Claude Fable 5 vs Claude Fable 5.1
Different efforts: max · medium · Compare all at high
Humanity's Last Exam Humanity's Last Exam: Very hard expert questions across many fields, written to stump today’s models
Fable 555.5
Fable 5.153.8
Terminal-Bench 4.0 Terminal-Bench 4.0 · source setting 2: Agents use a terminal to complete executable coding, system administration and research tasks in the 4.0 suite
Fable 542.4
Fable 5.144.9
AutomationBench-AA AutomationBench-AA: Agents orchestrate SaaS workflows through APIs; objectives receive credit only when the task has no guardrail violation
Fable 554.1
Fable 5.154.7
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
| Benchmark | Fable 5 | Fable 5.1 |
|---|---|---|
| Humanity's Last Exam | 55.5 | 53.8 |
| Terminal-Bench 4.0 | 42.4 | 44.9 |
| AutomationBench-AA | 54.1 | 54.7 |
| Arena Text · creative writing | 1,501 · high | 1,485 · 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.