Anthropic's standard-safeguard flagship, released September 1, 2026. Claude Fable 5.1 pairs the same base model behind the invitation-only Mythos 5.1 with a lighter safeguard configuration, and scores 66 on Artificial Analysis's Intelligence Index — the highest the service has recorded (Opus 5: 63, GPT-5.6 Sol: 61). Pricing holds at $10/$50 per million tokens while cache reads drop 75% to $0.25, which materially lowers the cost of long agent runs and context-heavy knowledge work. It offers a 1M-token context window with 128K max output.
Parameters
Undisclosed
Context Window
1M
License
Proprietary
Release Date
2026-09-01
API Pricing
Input Price (per 1M tokens)
$10
Output Price (per 1M tokens)
$50
Billing Mode: standard
Strengths
- •Highest Intelligence Index ever recorded on Artificial Analysis (66; Opus 5: 63, GPT-5.6 Sol: 61)
- •Cache reads cut 75% to $0.25, lowering the real cost of long agent runs
- •Frontier base model (shared with Mythos 5.1) in a broadly available safeguard configuration
- •1M context and 128K output make it a drop-in upgrade for existing Claude pipelines
Weaknesses
- •Standard token pricing unchanged at $10/$50, so one-shot workload costs do not improve
- •June 2026 knowledge cutoff predates fast-moving fall events
- •Safeguard split with Mythos 5.1 complicates cross-product benchmark comparisons
- •Index and benchmark figures remain vendor-associated pending independent confirmation
Use Cases
- •Research and analysis agents that reuse long contexts across many turns
- •Multi-file code refactoring and software engineering
- •Document-heavy knowledge work (legal, financial, compliance)
- •Performance upgrades to existing Claude-based agent pipelines
Deep Analysis
AA Intelligence Index
66
Highest recorded; Opus 5: 63, GPT-5.6 Sol: 61
Context Window
1M tokens
128K max output; model ID claude-fable-5-1
API Price
$10 / $50 per 1M
Cache reads cut 75% to $0.25 per 1M — the real saving on long agent runs
Release
September 1, 2026
Same base as invitation-only Mythos 5.1; lighter safeguard configuration
Terminal-Bench-Science 0.1
52.6%
Vendor-reported scientific terminal task score
Strengths
- ・The highest Artificial Analysis Intelligence Index ever recorded (66), ahead of Opus 5 (63) and GPT-5.6 Sol (61).
- ・Cache-read price cut of 75% (to $0.25 per 1M tokens) materially lowers the cost of long multi-turn agent runs.
- ・Ships as the standard-safeguard twin of Mythos 5.1 — frontier capability with a more permissive, widely available safety configuration.
- ・1M context and 128K output keep it a drop-in upgrade for existing Claude agent pipelines.
Weaknesses
- ・No price drop on standard tokens ($10/$50), so headline cost is unchanged for one-shot workloads.
- ・The June 2026 knowledge cutoff predates the fast-moving events of the fall.
- ・Safeguard-config split with Mythos 5.1 means 'the same model' can behave differently across the two products, which complicates benchmark comparisons.
- ・Intelligence Index and Terminal-Bench-Science figures remain vendor-associated and need independent confirmation.
Competitor Comparison
| Model | Arena | SWE | GPQA | Price |
|---|---|---|---|---|
| Claude Fable 5.1 | 66 (AA Intelligence Index) | N/A | N/A | $10/$50 |
| Claude Opus 5 | 63 (AA Intelligence Index) | N/A | N/A | $15/$75 |
| GPT-5.6 Sol | 61 (AA Intelligence Index) | N/A | N/A | $5 input |
| GPT-6 Astra | 72.6% (OSWorld 2.0) | 57.9% (Terminal-Bench 4.0) | 97.6% (FrontierMath T4) | $10/$50 |
Claude Fable 5.1, released September 1, 2026, is Anthropic's standard-safeguard edition of the same base model behind the invitation-only Mythos 5.1. Artificial Analysis scores it 66 on its Intelligence Index — the highest the service has recorded — while pricing holds at $10/$50 per million tokens and cache reads drop 75% to $0.25. It is the strongest broadly available Claude configuration to date.
Sources
Analysis generated: 2026-09-04