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Claude Fable 5.1

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anthropic/claude-fable-5-1 · by Anthropic · decoder-only-transformer

Pricing — 1 offering(s)

Anthropic

Input tokens

  • $10.00 / 1M tokens (input) Current 2026-09-23 → present
    Same as Fable 5. The models-overview table shows the same figure. First recorded on this verification date…

    Same as Fable 5. The models-overview table shows the same figure. First recorded on this verification date, so the price is dated from it; the model launched in early September 2026.

Output tokens

  • $50.00 / 1M tokens (output) Current 2026-09-23 → present
    Same as Fable 5. The models-overview table shows the same figure. First recorded on this verification date…

    Same as Fable 5. The models-overview table shows the same figure. First recorded on this verification date, so the price is dated from it; the model launched in early September 2026.

Cache hits and refreshes

  • $0.25 / 1M tokens (cached input) Current 2026-09-23 → present

5-minute cache writes

  • $12.50 / 1M tokens (cache write) Current 2026-09-23 → present

Batch

Batch input tokens

  • $5.00 / 1M tokens (input) Current 2026-09-23 → present

Batch output tokens

  • $25.00 / 1M tokens (output) Current 2026-09-23 → present

Showing the active price and any recorded history. Full pricing history is available via the paid API — see API docs.

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About Claude Fable 5.1

Claude Fable 5.1 was Anthropic's top generally available model until Claude Fable 5.2 launched in November 2026. It was announced in September 2026 alongside Claude Mythos 5.1, a limited-availability model not tracked here. It succeeds Claude Fable 5, which Anthropic now lists as a legacy model. It's a decoder-only transformer with adaptive thinking always on, steered by a five-level `effort` parameter that defaults to high on the Claude API.

List pricing is unchanged from Fable 5 at $10 / $50 per million input / output tokens, but cache reads dropped 75% to $0.25 per million tokens. Anthropic estimates that makes typical workloads about 25% cheaper than on Fable 5, and highly agentic ones up to about 45% cheaper. It has a 1M-token context window and 128K maximum output, and is available on the Claude API, Amazon Web Services, Google Cloud and Microsoft Azure.

Capability profile

How Claude Fable 5.1 rates across core capability dimensions, with the task-level evidence behind each rating.

reasoning Strong

Anthropic positions Fable 5.1 'for demanding reasoning and long-horizon agentic work' (models-overview) and reports higher scores than Fable 5 across its launch charts (HLE with and without tools, Terminal-Bench-Science 0.1). Those are vendor-reported and not recorded as structured scores here; see limitations.

coding Strong

Terminal-Bench 2.1 (89 real terminal tasks; Terminus 2 harness): completes 85.0% — fails roughly 1 task in 7. Terminal-Bench 4.0 (66 long-horizon multi-domain tasks; mini-swe-agent): 58.1%. LiveCodeBench: 90.5%, the top score on that board. Independent (Vals AI; Opus 5 / Opus 4.8 served as refusal fallbacks, and counting those as failures gives 79.0% on 2.1 and 50.0% on 4.0). The launch table's own Terminal-Bench 4.0 figure (55.8%, effort not stated) is vendor-reported.

tool use Strong

Launch table: OSWorld 2.0 77.9% partial / 41.7% strict (vendor-reported, settings not stated). Positioned for long-horizon agentic work.

instruction following Strong
context window Strong

1M-token context window and 128K max output (models-overview table).

multilingual Strong
speed Weak

Comparative latency is listed as 'Slower' in Anthropic's models-overview table, the slowest of the current lineup (Opus 5.5 'Moderate', Sonnet 5 'Fast'). Fast mode isn't offered for Fable 5.1.

cost efficiency Moderate

$10/$50 per MTok, 2.5x Opus 5.5's $4/$20. Cache hits at $0.25/MTok (0.025x base input) make heavily cached, agentic workloads much cheaper than Fable 5: Anthropic estimates ~25% lower cost for typical workloads and up to ~45% for highly agentic ones (vendor claim).

Ratings are estimated — limited independent data is available for this model.

Coding benchmarks

View the full coding benchmark leaderboard →
Benchmark Score Harness Source
terminal-bench-2-1 85.0% 2026-09 terminus-2 📊 leaderboard ↗
livecodebench ↗ 90.5% 2026-09 — 📊 leaderboard ↗
terminal-bench-4-0 58.1% 2026-09 mini-swe-agent 📊 leaderboard ↗

Operator guidance

Superseded by Claude Fable 5.2 (November 2026), which Anthropic sells at $8/$40 against this model's $10/$50; Anthropic now lists Fable 5.1 as a legacy model, still available. Its models overview recommended starting with Claude Opus 5.5 for most workloads and moving to Fable 5.1 only when evals at higher Opus 5.5 effort still fall short, so route here for the hardest reasoning and long-horizon agentic work, not by default. It was the slowest Claude model in Anthropic's lineup and costs 2.5x Opus 5.5 per token, though the cheap cache reads narrow the gap on heavily cached agentic loops. Replaces Claude Fable 5, now legacy.

Use cases

Limitations

Citations