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Claude Fable 5.1 (Anthropic) is the successor to Claude Fable 5 in Tess — same input/output price, cheaper cache reads, and stronger long-running agents, multistep research, and document / spreadsheet / slide work. Released 1 September 2026.

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What changed vs Claude Fable 5

Native reasoning, tools, and image input. Anthropic’s public Fable line — reserve it for work that still falls short on lighter Claude models.
Anthropic classifies Fable 5.1 as a Covered Model: extra retention and safety review on the provider side. Follow the Tess Privacy Policy and Anthropic’s retention guidance. Don’t send secrets, credentials, or regulated personal data unless the task needs them.

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Pricing (Tess credits)

Values follow Models and Costs (credits per 100 tokens). Same input/output as Fable 5 — Anthropic did not change headline rates: Long agent sessions that re-read a cached prefix are cheaper on the provider (cache reads at a quarter of Fable 5). Keep the thread on 5.1 to take advantage of that.
Screenshot placeholder — model picker: Capture the chat model selector with Claude Fable 5.1 selected.

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Ideal use cases in Tess

  1. Long-running coding agents — features across a codebase, review, and performance work that spans many steps
  2. Multistep research that has to keep the plan through tool calls
  3. Knowledge work on documents, spreadsheets, and slides in one thread
  4. Hard reasoning where Fable 5 (or a lighter Claude) still falls short
  5. 1M-context sessions without switching models
Best practices
  • Thinking cannot be turned off. Default effort is high — don’t use Fable 5.1 as a cheap extractor.
  • Prefer Fable 5 only if you already have a working flow and don’t need the 5.1 agent/research gains; price per token is the same, cache is more expensive on 5.
  • Treat long chats as append-only. Editing earlier turns can drop or invalidate thinking blocks on the provider.
  • Cap response length in the prompt when you don’t need a long deliverable.
See also: Claude Fable 5 · Models and Costs · Claude Fable 5.1 (Anthropic).