Hands-On Ranking: Fable 5.1 Beats Claude Opus on RL Environment Creation

HarveenChadha · x · 2026-09-03

The author finds Fable 5.1 a next-level model that works very well on RL environment creation/ideation tasks. Returning to Opus 5 after a long time, it has also improved a lot, though what's happening under the hood remains hard to understand. His ranking: F5.1 > F5 > 5.6 sol > Opus 4.8.

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