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Simon Willison's Weblog

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April 2026 newsletter
IA Programmation

April 2026 newsletter

I just sent out the April edition of my sponsors-only monthly newsletter. If you are a sponsor (or if you start a sponsorship now) you can access it here. In this month's newsletter: Opus 4.7 and GPT-5.5, both with price increases Claude Mythos and LLM security research ChatGPT Images 2.0 More model releases Other highlights from my blog What I'm using, April 2026 edition Here's a copy of the March newsletter as a preview of what you'll get. Pay $10/month to stay a month ahead of the free copy!…

Simon Willison's Weblog
TRE Python binding — ReDoS robustness demo
IA Programmation

TRE Python binding — ReDoS robustness demo

Research: TRE Python binding — ReDoS robustness demo If it's good enough for antirez to add to Redis I figured Ville Laurikari's TRE regular expression engine was worth exploring in a little more detail. I had Claude Code build an experimental Python binding (it used ctypes) and try some malicious regular expression attacks against the library. TRE handles those much better than Python's standard library implementation, thanks mainly to the lack of support for backtracking. Tags: security,…

Simon Willison's Weblog
Redis Array Playground
IA Programmation

Redis Array Playground

Tool: Redis Array Playground Salvatore Sanfilippo submitted a PR adding a new data type - arrays - to Redis. The new commands are ARCOUNT, ARDEL, ARDELRANGE, ARGET, ARGETRANGE, ARGREP, ARINFO, ARINSERT, ARLASTITEMS, ARLEN, ARMGET, ARMSET, ARNEXT, AROP, ARRING, ARSCAN, ARSEEK, ARSET. The implementation is currently available in a branch, so I had Claude Code for web build this interactive playground for trying out the new commands in a WASM-compiled build of a subset of Redis running in the…

Simon Willison's Weblog
Quoting Anthropic
IA Programmation

Quoting Anthropic

We used an automatic classifier which judged sycophancy by looking at whether Claude showed a willingness to push back, maintain positions when challenged, give praise proportional to the merit of ideas, and speak frankly regardless of what a person wants to hear. Most of the time in these situations, Claude expressed no sycophancy—only 9% of conversations included sycophantic behavior (Figure 2). But two domains were exceptions: we saw sycophantic behavior in 38% of conversations focused on…

Simon Willison's Weblog
Sightings
IA Programmation

Sightings

/elsewhere/sightings/ I have a new camera (a Canon R6 Mark II) so I'm taking a lot more photos of birds. I share my best wildlife photos on iNaturalist, and based on yesterday's successful prototype I decided to add those to my blog. I built this feature on my phone using Claude Code for web, as an extension of my beats system for syndicating external content. Here's the PR and prompt. As with my other forms of incoming syndicated content sightings show up on the homepage, the date archive…

Simon Willison's Weblog
iNaturalist Sightings
IA Programmation

iNaturalist Sightings

Tool: iNaturalist Sightings I wanted to see my iNaturalist observations - across two separate accounts - grouped by when they occurred. I'm camping this weekend so I built this entirely on my phone using Claude Code for web. I started by building an inaturalist-clumper Python CLI for fetching and "clumping" observations - by default clumps use observations within 2 hours and 5km of each other. Then I setup simonw/inaturalist-clumps as a Git scraping repository to run that tool and record the…

Simon Willison's Weblog
Codex CLI 0.128.0 adds /goal
IA Programmation

Codex CLI 0.128.0 adds /goal

Codex CLI 0.128.0 adds /goal The latest version of OpenAI's Codex CLI coding agent adds their own version of the Ralph loop: you can now set a /goal and Codex will keep on looping until it evaluates that the goal has been completed... or the configured token budget has been exhausted. It looks like the feature is mainly implemented though the goals/continuation.md and goals/budget_limit.md prompts, which are automatically injected at the end of a turn. Via @fcoury Tags: ai, openai,…

Simon Willison's Weblog
Our evaluation of OpenAI's GPT-5.5 cyber capabilities
IA Programmation

Our evaluation of OpenAI's GPT-5.5 cyber capabilities

Our evaluation of OpenAI's GPT-5.5 cyber capabilities The UK's AI Security Institute previously evaluated Claude Mythos: now they've evaluated GPT-5.5 for finding security vulnerability and found it to be comparable to Mythos, but unlike Mythos it's generally available right now. Tags: ai, openai, generative-ai, llms, anthropic, claude, ai-security-research, gpt

Simon Willison's Weblog
Quoting Andrew Kelley
IA Programmation

Quoting Andrew Kelley

It's a common misconception that we can't tell who is using LLM and who is not. I'm sure we didn't catch 100% of LLM-assisted PRs over the past few months, but the kind of mistakes humans make are fundamentally different than LLM hallucinations, making them easy to spot. Furthermore, people who come from the world of agentic coding have a certain digital smell that is not obvious to them but is obvious to those who abstain. It's like when a smoker walks into the room, everybody who doesn't…

Simon Willison's Weblog
We need RSS for sharing abundant vibe-coded apps
IA Programmation

We need RSS for sharing abundant vibe-coded apps

We need RSS for sharing abundant vibe-coded apps Matt Webb: I would love an RSS web feed for all those various tools and apps pages, each item with an “Install” button. (But install to where?) The lesson here is that when vibe-coding accelerates app development, apps become more personal, more situated, and more frequent. Shipping a tool or a micro-app is less like launching a website and more like posting on a blog. This inspired me to have Claude add an Atom feed (and icon) to my…

Simon Willison's Weblog
The Zig project's rationale for their firm anti-AI contribution policy
IA Programmation

The Zig project's rationale for their firm anti-AI contribution policy

Zig has one of the most stringent anti-LLM policies of any major open source project: No LLMs for issues. No LLMs for pull requests. No LLMs for comments on the bug tracker, including translation. English is encouraged, but not required. You are welcome to post in your native language and rely on others to have their own translation tools of choice to interpret your words. The most prominent project written in Zig may be the Bun JavaScript runtime, which was acquired by Anthropic in December…

Simon Willison's Weblog
LLM 0.32a0 is a major backwards-compatible refactor
IA Programmation

LLM 0.32a0 is a major backwards-compatible refactor

I just released LLM 0.32a0, an alpha release of my LLM Python library and CLI tool for accessing LLMs, with some consequential changes that I've been working towards for quite a while. Previous versions of LLM modeled the world in terms of prompts and responses. Send the model a text prompt, get back a text response. import llm model = llm.get_model("gpt-5.5") response = model.prompt("Capital of France?") print(response.text()) This made sense when I started working on the library back in April…

Simon Willison's Weblog