Claude Fable 5 vs Claude Sonnet 5.5
Different efforts: max · high · 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
Sonnet 5.5 · xhigh1,465
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
Sonnet 5.5—
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
Sonnet 5.5—
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
Sonnet 5.5—
IFBench (instructions) IFBench (instructions): Checks whether the model follows precise formatting and content instructions
Fable 563.5
Sonnet 5.5—
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—
Sonnet 5.5 · max2.8
| Benchmark | Fable 5 | Sonnet 5.5 |
|---|---|---|
| Arena Text · creative writing | 1,501 · high | 1,465 · xhigh |
| EQ-Bench Longform Creative Writing 1.11 | 83 | — |
| EQ-Bench Creative Writing v3 | 1,943.1 | — |
| Lech Mazur Short-Story | 2.9 · high | — |
| IFBench (instructions) | 63.5 | — |
| Harvey LAB-AA 1.1 | — | 2.8 · max |
Specs
| Spec | Fable 5 | Sonnet 5.5 |
|---|---|---|
| Input, per 1M | $10 | $2 |
| Output, per 1M | $50 | $10 |
| Cost per task? | $8.75 | $0.88 |
| Speed, tok/s | 67 | 106 |
| Context | 1M | 1M |
| Weights | Closed | Closed |
| Released | Jun 2026 | Sep 2026 |
| See images | ✓ | ✓ |
| Read PDFs | Partial | ✓ |
| Hear audio | — | — |
| Watch video | — | — |
| Call tools | ✓ | ✓ |
| Force a tool call | Partial | — |
| Return strict JSON | ✓ | ✓ |
| Search the web | ? | ✓ |
| Run code | ? | ✓ |
| Use a computer | ? | ✓ |
What breaks when you switch
Fable 5 → Sonnet 5.5
No forced tool use›
Forced tool_choice any or tool returns HTTP 400; remove the forced choice.
Replace disabled thinking›
Disabled thinking returns HTTP 400; use between_tools for the lowest thinking setting.
No manual thinking budgets›
Manual thinking budgets and extra between_tools fields return HTTP 400; remove manual budgets and send between_tools without display, budget_tokens or block_binding.
Remove sampling parameters›
Non-default temperature, top_p or top_k returns HTTP 400; remove these parameters.
No assistant prefill›
A prefilled final assistant turn returns HTTP 400; remove that prefill.
Old computer tool rejected · Claude API / Google Cloud›
The computer_20251124 tool returns HTTP 400 on the Claude API and Google Cloud; use computer_toolset_20260801 there.
Sonnet 5.5 → Fable 5
Nothing known.