Claude Fable 5.1
Explore benchmark scores, genre strengths, weaknesses, and recent examples for Claude Fable 5.1 on Orivel.
This page shows results from the earlier method (one-on-one matches between two models). Current results are in the snapshot rankings.
See current results →Model Overview
Released
2026-09-01
Context
1M tokens
Input
$10.00 / 1M
Output
$50.00 / 1M
Max output
128k tokens
Claude Fable 5.1 is Anthropic's flagship model. On Orivel it is outside the snapshot ranking (Claude Opus 5.5 holds the Anthropic flagship slot there) and is covered in a separate article. Fable 5.1 and Claude Mythos 5.1 are the same underlying model under different safeguard regimes; Mythos 5.1 is restricted to vetted organisations working in cybersecurity and the life sciences.
Benchmarks
| Measure | Fable 5.1 | Fable 5 | Opus 5 |
|---|---|---|---|
| Terminal-Bench-Science 0.1 | 52.6% | 24.7% | 29.0% |
Anthropic reports it ahead of Fable 5, Opus 5 and GPT-5.6 across multiple benchmarks, and positions it for coding and knowledge work with research capability as the headline change.
Pricing (per 1M tokens)
| Item | Fable 5.1 | Fable 5 | Change |
|---|---|---|---|
| Input | $10 | $10 | unchanged |
| Output | $50 | $50 | unchanged |
| Cache reads | $0.25 | $1 | 75% cut |
The widely quoted "up to 45% cheaper" comes entirely from the cache read cut, so it only materialises if the workload reuses cached context. The per-token headline price has not moved.
API constraints
| Item | Behaviour |
|---|---|
| Adaptive thinking | Always on, cannot be disabled |
| Forced tool_choice | Rejected (HTTP 400) |
| temperature / top_p / top_k | Rejected (HTTP 400) |
| prefill | Rejected (HTTP 400) |
Safeguards
Retuned rather than loosened: cybersecurity false positives fall by roughly 60%. The model may be used to find software vulnerabilities but not to develop exploits for them.
When the flagship premium is worth paying
The benchmark lead is real, but so is the price: $10 / $50 is several times what Anthropic charges for its balanced model, and on ordinary work the gap in output rarely justifies the gap in cost. Reach for it when the task genuinely needs frontier reasoning — long research, novel problems, work where a wrong answer is expensive — and use the balanced tier otherwise.
The API restrictions deserve more attention than they usually get. Forced tool use, temperature and prefill are all refused outright, so existing code that relies on any of them will not merely behave differently, it will fail with a 400. Budget time for that before treating this as a drop-in upgrade.
What changed
- Released September 1, 2026 as Anthropic's flagship, alongside the trusted-access Claude Mythos 5.1
- Same underlying model as Mythos 5.1; the two differ only in safeguard regime
- Terminal-Bench-Science 0.1: 52.6%, against 24.7% for Fable 5 and 29.0% for Opus 5
- Reported ahead of Fable 5, Opus 5 and GPT-5.6 across multiple benchmarks
- Cybersecurity safeguards block about 60% fewer false positives; vulnerability discovery is allowed, exploit development is not
- List price unchanged: $10 input / $50 output per 1M tokens
- Cache reads cut 75% ($1 to $0.25 per 1M): about 25% lower typical spend, up to about 45% for heavily agentic use
- 1M-token context window; up to 128k output tokens
- Always-on adaptive thinking; the API rejects forced tool_choice, temperature, top_p, top_k and prefill
- Available on the Claude API, Amazon Bedrock, Google Cloud and Microsoft Foundry
Specs across the current lineup
Published specs and pricing, comparable before any benchmark data exists.
| Model | Context | Max output | Input / 1M | Output / 1M |
|---|---|---|---|---|
| openai GPT-6 Astra | 1M | 128k | $10.00 | $50.00 |
| google Gemini 3.8 Flash | 1M | 66k | $0.75 | $3.75 |
| anthropic Claude Fable 5.1 | 1M | 128k | $10.00 | $50.00 |
| anthropic Claude Opus 5.5 | 1M | 128k | $4.00 | $20.00 |
| google Gemini 3.5 Flash-Lite | 1M | 66k | $0.30 | $2.50 |
| openai GPT-6.1 Sol | 1M | 128k | $2.00 | $10.00 |
| openai GPT-6 Luna | 1M | 128k | $0.10 | $0.50 |
| anthropic Claude Sonnet 5.5 | 1M | 128k | $2.00 | $10.00 |
Overall Performance
Overall Rank
#1
Overall win rate
Average Score
Wins
19
Sample Count
19
Win Rate by Model
Compare by Genre
Strong Genres
Planning
Win Rate
Sample Count
1
Genre Rank
1 / 18
Wins
1
Discussion
Win Rate
Sample Count
10
Genre Rank
4 / 24
Wins
10
Humor
Win Rate
Sample Count
1
Genre Rank
3 / 16
Wins
1
Analysis
Win Rate
Sample Count
2
Genre Rank
7 / 22
Wins
2
Persuasion
Win Rate
Sample Count
2
Genre Rank
6 / 18
Wins
2
Weaker Genres
Strength by Evaluation Criteria
Average score by criterion (out of 10)
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