English

Not all Chess960 positions are equally complex

Physics and Society 2026-03-10 v3 Disordered Systems and Neural Networks Human-Computer Interaction

Abstract

We analyze strategic complexity across all 960 Chess960 (Fischer Random Chess) starting positions. Stockfish evaluations reveal a near-universal first-move advantage for White (E=+0.33±0.12\langle E \rangle = +0.33 \pm 0.12 pawns), indicating that the initiative is a robust structural feature of the game. To quantify decision difficulty, we introduce an information-based measure S(n)S(n) that captures the cumulative information required to identify optimal moves over the first nn plies. This measure decomposes into White and Black contributions, SWS_W and SBS_B, defining a total opening complexity Stot=SW+SBS_{\mathrm{tot}} = S_W + S_B and a decision asymmetry A=SBSWA = S_B - S_W. Across the ensemble, StotS_{\mathrm{tot}} ranges from 2.62.6 to 17.217.2 bits, while AA spans from 4.5-4.5 to +4.2+4.2 bits (mean A=0.26\langle A \rangle = -0.26), showing that openings are nearly evenly split between those that burden White and those that burden Black, with a slight average excess complexity for White. Standard chess (position \#518, \texttt{RNBQKBNR}) exhibits near-average total complexity and asymmetry, yet lies far from the configuration that jointly minimizes evaluation imbalance and decision asymmetry. These results reveal a highly heterogeneous Chess960 landscape in which small rearrangements of back-rank pieces can substantially alter strategic depth and competitive balance. The classical starting position--despite centuries of refinement--appears not as an extremum, but as one configuration among many in a broad statistical ensemble.

Cite

@article{arxiv.2512.14319,
  title  = {Not all Chess960 positions are equally complex},
  author = {Marc Barthelemy},
  journal= {arXiv preprint arXiv:2512.14319},
  year   = {2026}
}

Comments

Final version (revised and corrected), 11 pages, 9 figures

R2 v1 2026-07-01T08:27:13.454Z