Claude Fable 5 vs Claude Fable 5.1
Different efforts: max · medium · Compare all at high
Arena Text · creative writing Arena Text · creative writing: Human pairwise preferences in the stated text vote pool
Fable 5 · high1,501
Fable 5.1 · max1,485
EQ-Bench Longform Creative Writing 1.11 Longform Creative Writing 1.11: Models plan, revise and write a story across eight turns, graded with a writing rubric
Fable 583
Fable 5.185.3
EQ-Bench Creative Writing v3 Creative Writing v3 · Elo: Judge-rated creative writing under the v3 prompt set and pairwise ranking
Fable 51,943.1
Fable 5.12,162
Lech Mazur Short-Story Lech Mazur Short-Story · comparison score: Judges compare stories written to ten required elements; the comparison score can be negative
Fable 5 · high2.9
Fable 5.1 · high3.8
IFBench (instructions) IFBench (instructions): Checks whether the model follows precise formatting and content instructions
Fable 563.5
Fable 5.1—
Harvey LAB-AA 1.1 Harvey LAB-AA 1.1: Legal agents work from case documents; every rubric criterion must pass and material hallucinations receive no credit
Fable 5—
Fable 5.1 · max6.4
| Benchmark | Fable 5 | Fable 5.1 |
|---|---|---|
| Arena Text · creative writing | 1,501 · high | 1,485 · max |
| EQ-Bench Longform Creative Writing 1.11 | 83 | 85.3 |
| EQ-Bench Creative Writing v3 | 1,943.1 | 2,162 |
| Lech Mazur Short-Story | 2.9 · high | 3.8 · high |
| IFBench (instructions) | 63.5 | — |
| Harvey LAB-AA 1.1 | — | 6.4 · max |
Specs
| Spec | Fable 5 | Fable 5.1 |
|---|---|---|
| Input, per 1M | $10 | $10 |
| Output, per 1M | $50 | $50 |
| Cost per task? | $8.75 | $2.98 |
| Speed, tok/s | 67 | 56 |
| Context | 1M | 1M |
| Weights | Closed | Closed |
| Released | Jun 2026 | Sep 2026 |
| See images | ✓ | ✓ |
| Read PDFs | Partial | Partial |
| Hear audio | — | — |
| Watch video | — | — |
| Call tools | ✓ | ✓ |
| Force a tool call | Partial | Partial |
| Return strict JSON | ✓ | ✓ |
| Search the web | ? | ? |
| Run code | ? | ? |
| Use a computer | ? | ? |
What breaks when you switch
Fable 5 → Fable 5.1
Replace forced tool_choice›
Forced tool_choice returns HTTP 400; use auto with an explicit instruction and strict tools, or JSON outputs.
Adaptive thinking is always on›
Disabled thinking or manual budget_tokens returns HTTP 400; omit thinking or use adaptive thinking.
No non-default sampling values›
Non-default temperature, top_p or top_k returns HTTP 400; omit non-default sampling values.
Requires 30-day data retention · Claude API›
A Claude API organization or workspace without 30-day retention receives HTTP 400; configure workspace retention or contact the Anthropic account team.
Thinking blocks bind to conversations›
Where conversation binding is enforced, replaying an invalidated block returns HTTP 400; use the documented drop_block control to continue without it.
No assistant prefill›
Assistant prefill returns HTTP 400; use system prompt instructions instead.
Fable 5.1 → Fable 5
Nothing known.