Claude Fable 5.1 keeps Claude Fable 5's $10 input and $50 output price per million tokens, but cuts prompt-cache reads from $1.00 to $0.25 per million, a 75% drop. Anthropic released it on September 1, 2026 as claude-fable-5-1, aimed at long-running agentic coding, multistep research and document, spreadsheet and slide work.
For anyone weighing claude fable 5.1 vs claude fable 5, the price sheet, three breaking API changes and the Arena numbers below cover the upgrade decision.
Claude Fable 5.1 vs Claude Fable 5
Rates from Anthropic's pricing page, USD per million tokens:
| Item | Claude Fable 5.1 | Claude Fable 5 |
|---|---|---|
| Input | $10 | $10 |
| Output | $50 | $50 |
| 5-minute cache write | $12.50 | $12.50 |
| 1-hour cache write | $20 | $20 |
| Cache read | $0.25 | $1.00 |
| Batch input / output | $5 / $25 | $5 / $25 |
Cache reads on Fable 5.1 cost 2.5% of the base input price, against 10% on most Claude models and 5% on Claude Opus 5.5 and Claude Sonnet 5.5. Writes are unchanged, so the saving shows up in agents that keep re-reading the same repository, tool definitions and conversation history.
Specifications
The model overview lists a 1M-token context window, 128K max output, always-on adaptive thinking with high as the default effort, text and image input, and a June 2026 knowledge cutoff. It runs on the Claude API, Amazon Bedrock, Google Cloud, Microsoft Foundry and Claude Platform on AWS, with retirement no sooner than September 1, 2027.
Anthropic still steers most workloads to Claude Opus 5.5 ($4 / $20) and positions Fable 5.1 for demanding reasoning, or for cases where Opus 5.5 at higher effort falls short. Claude Mythos 5.1 has the same capabilities and pricing but is limited to organizations in Anthropic's verification programs.
Migration Changes
Three changes break existing Fable 5 integrations: forced tool use now returns an error, only Fable 5.1 and Mythos 5.1 can read Fable 5.1 thinking blocks, and editing earlier turns invalidates thinking blocks. The additive changes are per-message effort (beta), turn-scoped system messages (beta), readable progress updates between tool calls (display: "updates", beta), the cheaper cache read, and content provenance.
Claude Fable Series Timeline
Fable is Anthropic's top tier, priced above Opus. Anthropic's Fable page and model deprecations page give this history:
| Date (2026) | Event |
|---|---|
| June 9 | Claude Fable 5 launches as Anthropic's fifth model generation; claude-mythos-preview is deprecated the same day |
| June 12 | Anthropic announces Fable 5 access is unavailable |
| July 1 | Access to Fable 5 is restored and rolling out |
| August 6 | Fable 5's biology safeguards are updated to cut false positives |
| September 1 | Claude Fable 5.1 launches with cheaper cache reads |
Fable 5 and Fable 5.1 each have a Mythos counterpart (claude-mythos-5, claude-mythos-5-1), reserved for security teams and life sciences researchers who pass Anthropic's verification programs. Fable itself runs with safeguards on, and Anthropic says many biology and cybersecurity queries are answered by Opus models instead. Both claude-fable-5 and claude-fable-5-1 are active, with retirement no sooner than June 9, 2027 and September 1, 2027.
Anthropic has not announced a Claude Fable 5.5. As of October 22, 2026, its models overview lists Fable 5.1 as the current Fable model, next to Opus 5.5, Sonnet 5.5 and Haiku 5.5, and the deprecations page has no Fable 5.5 ID. Third-party posts about a Fable 5.5 rely on unofficial listings, and none gives an Anthropic model ID, price or spec.
Arena and Usage Data
On the Arena overall leaderboard published October 15, 2026, Claude Fable 5 (High) sits at No. 4 with a 1503.6 rating over 42,004 votes, and Claude Fable 5.1 (Max) at No. 6 with 1502.3 over 14,590 votes. The confidence intervals overlap, so human-preference voting does not separate the two yet.
→ Track it on AI Rank: Claude Fable 5.1 (Max) — Arena rating, rank and history
Usage tells a clearer story. On AI Rank's OpenRouter text ranking for October 10–16, 2026, Claude Fable 5.1 (non-batch) ranked No. 51 with about 254B tokens (+16%), while Claude Fable 5 ranked No. 134 with about 25.7B (+3%).
→ Live usage: see the OpenRouter model usage ranking on AI Rank (tokens, Oct 10–16, 2026 window).
Compare before you choose: pricing changes and rankings move daily — check the current model rankings on AI Rank before you commit.
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Prepared with automated editorial assistance and checked against official sources and dated AI Rank data on October 16, 2026; the series timeline and usage figures were added or refreshed on October 22, 2026. We did not run our own benchmarks for this article.