Claude Fable 5.2 is Anthropic's generally available, production-safeguarded model for demanding reasoning and long-horizon agentic work, sharing underlying weights with Claude Mythos 5.2. Typical uses include agent sessions that run for hours, multistep deep research, and analysis carried through to a finished document, spreadsheet, or deck. It accepts text, images, and files and returns text, with a 1M-token context window and up to 128K output tokens. Adaptive thinking is always on, with the effort parameter controlling reasoning depth (low, medium, high, xhigh, max; default: high). Forced tool use returns an error, and temperature, top_p, and top_k should be omitted. It is priced 20% below Claude Fable 5.1 and offers an optional fast mode with up to 2.5x faster output at 2x the standard price.
anthropic/claude-fable-5.2Nov 9, 2026