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Anthropic: claude-fable-5.1:free

claude-fable-5.1:free
1M context128K outReasoningToolsVisionFilesCacheStructuredComputer useNative JSON
Released Sep 1, 2026Knowledge cutoff Jun 2026Updated Oct 13, 2026

Claude Fable 5 is a Mythos-class model from Anthropic, built for autonomous knowledge work and coding. It supports text, image, and file inputs with text output, with reasoning support and a 1M-token context window. It is suited for long-running, complex, and asynchronous tasks that previously required frequent human check-ins. It is particularly strong at end-to-end work that would otherwise take a person hours, days, or weeks - taking on problems that are long-running, ambiguous, or highly multi-step. It executes well-scoped tasks with few mistakes, automatically self-correcting through verification loops, and ships with robust safeguards.

Mode chatTokenizer ClaudeReasoning levels maxModeratedDeprecation Dec 2027

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Pricing

Input price
$0.00/ 1M tokens
Output price
$0.00/ 1M tokens
Compatible endpoints openaiVendor Anthropic

Uptime

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Supported parameters

All providers = every upstream serving this model supports it. Some providers = depends on which upstream handles the request. Default = the value sent when you leave the parameter unset.

ParameterProvidersDefault
include_reasoningAll providers-
max_completion_tokensSome providers-
max_tokensAll providers-
reasoningAll providers-
reasoning_effortAll providers-
response_formatAll providers-
stopAll providers-
structured_outputsAll providers-
tool_choiceAll providers-
toolsAll providers-
verbosityAll providers-

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