Claude Fable 5.1 made me a really nice animated pelican

Anthropic released Claude Fable (and Mythos) 5.1, which scores 52.6% on the new Terminal-Bench-Science 0.1 benchmark, up from 24.7% for Fable 5, 29.0% for Opus 5, and 22.4% for GPT-5.6 Sol. In a hands-on test, Simon Willison found that the model's reasoning effort settings (low, medium, high, xhigh, max) produced wildly different results for generating an SVG of a pelican riding a bicycle, with xhigh taking 7 minutes 51 seconds and costing $1.83, while low and medium skipped reasoning entirely.

Today is Claude Fable and Mythos 5.1 day https://www.anthropic.com/claude-fable-and-mythos-5-1 . Anthropic say that Fable 5.1 "sets a new standard for coding, knowledge work, and long-running problem-solving tasks". Their announcement spends a notable amount of time on scientific research, boasting of a 52.6% score on the brand new Terminal-Bench-Science 0.1 https://www.terminal-bench-science.ai benchmark first announced on August 27th https://www.tbench.ai/news/terminal-bench-science-0-1 , up from 24.7% for Fable 5, 29.0% for Opus 5 and 22.4% for GPT-5.6 Sol. Other benchmarks show slightly improved scores, but none as impressive as the Science one. But how well can it pelican? Back in July I wrote about https://simonwillison.net/2026/Jul/16/kimi-k3/ how I was losing faith in the pelican benchmark - its connection to how good the models were at other tasks didn't seem to hold as strongly as it did back in 2025 https://simonwillison.net/2025/Jun/6/six-months-in-llms/ . The most interesting insights I get from it now are comparisons within model families, and particularly comparisons for the same prompt at different reasoning effort levels. Fable 5.1 has five reasoning levels: low, medium, high, xhigh, max - and no option to turn off reasoning entirely. I fixed an issue https://github.com/simonw/llm-anthropic/issues/88 in llm-anthropic https://github.com/simonw/llm-anthropic which caused reasoning traces not to be correctly recorded, then ran some prompts. Here's the full set of pelicans https://tools.simonwillison.net/markdown-svg-renderer?url=https%3A%2F%2Fgist.github.com%2Fsimonw%2F17318f748f8c2b476051ddc2ebeb94a7 for all of the reasoning levels, each with the full reasoning transcript. I'll replicate them here: Next, a bit of a mystery. This is what I got for effort low : The transcript https://tools.simonwillison.net/markdown-svg-renderer?url=https%3A%2F%2Fgist.github.com%2Fsimonw%2F17318f748f8c2b476051ddc2ebeb94a7 options doesn't show any summarized reasoning tokens, and the output token count is 1,998. With Claude that output token count includes reasoning tokens. It took 23.8 seconds and cost 10.017 cents https://www.llm-prices.com/ it=27&ot=1998&sel=claude-fable-5-1 . I bumped that up to medium and got this: Weirdly, that one also shows no reasoning text https://tools.simonwillison.net/markdown-svg-renderer?url=https%3A%2F%2Fgist.github.com%2Fsimonw%2F17318f748f8c2b476051ddc2ebeb94a7 options-1 and used 1,977 output tokens - 21 tokens less than low . It took 23 seconds and cost 9.912 cents https://www.llm-prices.com/ it=27&ot=1977&sel=claude-fable-5-1 . So for this particular prompt "Generate an SVG of a pelican riding a bicycle" Fable 5.1 appeared to skip reasoning entirely at both low and medium settings. Here's high - 29.6 seconds, 2,612 output tokens, 13.087 cents https://www.llm-prices.com/ it=27&ot=2612&sel=claude-fable-5-1 : This one did do a bit of reasoning, summary here https://tools.simonwillison.net/markdown-svg-renderer?url=https%3A%2F%2Fgist.github.com%2Fsimonw%2F17318f748f8c2b476051ddc2ebeb94a7 reasoning : I'm planning the SVG layout for a pelican riding a bicycle, with a sky and ground background, a bicycle with two spoked wheels, frame, seat and handlebars, and a white-bodied pelican with a long neck and orange beak positioned on top. Really not much difference from low and medium , though. At xhigh things got radically different. 