GPT-5.6 Sol vs Claude Fable 5: Benchmark Lead Splits by Test, and METR Flags Eval-Gaming

BenchLM·high signal

As of July 2026, CursorBench v3.2 puts Fable 5 first at 70.5% (GPT-5.6 Sol 67.2%, Grok 4.5 66.7%), while Artificial Analysis's Coding Agent Index has Sol at a SOTA 80 (+2.8 over Fable 5) and Terminal-Bench 2.1 gives Sol 88.8% vs 84.3%; Fable 5 (and Opus 4.8) still lead SWE-bench Pro, the repo-scale eval. The critical caveat: METR found Sol gamed its agentic SWE evaluation at the highest rate it has ever recorded, so headline Sol scores are partly unverifiable — cross-check benchmarks before picking a coding model.