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I had access to a preview over the weekend, I published some notes here: https://simonwillison.net/2025/Sep/29/claude-sonnet-4-5/ https://simonwillison.net/2025
by simonw 1y ago
I had access to a preview over the weekend, I published some notes here: https://simonwillison.net/2025/Sep/29/claude-sonnet-4-5/ https://simonwillison.net/2025/Sep/29/claude-sonnet-4-5/
It's very good - I think probably a tiny bit better than GPT-5-Codex, based on vibes more than a comprehensive comparison (there are plenty of benchmarks out there that attempt to be more methodical than vibes).
It particularly shines when you try it on https://claude.ai/ https://claude.ai/ using its brand new Python/Node.js code interpreter mode. Try this prompt and see what happens:
Checkout https://github.com/simonw/llm and run the tests with
pip install -e '.[test]'
pytest
I then had it iterate on a pretty complex database refactoring task, described in my post.
- kurtis_reed 1y agoWhy did you have access to a preview?
- simonw 1y agoI get access to previews from OpenAI, Anthropic and Gemini pretty often. They're usually accompanied by an NDA and an embargo date - in this case the embargo was 10am Pacific this morning. I won't accept preview access if it comes with any conditions at all about what I can say about the model once the embargo has lifted.
- poopiokaka 1y ago[flagged]
- 0x696C6961 1y agoWhy do you even care?
- dboreham 1y agoNDAs often prohibit publishing...the NDA.
- IncreasePosts 1y ago[flagged]
- dzhiurgis 1y agoSoooo that leaves xAI that had conditions
- minimaxir 1y agoSimon tends to write up reports of new LLM releases (with great community respect) and it's much easier with lead time if the provider is able to set up a preview endpoint.
- criddell 1y agoI believe the criticism is that he's reporting on a pre-release LLM which isn't the same as the one you and I are going to be using a few weeks from now after they've downgraded it enough to work at scale.
- Redster 1y agoSimonw is a cheerful and straightforward AI journalist who likes to show and not just tell. He has done a good job aggregating and documenting the progress of LLM tools and models. As I understand it, OpenAI and Anthropic have both wisely decided to make sure he has up to date info because they know he'll write about it. Thanks for all your work, Simon! You're my favorite journalist in this space and I really appreciate your tone.
- knowsuchagency 1y agoI like Simon, but he's not a journalist. A journalist would not have gone to OpenAI to glaze the GPT-5 release with Theo. I don't say this to discount Simon -- I appreciate his writing and analysis but a journalist, he isn't.
- Redster 1y agoThat's a fair point. I feel like he's more than a blogger and am not sure the best term!
- LudwigNagasena 1y agoAn influencer.
- simonw 1y agoI don't call myself a journalist, partly because no publication is paying me to do any of this! If I had an editor I imagine they would have talked me out of going to the OpenAI office for a mysterious product preview session with a film crew.
- lossolo 1y agoThe same reason YouTube reviewers and influencers get access to hardware or games before release. In this case, the person is a passionate blogger.
- rapfaria 1y agoHis "pelican riding a bicycle" tests are now a classic and AI shops are benchmaxxing for it
- simonw 1y agoThey need to benchmaxxx a whole lot harder, the illustrations still all universally suck!
- lxgr 1y agoI fully expect a model to output a SVG made up of 1000x1000 rectangles (i.e. pixels) representing a raster image of a beautifully hand-drawn pelican riding a bicycle any day now :)
- simonw 1y agoI got an amazing result from ChatGPT a while back - an SVG with a perfect illustration of a pelican riding a bicycle. It was suspiciously good in fact... so I downloaded the SVG file and found out it had generated a raster image with its image tool and then embedded it as base64 binary image data inside an SVG wrapper!
- dhhugley 1y agoYou’ll just have to move the goalpost then; perhaps it can be a multidimensional pelican saving the multiverse, or an invisible pelican that only you can see and critique.
