# Claude Sonnet 5.5
Source: [https://simonwillison.net/2026/Sep/28/claude-sonnet-5-5/](https://simonwillison.net/2026/Sep/28/claude-sonnet-5-5/)
28th September 2026 \- Link Blog
**[Claude Sonnet 5\.5](https://www.anthropic.com/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](https://tools.simonwillison.net/markdown-svg-renderer?url=https%3A%2F%2Fgist.github.com%2Fsimonw%2F1d85a9be7f3ecce26e7f1569161a0d01)\. Sonnet 5\.5 suffered from[the same bug as Opus 5\.5](https://simonwillison.net/2026/Sep/22/opus-and-sol-and-luna/#claude-opus-5-5-max-over-thinks-to-the-point-of-breaking): 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:
Sonnet 5\.5 appears to be almost as good as Opus 5\.5 on some coding tasks, including various[viral 3D animation tricks](https://x.com/claudeai/status/2104674987164782598)\.
The most interesting thing about Sonnet 5\.5 is that it's now the model used for the free tier on[claude\.ai](https://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](https://static.simonwillison.net/static/2026/claude-sonnet-5.5-free-3d-pelican.html), 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\!
Anthropic releases Claude Sonnet 5, a highly agentic AI model with improved reasoning, tool use, and coding capabilities, narrowing the gap with Opus-level models at a lower price. It is available across all plans with introductory pricing.
Claude Sonnet 5.5 is introduced as a faster, lower-cost AI model in the Claude 5.5 family, offering significant improvements in performance, speed, and efficiency for everyday tasks and collaboration.
Anthropic released Claude Sonnet 5, a model with performance near Opus 4.8 at lower prices, but featuring a new tokenizer that increases token counts for English and code by ~30%, effectively raising costs.
Claude Sonnet 5.5 is released by Anthropic, offering major improvements in benchmark scores, cost efficiency, and speed compared to Sonnet 5, with a 70.6% score on Terminal-Bench 4.0.