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Anthropic

Claude Fable 5

Claude Fable 5 is Anthropic's most capable widely released model, built for the most demanding reasoning and long-horizon agentic work. Claude Fable 5 runs long, complex, and asynchronous tasks with fewer check-ins and is available on AI Gateway via anthropic, vertexAnthropic with adaptive thinking and configurable effort.

ReasoningTool UseExplicit CachingFile InputVision (Image)
index.ts
import { streamText } from 'ai'


const result = streamText({
  model: 'anthropic/claude-fable-5',
  prompt: 'Why is the sky blue?'
})
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Frequently Asked Questions

  • What is Claude Fable 5 built for?

    Claude Fable 5 is Anthropic's most capable widely released model, built for the most demanding reasoning and long-horizon agentic work. Claude Fable 5 handles long-running, complex, and asynchronous tasks where previous models needed more frequent check-ins.

  • How does thinking work on Claude Fable 5?

    Adaptive thinking is the only thinking mode, and Claude Fable 5 decides how deeply to reason per request. Control depth and cost with the effort parameter. Raw chain of thought is never returned; set thinking.display to summarized for a readable summary.

  • What happens when Claude Fable 5 declines a request?

    The response returns stop_reason: "refusal" as a successful response, not an error, and reports which classifier declined. Configure fallback models with providerOptions.gateway.models and AI Gateway retries the request on the next model in your list, such as Claude Opus 4.8 or Claude Sonnet 5, on every API format.

  • What agent tooling does Claude Fable 5 support?

    At launch, Claude Fable 5 supports the memory tool, code execution, programmatic tool calling, compaction, tool result clearing through context editing, and vision input. Effort control ships as standard, and task budgets are available in beta.

  • What context window and output limit does Claude Fable 5 have?

    Claude Fable 5 has a context window of 1M tokens and supports up to 128K tokens output tokens per request, enough for large codebases, long document sets, and extended agent histories.

  • Does AI Gateway support Zero Data Retention for Claude Fable 5?

    Zero Data Retention is not currently available for this model. Anthropic does not offer Zero Data Retention for Claude Fable 5 because some misuse patterns are only visible across cumulative requests. Prompts and completions are retained for 30 days and are not used to train Claude. Zero Data Retention is offered on a per-provider basis. See https://vercel.com/docs/ai-gateway/capabilities/zdr for details.

  • What is the pricing for Claude Fable 5?

    AI Gateway mirrors provider pricing with no markup and adds no platform fee on inference. Rates are listed on this page and shift when providers update their pricing.

  • How do I call Claude Fable 5 through AI Gateway?

    Set the model to anthropic/claude-fable-5 in the AI SDK, Chat Completions API, Responses API, Messages API, or other API formats, from TypeScript or Python. AI Gateway handles authentication, retries, and failover across anthropic, vertexAnthropic.