Claude Fable 5.1 vs Gemini 4 Argon
| Benchmark | Fable 5.1 | Gemini 4 Argon |
|---|---|---|
| Arena Text · creative writing | 1,485 · max | 1,516 |
| Lech Mazur Short-Story | 3.8 · high | 0.8 |
| Harvey LAB-AA 1.1 | 6.4 · max | 3.9 |
| EQ-Bench Longform Creative Writing 1.11 | 85.3 | — |
| EQ-Bench Creative Writing v3 | 2,162 | — |
Specs
| Spec | Fable 5.1 | Gemini 4 Argon |
|---|---|---|
| Input, per 1M | $10 | !$2 |
| Output, per 1M | $50 | !$10 |
| Cost per task? | $2.98 | $1.99 |
| Speed, tok/s | 56 | 84 |
| Context | 1M | 1M |
| Weights | Closed | Closed |
| Released | Sep 2026 | Oct 2026 |
| See images | ✓ | ✓ |
| Read PDFs | 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
Synchronous output stops at 65,536›
With background false, output limits above 65,536 tokens return HTTP 400; stay at or below that limit.
Sampling parameters are ignored›
temperature, top_p and top_k are ignored; remove them from requests.
No explicit caching›
Explicit caching is unavailable; omit explicit cache requests.
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.