Vercel AI Gateway Adds Claude Fable 5, Anthropic's Mythos-Class Model

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Vercel has made Anthropic's Claude Fable 5, a Mythos-class model, available on its AI Gateway. This integration provides developers with access to a highly capable AI for complex, multi-step tasks without requiring separate provider accounts.

Vercel has integrated Anthropic's Claude Fable 5 into its AI Gateway, offering developers a unified API to access the new "Mythos-class" model. Fable 5 represents a notable advancement over prior Claude models, particularly for long-running, ambiguous, and multi-step tasks that previously required frequent human oversight.
Model Identifier
anthropic/claude-fable-5
Data Retention
Prompts and completions retained for 30 days (not used for training)
Misuse Safeguards
Blocking classifiers for offensive cybersecurity, biology, summarized-thinking extraction
AI Gateway Pricing
No markup over provider pricing, no platform fee on inference

This model is designed to sustain productive output across multi-day runs and reliably manage parallel sub-agents. Its capabilities in areas like code review, bug-finding, and repository investigation are stronger, with higher first-shot correctness on complex problems. Anthropic has implemented blocking classifiers to refuse outputs in offensive cybersecurity, biology, and summarized-thinking extraction due to potential misuse risks.

Claude Fable 5 is available on AI Gateway with no markup over provider pricing, and Vercel does not charge a platform fee on inference. To use the model, set the model identifier to anthropic/claude-fable-5 in the AI SDK. This release builds on Anthropic's earlier work with Claude Mythos Preview, which was initially restricted due to autonomous cyberattack risks, and follows the general availability of Claude Fable 5 from Anthropic.

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Claude Fable 5 is now on AI Gateway. A Mythos-class model for your hardest unsolved problems. ๐š–๐š˜๐š๐šŽ๐š•: '๐šŠ๐š—๐š๐š‘๐š›๐š˜๐š™๐š’๐šŒ/๐šŒ๐š•๐šŠ๐šž๐š๐šŽ-๐š๐šŠ๐š‹๐š•๐šŽ-๐Ÿป' https://t.co/oLvVc2UvaE

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Still wondering? A few quick answers below.

Claude Fable 5 is a "Mythos-class" AI model from Anthropic, now available through Vercel's AI Gateway. It is designed for complex, multi-step tasks, offering improved performance in areas like code review and bug-finding compared to previous Claude models.

Anthropic describes Mythos-class models as exceeding the capabilities of their generally available predecessors, particularly in handling long-running, ambiguous tasks and coordinating sub-agents. Fable 5 includes safeguards to prevent misuse in sensitive domains.

Developers can access Claude Fable 5 by setting the model to anthropic/claude-fable-5 within the AI SDK. Vercel's AI Gateway provides a unified API for calling models, tracking usage, and configuring optimizations without additional platform fees.

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