benchrAnthropic
Claude Fable 5.1
Anthropic · frontier. Production agentic coding with a 1M-token context window.
The published record
Every number below was read from the provider's own documentation on the date shown. benchr does not restate a figure it has not seen published.
- API identifier
claude-fable-5-1- Context window
- 1MtokensSource
- Maximum output
- 128KtokensSource
- Input
- $10.00per 1M tokensSource
- Output
- $50.00per 1M tokensSource
- Cached input
- $0.25per 1M tokensSource
- Released
- September 1, 2026Source
- License
- Proprietary
Availability Generally available through the Claude API and Anthropic's supported cloud platforms. Adaptive thinking is always on.
Record verified September 2, 2026
What the record says
Released September 1, 2026. Fable 5.1 is a new API ID, not an alias for Fable 5. Anthropic documents that tool_choice type any and named-tool forcing return HTTP 400; auto and none are valid. Manual or disabled thinking configuration is not supported because adaptive thinking is always on. Assistant prefills are unsupported. Fable 5.1 is not supported on Priority Tier. Anthropic states that 30-day data retention normally applies; zero-data-retention access requires authorization.
What has moved
Entries in the change ledger that affect this model, newest first.
Released
Anthropic released claude-fable-5-1 on September 1, 2026. Official docs list 1M context, 128K max output, $10/$50 standard input/output per 1M, $0.25 cached input, and Batch at $5/$25. Adaptive thinking is always on. Source: anthropic.com/claude-fable-and-mythos-5-1 and platform.claude.com/docs/en/models/fable-5-1/overview (verified 2026-09-02).
Which one to use
The rest of the family, with the two numbers that usually decide it. The current model is marked.
| Models | Input | Output | Context window |
|---|---|---|---|
| Claude Haiku 4.5 | $1.00 | $5.00 | 200K |
| Claude Sonnet 5 | $2.00 | $10.00 | 1M |
| Claude Sonnet 4.6 | $3.00 | $15.00 | 1M |
| Claude Opus 4.7 | $5.00 | $25.00 | 1M |
| Claude Opus 4.8 | $5.00 | $25.00 | 1M |
| Claude Opus 5 | $5.00 | $25.00 | 1M |
| Claude Fable 5 | $10.00 | $50.00 | 1M |
| Claude Fable 5.1 This page | $10.00 | $50.00 | 1M |
benchr's read
Worth it for
- Production agentic coding with a 1M-token context window
- Repeated-prefix workloads where $0.25 per 1M cache reads materially change cost
- Fable 5 migrations whose tool choice remains auto or none
- Long-running assistant workflows that can use adaptive thinking
Look elsewhere if
- Your client forces tool_choice type any or a named tool — the 5.1 API returns HTTP 400
- You require Priority Tier — Anthropic does not support Fable 5.1 on it
- You require zero-data-retention access without Anthropic authorization
- You expect a published Fable 5.1 score in the tool's normalized benchmark columns
Prices, limits, and identifiers above are provider facts. This section is benchr's judgement about them.
What benchr has written about it
Pieces that name this model, newest first. The ones written about this model come before the ones that mention it in passing.
What is not on this page
Stated rather than filled in.
- No first-token or tokens-per-second figure is recorded. benchr has not measured it and the provider does not publish one.