The 39.3M ablation was the critic's worst ground. At a matched 131M budget:
both-seat training is worth +17.1 points of win rate, the privileged critic
+3.7 -- a 4.6x gap. And they behave differently: both-seat is flat across scale
(+16.8 at 39.3M, +17.1 at 131M) while the critic swings (-1.6 to +3.7).
The mechanism explains it. Both-seat doubles the data at the same compute --
self-play already played those plies with the same network. The critic adds no
data, only accuracy, and a privileged value trunk has more to fit, so it grades
badly until there is enough to fit it with.
Fable ranked the critic first among missing ideas and both-seat fourth. That was
exactly backwards.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01XBQKgvBbxbheiTF1AVy1Sh
coolguyandClaude Opus 4.8
cc12b058e5