Opus 5.5 is probably still nerfed

2026-11-13

A few days ago, I wrote about Opus 5.5 being nerfed. One theory was that this was because of testing Fable 5.2, so I wanted to check again, since Fable has now launched.

Here’s a chart of Opus 5.5’s reported reasoning tokens per request, relative to alternative models in the same battles. The vertical line is the Fable release date, November 9:

Opus 5.5 reasoning relative to matched opponents through November 12, with a vertical line at Fable’s November 9 launch and confidence intervals

From our data alone, we can only say that it’s likely that Opus is still nerfed. The p-val on the bootstrap test of before and after the Fable launch is p=0.105.