Fable 5.1 on Frontier Coding Tasks: Efficient Successes, Distinct Failure Modes

We evaluated Fable 5.1 on a series of frontier coding tasks from our proprietary Terminal-Bench+ dataset and compared the results against Opus 5. Fable remained competitive across most categories and was materially more efficient on successful runs, while its gap was concentrated in a small set of terminal-heavy and build/dependency tasks. Because category sizes are small and uneven, we treat the category results as descriptive of this task set. Fable 5.1 gives you speed with robustness. On the same coding tasks it is dramatically cheaper per successful run than Opus 5 and competitive across most categories, but it loses more attempts outright. On a curated set of tasks undertaken by both…