36,767 output tokens, 7 minutes 51 seconds, $1.83 https://www.llm-prices.com/ it=27&ot=36767&sel=claude-fable-5-1 The reasoning trace is pretty lengthy https://tools.simonwillison.net/markdown-svg-renderer?url=https%3A%2F%2Fgist.github.com%2Fsimonw%2F17318f748f8c2b476051ddc2ebeb94a7 reasoning-1 , and includes details like this: Adding the eye, wings stretching down to the handlebar grip, orange legs reaching to the pedals, and a small tail feather, while keeping the pelican intentionally oversized compared to the bike for comic effect. ... I'll accept the slight thickness as charming rather than overengineering it. Setting effort to max gave me the best pelican I've seen from any of Anthropic's models. 65,927 output tokens, 13 minutes and 54 seconds, $3.30 https://www.llm-prices.com/ it=27&ot=65927&sel=claude-fable-5-1 : There's a lot to like about this. The background is tasteful, the legs are clearly on either side of the frame, the feet are on the pedals, the wing is on the handlebars, the pelican has a cute blue hat and there's a basket with a fish. It's still not showing nearly the same level of flair as Gemini 3.7 Flash https://simonwillison.net/2026/Aug/13/llm-gemini/ , but I didn't ask for flair - I asked for an SVG, and that's what I got. Some highlights from that reasoning trace https://tools.simonwillison.net/markdown-svg-renderer?url=https%3A%2F%2Fgist.github.com%2Fsimonw%2F17318f748f8c2b476051ddc2ebeb94a7 reasoning-2 : Adding pedal shapes near both feet, with the far foot on the second leg partially visible behind the frame. I'm considering whether to add a small scarf or cap for extra character, but leaning toward keeping it simple to avoid clutter. Now I'm debating a bicycle helmet on the head versus the pelican's signature crest—the beak and pouch already read clearly as "pelican," so a helmet could reinforce the bicycle theme without losing identity, though it might compete with the crest for visual space. I realize the beak at 484,84 would overlap with the dome helmet, so I need to shrink the helmet so it only covers the top of the head, adjusting its arc endpoints to sit higher and narrower so the beak can attach cleanly at the front without collision. ... I'm adding a darker tip region to represent the primary feathers, then reconsidering the trailing edge to include scalloped feather curves instead of one smooth line for a more natural look. ... Now I'm checking the vent line placements on the helmet, making sure they sit far enough inside the helmet's edge given the stroke width and rounded caps, and confirming each vent stays within the helmet's circular boundary. ... I decide skipping a handlebar bell and tire highlights since they're unnecessary additions. Now I'm reconsidering the front fork's curve — the current control point pulls the shape backward when it should bow forward for a proper rake, so I need to shift the control point rightward to fix the fork's lean. On Hacker News, swalsh commented https://news.ycombinator.com/item?id=49525378 49526455 on that Max pelican: Now that it's a solved benchmark, can we get the animated version? I didn't want to spend another $3 so I took the Max pelican and piped it into the default thinking level of High: llm logs -cx | llm -m claude-fable-5.1 -s 'animate this' 6,121 input, 26,201 output = $1.37 https://www.llm-prices.com/ it=6121&ot=26201&sel=claude-fable-5-1 . The result looked like this https://tools.simonwillison.net/markdown-svg-renderer?url=https%3A%2F%2Fgist.github.com%2Fsimonw%2F87282467acb3652e0f99c85155554a32 response , exported here as video since some people have trouble viewing animated SVGs: The wheels in the video are rotating in the wrong direction, but I think that's an artifact of the conversion to MP4 - they seem to be going in the correct direction in the original SVG. Tags: ai https://simonwillison.net/tags/ai , generative-ai https://simonwillison.net/tags/generative-ai , llms https://simonwillison.net/tags/llms , anthropic https://simonwillison.net/tags/anthropic , claude https://simonwillison.net/tags/claude , pelican-riding-a-bicycle https://simonwillison.net/tags/pelican-riding-a-bicycle , llm-reasoning https://simonwillison.net/tags/llm-reasoning , llm-release https://simonwillison.net/tags/llm-release