my agent/claude file that I want and prefer simpler solutions over complex enterprise pattern usage and overuse of abstractions. It tends to help a bit, but often I have to give feedback in my review step. My typical workflow when AI assisted is what I call human gatekeeping... I'll plan out next steps with the agent, updating a TODO.md file with what needs to be done, then a fresh context to implement the next step(s), and review the code before committing to git. I may iterate/stash or even reset a few times before it's "good enough"... it is rarely close to what I would do myself, but often as good as what I've gotten from other developers IRL on projects. This includes updating the documentation area(s) of a project as well as testing. I also tend to lean on ./run/* for scripts that will run/test various portions of the project... getting the agent to use these is sometimes harder than it should be, as I want it to specifically exercise a lot of things through the process... there are also times where it will try to change a valid test that's failing instead of fixing the code. That's the most irritating part. Some models are annoying, some feel like pure magic at times.
- drcongo 2mo ago> [...] with Opus 5 writing five times the number of functions/callables than Opus 4.8 over the course of the same set of challenges. Is this bad? I have McCabe complexity switched on in Ruff and find it a handy watermark for when something should be broken up into smaller, individually testable callables. Five times as many callables could make for much more readable and testable code.
- dandaka 2mo agoCan we use those metrics in a review pass for every PR? So review agent will have to pinpoint new complexity and propose refactoring or justify increase?
- vintermann 2mo agoThis benchmark makes me worry a bit that people will just ask their model to reimplement everything from scratch once their requirements become more clear.
- dhorthy 2mo agowhy would that worry you?
- vintermann 2mo agoWasting a lot of power.
- swiftcoder 2mo agoI wonder to what extent we could steer performance on this benchmark, by providing an adversary model that penalises code duplication and overall lines of code?
- anentropic 2mo agoSo far my 'solution' to this has been periodically run a separate round of whole-codebase code review (preferably Fable) and then rounds of refactoring off the results of that
- thatfunkymunki 2mo agoyes, this has been my preferred approach as well. Too much risk of very deep local maxima otherwise.
- mengram-ai 2mo ago[flagged]
- dmrivers 2mo agoI always have Claude recite a pledge before starting coding to fix redundant code it notices over time. It does seem to find redundancies, but only when I point out bugs, that's when it goes into fixing mode and actually applies my Don't Repeat Yourself preference from the CLAUDE.md. The original paper cited by this post does try to see if improved prompting will make a big difference in the end using a `plan_first` prompt variant, but find no influence on pass rate at the end of the benchmark. The `plan_first` seems to assume coding agents will just refactor once they finish features, but I don't think they tend to refactor significantly unless they are told to fix bugs rather than build features. The benchmark leaves tests hidden with no fail-to-pass feedback, so that may be why degradation is monotonic.
- try-working 2mo agoThis is just superstition.
- notnaut 2mo ago“Coding” can be more like communing with an otherworldly presence via esoteric gesturing nowadays than ever. Superstition leads countries and companies.
- KyleTheDev 2mo agoEvery day we get closer to being mystics having to commune with orbs in order to create phenomena.
- organsnyder 2mo agoMusk definitely gives Dukat vibes.
- 2close4comfort 2mo agoyeah like the palantíri in Lord of the...oh god its too late.
- 2mo ago
- insumanth 2mo agoOpus models were straightforward to review. But Opus 5 is very different.
- adamtaylor_13 2mo agoI may be crucified for asking this but: is there any proof that slop matters beyond our sensibilities as developers? If the code is ugly, but defects are low—does it matter? If the code is hard to read, but clients are happy—should I care? Genuinely asking. Weird times we live in.
- jdm2212 2mo agoIt's the eternal question with any kind of tech debt -- is it worth a little more velocity now in return for medium-to-long term slowdown? And there's no general right answer.
- dhorthy 2mo agoagree, i think the implication is that low quality code is harder to change in the future
- bodeadly 2mo agoLike anything in coding, it depends. LLMs are good at following conventions. If what you're doing has been done a 1000 times before and there is a good bias, it will produce good results. This is why LLMs are so good at the leafy parts and even the branches the leaves are connected to. But there's always something unconventional about a codebase. If there weren't, it wouldn't be worth writing.
- Majromax 2mo ago> I may be crucified for asking this but: is there any proof that slop matters beyond our sensibilities as developers? That's precisely what this benchmark tries to quantify. Since the benchmark incrementally expands the scope of each problem, 'sloppy' code is code that is hard to later modify. I know this firsthand: the dumbest coder I've ever worked with was 'myself six months ago'. That jackass never keeps the documentation up to date and hard-codes things that ought to be exposed as configuration. The SlopCodeBench is an important but early-stage probe in this direction.
- paffdragon 2mo ago> is there any proof that slop matters beyond our sensibilities as developers? I've seen a few papers recently on the topic in terms of LLM, here is two I found by quick googling * "Does Code Cleanliness Affect Coding Agents? A Controlled Minimal-Pair Study" https://arxiv.org/abs/2605.20049 https://arxiv.org/abs/2605.20049 "Our findings suggest that traditional maintainability principles remain highly relevant in the era of AI-driven development, shaping the computational cost and navigational efficiency of coding agents." * "Code for Machines, Not Just Humans: Quantifying AI-Friendliness with Code Health Metrics" https://arxiv.org/abs/2601.02200 https://arxiv.org/abs/2601.02200 "Our findings confirm that human-friendly code is also more compatible with AI tooling." "Investing in maintainability not only helps humans; it also prepares for large-scale AI adoption." > If the code is ugly, but defects are low—does it matter? > If the code is hard to read, but clients are happy—should I care? For you who wrote it and are the sole developer, maybe not. But if you want to have other contributors or hand it off, then it can be a problem. New devs joining the project may not want to work with it and will push for a rewrite that will cost money or need to spend extra time on working with code that is hard to work with for them which will cost money. And from the papers above it seems this also affects LLMs as well as they seem to work more efficiently with "cleaner" code.
- spicyusername 2mo agoIt'd be interesting to compare this to human teams, given the same challenges.
- javed6542 2mo agoGood benchmark. Although, why did they have to give it such a unprofessional name?
- jrflo 2mo agoThe author of the original paper did not include error bars on the cost and quality results, which is a bit alarming. They did include a +/-, but did not list explicitly if that means standard deviation, range, or 95% CI, etc. Another table is listed as that being one standard deviation. If we take those results to be a standard deviation as well, I think we can conclude that there is no statistical difference between the outcomes of all models in terms of quality and cost, as the error bars are all overlapping.
- nikhilsimha 2mo agothe last note about the agent sending emails without approvals is a very common problem!
- Sattyamjjain 2mo ago[flagged]
- antrichards 2mo ago[dead]