Coda is a rewrite of GoChess in Rust, 100% vibe-coded with Claude Code. The initial implememntation - board representation, search, NNUE evaluation, SIMD, and UCI protocol — was written from scratch in a single session - building on top of the work done in gochess.
Author: Adam Twiss
Coda 0.9.3 what's new?
New network
The headline of this release is a new network trained on a substantially revised recipe — changes to the optimiser, loss shaping, and data sampling, together with a refined multi-stage schedule.
X-ray features removed. Coda's networks carried x-ray attack threat features alongside more conventional direct threats. Ablation tests had consistently shown that disabling them cost a surprisingly large amount of Elo. That result was always hard to reconcile with other strong engines doing perfectly well on direct threats alone, and that discrepancy turned out to be the answer: the incremental-update path for non-xray networks contained a latent defect. With the defect fixed, the ablation reversed sign. The x-ray features had been costing strength (eval improved but by less than the NPS cost), masked by a bug in the very code used to evaluate them. The resulting network now has a smaller input space, a cheaper evaluation, and is measurably stronger.
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