Simon Willison
Aug 9
Quoting Claude Opus 5 system prompt
Claude Fable 5 and Claude Mythos 5 were first released on June 9, 2026. On June 12, 2026, Anthropic suspended access to both models to comply with U.
llm-anthropic 0.28
The release of llm-anthropic 0.28 introduces support for Claude Fable 5.1, enabling default display of reasoning traces for compatible models. It also adds a new llm_anthropic.ClaudeRefusal exception to handle cases where Claude returns a refusal. These updates enhance debugging and error handling for users of the library.
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Simon Willison
Oct 6
llm-mistral 0.16
The release of llm-mistral 0.16 introduces support for reasoning models, notably the newly released Mistral Large 4. This update expands the library’s capabilities to handle more advanced language model tasks that involve reasoning. The release is tagged under llm, mistral, and llm-reasoning.
Simon Willison
Sep 1
Claude Fable 5.1 made me a really nice animated pelican
The article discusses Anthropic’s Claude Fable 5.1 release, highlighting its claimed improvements in coding, knowledge work, and problem‑solving, particularly a 52.6% score on the new Terminal‑Bench‑Science 0.1 benchmark. The author examines the model’s performance on the pelican benchmark, noting that Fable 5.1’s five reasoning levels (low, medium, high, xhigh, max) sometimes skip reasoning entirely for certain prompts, as evidenced by token counts and cost metrics. The piece provides detailed transcript data for each reasoning level when generating an SVG of a pelican riding a bicycle.
Simon Willison
Sep 22
llm-anthropic 0.29
The article announces the release of llm‑anthropic version 0.29. It introduces support for the Claude Opus 5.5 model, allowing users to invoke it with the command line syntax `llm -m claude-opus-5.5 "prompt goes here"`. The release is tagged under llm and anthropic.
Simon Willison
Sep 18
Quoting Thariq Shihipar
The article announces that Claude Code will now support AGENTS.md files starting with version 2.1.277. If a CLAUDE.md file is absent in a folder, Claude will automatically look for and use AGENTS.md, leveraging Claude Code mods to customize the harness. The built‑in mod is available for use, and users can also create their own custom project instructions.
Simon Willison
Aug 24
llm-anthropic 0.27
The release of llm‑anthropic 0.27 updates the Anthropic plugin for LLM to be compatible with the newly released anthropic v1.0.0 Python library, which has switched from httpx to httpx2. This mirrors a similar change made by OpenAI in their v3.0.0 release two weeks prior. The update includes a migration guide and a pull request that ensures tests pass after upgrading to anthropic>=1.
Simon Willison
Aug 23
Quoting Drew Breunig
The article reflects on the shift in perspective after the release of Fable, a new model that promised to solve many coding challenges at a comparable or lower cost. Prior to Fable, developers felt it was pointless to invest heavily in coding tools or context strategies, as newer models would likely render them obsolete. However, Fable’s performance was so impressive that, despite its high cost, it prompted a reevaluation of how work was distributed across different models such as Opus, 5.6, K3, and GLM.
Simon Willison
Oct 22
Donating Agent Skills to the Agentic AI Foundation
Anthropic has announced that it will donate the Agent Skills standard to the Agentic AI Foundation (AAIF), a Linux Foundation‑backed organization co‑founded with Block and OpenAI. The move follows Anthropic’s earlier declaration that skills would be an open standard and aligns with the AAIF’s recent role as the home of the Model Context Protocol (MCP). The donation is part of Anthropic’s commitment to keeping Agent Skills community‑driven and vendor‑neutral.
Simon Willison
Oct 16
Quoting Addy Osmani, Morgan Westlee Lunt, and Qing Wang
The article discusses a shift in code review practices, moving from a final gate to continuous review that functions like spellcheck during coding. It highlights how the Claude Code team uses the Claude AI to catch routine mistakes before human reviewers intervene, allowing developers to focus on higher-level issues. The piece references insights from Addy Osmani, Morgan Westlee Lunt, and Qing Wang on this evolving approach.
Towards Data Science
Jul 16
How to Get the Most Out of Claude Fable 5
Maximize your Claude Fable 5 usage The post How to Get the Most Out of Claude Fable 5 appeared first on Towards Data Science .
Simon Willison
Sep 16
Claude Cowork and chat are now one Claude
Claude Cowork and the standard chat interface are merging into a single Claude experience, allowing users to hand over tasks or ask quick questions that the system will continue to handle even after the laptop is closed. The rollout will begin with Pro and Max plan users across web, desktop, and mobile, and will extend to new users on these plans over the coming weeks. This integration suggests Claude is evolving into a general agent, simplifying the distinction between Cowork and regular Claude usage.
Simon Willison
Sep 11
Quoting Boris Cherny
The article discusses how production code generated by Claude, Anthropic’s AI, should meet higher standards than human-written code. Anthropic enforces this through numerous guardrails such as lint rules, extensive testing, Claude-driven end‑to‑end tests, daily fuzzers, automated code and security reviews, and automated refactoring. These measures aim to prevent the code from becoming difficult to maintain.