Model · Anthropic · Text
Claude Fable 5.1
Anthropic's most capable widely released model — the top tier above Opus 5, built for long-running agentic coding, knowledge work, and research. Succeeds Claude Fable 5.
- Modality
- Text
- License
- Proprietary (Proprietary)
- Context window
- 1,000,000 tokens 1M tokens as both default and maximum, at standard per-token pricing across the whole window, with up to 128k output. Cache reads cost 0.025x the base input price (versus 0.1x on other Claude models). Not covered by the 300k-output batch beta.
- Released
- September 1, 2026
- Last verified
- September 8, 2026
- Runs locally
- No
- Also handles
- vision
Strengths
- Agentic coding over long sessions — multi-file features, large refactors and migrations, debugging and code review across runs lasting hours
- Knowledge work with documents, spreadsheets, and slides, taking an analysis from first question to finished artifact
- Long-context work — reasoning over and connecting details across the full 1M-token window
- Cache reads at 0.025x input ($0.25 per MTok) — a quarter of the 0.1x multiplier every other Claude model charges
Weaknesses
- Most expensive Claude tier ($10/$50 per MTok) — double Opus 5
- No forced tool use: `tool_choice` set to `any` or a named tool returns a 400 error
- Parallel tool calling is more variable than Fable 5 — often one tool call per turn, costing extra round trips and wall-clock time
- At `low` effort it answers from memory more often, calling search and retrieval tools less
- 30-day data retention; not available under zero data retention without express Anthropic authorization
- Closed weights — cannot be self-hosted
Try it
| Where | Type | Notes |
|---|---|---|
| Anthropic API | hosted-api | API key required |
| AWS Bedrock | hosted-api | Enterprise / regional |
| Google Vertex AI | hosted-api | GCP integration |
| Claude.ai | product | Paid plans (Pro and above) |
Version history
- Claude Haiku 5.5 Oct 2026
- Claude Sonnet 5.5 Sep 2026
- Claude Opus 5.5 Sep 2026
- Claude Fable 5.1 Sep 2026 Current
- Claude Mythos 5.1 Sep 2026
Official sources
- Model docs docs
- What's new in Fable 5.1 docs
- Announcement announcement
- System card paper
Change log
- — Initial entry. Released 2026-09-01 as the successor to Claude Fable 5, at the same $10/$50 per MTok with cache reads cut to $0.25 per MTok. Adds adaptive thinking always on; drops support for forced tool use.
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