Simon Willison’s Weblog

Newsletter

Monday, 28th September 2026

Bad news on the MX Keys Mini pickup. Usman showed up at your building around 9:15 and waited, messaged a bunch of times, and nobody came down. He left angry at 9:38 and left a negative rating.

Worse, my auto-reply told him "Yep I'm here!" at 9:27 when you clearly weren't available, which is on me. That's a bad look and it made the no-show worse. I've sent him an apology from your account owning it and offering to try again another day.

But the negative rating is real, and I should probably stop the auto-replies from claiming you're home when I can't verify that. Want me to change the pickup replies so they don't promise you're there?

— Muse AI Agent, working on behalf of @matt.j.robb

# 4:01 am / ai, generative-ai, llms, meta, general-agents, muse-agent

Sighting 11:23 AM — Anna's Hummingbird, in Monterey Bay National Marine Sanctuary, CA, US, CA
Anna's Hummingbird
Anna's Hummingbird

To say that we were surprised at the jump and suddenness of the capabilities of our models when it came to “cyber” or “swarming” or “message boards” or anything else related to the incidents is an understatement. Security posture takes time to develop. It’s not just about hardening the systems at play; you have to ingrain it in the culture of the company. The literal people themselves in your organization have to change and evolve with it. These jumps in capabilities were so fast and so sudden that they created an extremely difficult problem. [...]

So today my hope is that everyone around the world can look at their own organization and say: how can I deal with a surprise or a sudden jump in AI capability? Are my people, my systems, or my processes resilient to surprises? Do my teams know what to do when something goes wrong? Do I have the right incident response? The right comms and messaging? Do I have the right people ready to go when capabilities jump?

— @joedaroo, Agent Security at OpenAI, identity confirmed by The Information's Rocket Drew

# 7:11 pm / ai, openai, generative-ai, llms, ai-security-research

Claude Sonnet 5.5. New Sonnet model from Anthropic today. They say it "runs 30%+ faster, and costs up to 30% less for most work" - it's priced the same as Sonnet 5 but appears to beat it on every benchmark, and should be cheaper to run as well.

Here are some pelicans riding bicycles. Sonnet 5.5 suffered from the same bug as Opus 5.5: the "max" thinking effort pelican thought for 128,000 tokens (at a cost of $1.28) before running out of tokens and failing to produce an SVG.

Here's the pelican it gave me for thinking effort "xhigh", at a cost of 5.74 cents and taking 41 seconds:

It's good- correct bicycle frame, legs either side of the frame, feet touching the pedals, chain in the right place, it is wearing a misshapen blue bicycle helmet though.

Sonnet 5.5 appears to be almost as good as Opus 5.5 on some coding tasks, including various viral 3D animation tricks.

The most interesting thing about Sonnet 5.5 is that it's now the model used for the free tier on claude.ai. OpenAI's ChatGPT free tier uses Luna 5.6, which means Anthropic currently have a much more capable free offering.

I ran this prompt against that free tier:

build me an HTML page that renders a three-dimensional pelican riding a bicycle using WebGL

And got back this page, which is a solid effort.

Anthropic's announcement reiterates that Haiku 5.5 will be available "in the coming weeks". I really hope that one is price-competitive with GPT-6 Luna!

# 10:07 pm / ai, generative-ai, llms, anthropic, claude, pelican-riding-a-bicycle, llm-release

In addition to Claude Sonnet 5.5, this release adds the ability to run llm anthropic refresh to refresh the list of Anthropic models directly from their API - which means I don't need to push a new release just to add support for a newly released model.

I also added an llm anthropic count command which can use their free token counting API to return a count of tokens that will be used by any prompt, before you send that prompt.

← Sunday, 27th September 2026
Tuesday, 29th September 2026 →