Claude Fable 5 vs Claude Sonnet 5.5
Harvey LAB-AA 1.1?
Fable 5—
Sonnet 5.5at max2.8
EBR Bench?
Fable 539.5
Sonnet 5.5—
SpireClimb?
Fable 5—
Sonnet 5.5at max1.3
SpireClimb StS1 A20 Heart?
Fable 5—
Sonnet 5.5at max0
SpireClimb StS2 A10?
Fable 5—
Sonnet 5.5at max2.7
| Benchmark | Fable 5 | Sonnet 5.5 |
|---|---|---|
| AutomationBench-AA | 54.1 | 59.4 |
| GDPval-AA (work tasks) 2.1 | 1,609.9 | 1,558.1 |
| AA Analyst Agent | 48.8 | 57.5 · max |
| Terminal-Bench 4.0 | 42.4 | 43.9 |
| AA-Briefcase 1.1 · Elo | 1,536.9 | 1,634.1 |
| AA-LCR (long context) 1.1 | 82.3 | 78 |
| DeepSWE 1.1 | 69.7 | 70.5 · max |
| Furniture Assembly | 35.8 | 75 · max |
| τ³-bench · banking · 1.0.1 | 39.7 | — |
| τ³-Banking · AA | 38.1 | — |
| Terminal-Bench Hard (version unstated) | 62.9 | — |
| Terminal-Bench Science 0.1 | — | 34.3 |
| EnterpriseOps-Gym-AA | 51.1 | — |
| FrontierCode 1.1 | — | 44.3 |
| Harvey LAB-AA 1.1 | — | 2.8 · max |
| SWE-bench Pro (v2 full) | — | 95.8 · xhigh |
| SWE-bench Pro (v2 hard) | — | 70.6 · xhigh |
| EBR Bench | 39.5 | — |
| SpireClimb | — | 1.3 · max |
| SpireClimb StS1 A20 Heart | — | 0 · max |
| SpireClimb StS2 A10 | — | 2.7 · 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.