Same API price, but Fable 5.1 costs nearly 3x more than Fable 5 on MineBench
ENT_Alam · reddit · 2026-09-03
The maintainer of MineBench (a Minecraft-building model benchmark) compared Fable 5 vs Fable 5.1 and found a hidden cost spike despite unchanged API pricing: 15 builds cost $147.55 vs $54.93 (nearly 3x), with average inference time doubling from 18m to 40m — largely from substantially longer reasoning. Average JSON size (34 MiB) was comparable.
Even so, Fable 5.1 remains far cheaper than GPT 5.6 Sol P, the current leaderboard top model. Style notes: some 5.1 builds (e.g., the Astronaut) feel closer to Opus 5, raising curiosity (and worry) about whether its coding behavior drifts that way too. Fable 5.1 was also the first model to create genuinely recognizable interiors — a cottage with a bed, table, bookshelf, and fireplace, shown in an official demo video. MineBench now lets you explore any build in the voxelBox viewer; full release notes are on GitHub v4.0.0.
Related event: Claude Fable 5.1 tops benchmarks but sparks cost controversy(34 posts)→
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