The meaningful difference
Sol reports strong efficiency and broad frontier capability; Fable emphasizes sustained autonomous work but has higher list prices and sensitive-domain routing.
Choose by workload
Choose GPT-5.6 Sol when your priority is maximum cross-domain reasoning and OpenAI agent tooling. Its relevant strengths include frontier agentic and coding results and million-token long-context evaluations.
Choose Claude Fable 5 when your priority is long-running coding and professional knowledge-work agents. Account for premium token pricing before committing.
Specification comparison
| Measure | GPT-5.6 Sol | Claude Fable 5 |
|---|---|---|
| Access | API + app | API + app |
| License | Proprietary | Proprietary |
| Context | 1.0M | 1.0M |
| Provider-listed API input / 1M | $5.00 | $10.00 |
| Provider-listed API output / 1M | $30.00 | $50.00 |
| MMLU-Pro | — | — |
| GPQA Diamond | 94.6 | 92.6 |
| SWE-bench Verified | — | — |
| LiveCodeBench | — | — |
| SWE-Bench Pro | 64.6 | 80 |
| Artificial Analysis Intelligence Index | 58.9 | 59.9 |
A fair test for this pair
Run a week-long shadow evaluation across your hardest coding and knowledge tasks, including retries, reviewer time, refusal rates, and total accepted-output cost.
Bottom line: use reported results to form a hypothesis, then make the decision with representative private tasks. Missing scores remain missing; no composite winner is manufactured.