Claude Fable 5.1 is Anthropic’s advanced model focused on agentic coding, long-running workflows, and knowledge-intensive tasks. It improves over Claude Fable 5 particularly in large code refactoring, frontend and visual code generation, finance, and analytical workloads. It is also designed to produce more concise plans and summaries. With a 1-million-token context window and support for up to 128K output tokens, Claude Fable 5.1 can handle large codebases, lengthy documents, and extended multi-step workflows. It accepts text, images, and files such as PDFs, and supports tool calling and structured JSON-schema outputs.