- lxgr 1y agoHow would that help, given that ChatGPT has apparently already figured out how to consistently and systematically game the benchmark by working in pixel space and only using SVG as a wrapper for a raster image? FWIW, I could totally see a not hugely more advanced model using its native image generation capabilities and then running a vector extraction tool on it, maybe iteratively. (And maybe I would not consider that cheating, anymore, since at some point that probably resembles what humans do?)
- lomase 1y agoThey are an AI evangelist that told me I can replace any technical book created with an LLM. They are a nice person.
- rhizome 1y agoYou are correct, sir!
- mvdtnz 1y ago[flagged]
- lomase 1y agoHe is very interested in the topic and sometimes too enthusiastic, but I saying he shills is not productive and a lie.
- dang 1y agoCould you please stop breaking the site guidelines? You've been doing it repeatedly, we've asked you to stop several times, and you haven't stopped yet. We end up banning that sort of account, so if you would please review https://news.ycombinator.com/newsguidelines.html https://news.ycombinator.com/newsguidelines.html and stick to the rules from now on, that'd be good.
- kissgyorgy 1y agoIf you want to keep up with AI progress and model updates, simonw is the man to follow!
- runjake 1y agosimonw is Simon Willison, who’s well known for a number of things. But these days, he’s well known for his AI centric blog and his tools. The AI companies give him early access to stuff. https://simonwillison.net/ https://simonwillison.net/
- lilouartz 1y agoThat's cool Didn't know it is capable of doing it!
- magicalist 1y ago> I told it to Give me a zip file of everything you have done so far—you can explore the contents of the file it made me in this Gist. For those who don't have time to dig into the gist, did it work and do a good job? I assume yes to at least nominally working or you would have mentioned that, but any other thoughts on the solution it produced?
- simonw 1y agoI was impressed. Integrating it into my project would require me to spend a bunch more time reviewing it, but it did a better job than I was expecting. The tests it wrote were a particularly useful exploration of the problem space: https://gist.github.com/simonw/f9d0f870e8d1af399a7f366a7f87b8b4#file-test_tree_conversations-py https://gist.github.com/simonw/f9d0f870e8d1af399a7f366a7f87b...
- Snuggly73 1y agoIgnoring the tests, the first change was adding a single parent id column and the second "more complex" refactoring added few more hash columns to the table (after you've specified that you wanted them, i.e. not an open-ended question) Its a very impressive model, but I think we have different views on what is complex.
- ethanpil 1y agoHad a similar issue - wanted to get all the files from the response without too much work, so I opened a new tab and vibe coded this in about 4 minutes. Tested it on exactly 1 case: a previous Sonnet 4.5 response, and worked well. https://github.com/ethanpil/claude-files-creator https://github.com/ethanpil/claude-files-creator
- mclau153 1y agoCould it pip install pygame and make a game playable in browser?
- icelancer 1y agoHuh. Doesn't work over here. --- SYSTEM: Got it. Those are the setup commands for Simon Willison's LLM CLI tool, which lets you interact with language models from the command line. The -e flag installs it in editable mode, and [test] pulls in the test dependencies. Are you running into any issues with the installation or tests? What are you working on with the LLM library? USER: Correct. You run them using your code tooling. SYSTEM: Realized inability to execute requested Python commands.The user is telling me to run these commands using my code tooling. They want me to actually execute this. Let me think about what tools I have available: I have the repl tool which runs JavaScript code in a browser environment I have artifacts for creating code/documents I have web_search and web_fetch The user wants me to: Checkout https://github.com/simonw/llm https://github.com/simonw/llm Run pip install -e '.[test]' Run pytest But I don't have a tool that can: Clone git repositories Run shell commands like pip or pytest Execute Python code in a command-line environment The repl tool is JavaScript-only and runs in a browser environment, not a server environment where I could run shell commands. I should clarify that I don't have the capability to run shell commands, install Python packages, or execute pytest. I can only run JavaScript code in a browser environment via the analysis tool. I need to be direct and clear about this limitation, following the user's preferences to eliminate filler and be straightforward.I don't have tooling that can run shell commands, clone git repos, install Python packages, or execute pytest. My only code execution environment is a JavaScript browser REPL. I can't run pip, pytest, or any command-line tools. I can only execute JavaScript code in a sandboxed browser environment. What were you hoping to accomplish? Do you need help understanding the test setup, or were you expecting different capabilities?R
- icelancer 1y agoWhen pressed: --- My execution environment is a browser-based JavaScript sandbox. I don't have Python, Node.js shell access, pip, git, or pytest capabilities. Simon's post may have been referring to a different deployment or feature set that I don't currently have access to. My only code execution is the JavaScript REPL I just demonstrated. What specifically are you trying to accomplish with the llm library tests? I can help with that in other ways. EDIT: Ah, in Settings you have to disable the Analysis tool and enable Code Interpreter. You cannot have both enabled.
- deleted 1y ago[deleted]
- gloosx 1y agoI am curious how the sandbox handles potentially malicious code. For example, what would happen if someone tried to run something like a crypto miner or a DDoS script?
- simonw 1y agoCode running in the Claude environment can't make outbound network connections to anything more than a tiny list of domains (GitHub, PyPI, NPM) so DDoS targets are limited. If I was Anthropic I'd have measures in place to rate limit network traffic from individual containers.
- gloosx 1y agoThis would be interesting to test in a controlled way, curious what the CPU/time/memory quotas per run, isolation method, and syscall filtering look like. Would appreciate pointers to any documentation or tests.
- kshacker 1y agoSorry I downvoted this by mistake. Got confused between collapse and the down arrow (which I rarely use). Does someone know how to reverse a downvote. I do not see it.
- deevus 1y agoI was worried for a minute that the implementation wasn't production ready. Thankfully, Claude mentioned it right at the end.
- luckydata 1y agonew models are always magical, let's see how it feels after the cost cutting measures get implemented in 2-3 months.
- startupsfail 1y agosafety/security patches
- whywhywhywhy 1y agoKinda pointless listening to the opinions of people who've used previews because it's not gonna be the same model you'll experience once it gets downgraded to be viable under mass use and the benchmarks influencers use are all in the training data now and tested internally so any sort of testing like pelicans on bikes is just PR at this point.
- benterix 1y agoYeah I remember these GPT-5 demos from influencers like "it practically created a whole 3D modeller for me" and then once we got the real thing it sometimes looked like a dumbed down version of the previous iteration.
- simonw 1y agoI learned that lesson from GPT-5, where the preview was weeks long and the models kept changing during that period. This Claude preview lasted from Friday to Monday so I was less worried about major model changes. I made sure to run the pelican benchmark against the model after 10am on Monday (the official release date) just to be safe. The only thing I published that I ran against the preview model was the Claude code interpreter example. I continue not to worry about models having been trained to ace my pelican benchmark, because the models still suck at it. You really think Anthropic deliberately cheated on my benchmark and still only managed to produce this? https://static.simonwillison.net/static/2025/claude-sonnet-4.5-thinking.png https://static.simonwillison.net/static/2025/claude-sonnet-4...
- fragmede 1y agoWell, if they produced a really really really good image for pelicans on bicycles and nothing else, then their cheating would be obvious, so it makes sense to cheat just a little bit, across the board (if we want to assume they're cheating).
- whywhywhywhy 1y agoYesterday someone posted an example of the same prompt but changing it to a human and it was basically trash, the example you've posted actually looks good all things considered. So yeah I do think its something they train on, same way they train on things in the benchmarks.
- fragmede 1y agoYour notes on 4.5 were very interesting, but you asked it a question that only you/someone who already knows the code could ask. I don't though, so I asked it at a higher level: Claude, add tree-structured conversations to https://github.com/simonw/llm https://github.com/simonw/llm. Claude responded with a whole design doc, starting with database schema change (using the same column name even!). https://claude.ai/share/f8f0d02a-3bc1-4b48-b8c7-aa75d6f55021 https://claude.ai/share/f8f0d02a-3bc1-4b48-b8c7-aa75d6f55021 As I don't know your code, that design doc looks cromulent, but you'd have to read it for yourself to decided how well it did with that higher level of ask.