maia-chess-onnx-opset15

Maia Chess ONNX Models (Opset 15)

Pre-converted ONNX models of Maia chess neural network weights, downgraded from opset 17 to opset 15 for compatibility with ONNX Runtime Web.

Models

Use maia-<elo>.onnx — the -opset15 files are broken

maia-1100.onnx … maia-1900.onnx (added 2026-09-03) are exports made with lc0's own converter. Use these.

• Input: /input/planes — [batch, 112, 8, 8] float32 (lc0 board encoding)
• Output: /output/policy — [batch, 1858] float32, already in move-vocabulary order, so no policy map is needed
• Output: /output/wdl — [batch, 3] float32, a distribution summing to 1

Verified for all nine: from the starting position Maia-1500 ranks e2e4 (13.1) > d2d4 (12.1) > c2c4 (10.0), and WDL reads [0.50, 0.04, 0.46].

The older maia-<elo>-opset15.onnx files are mis-converted and should not be used. They return a saturated WDL ([1, 0, 0]) and policy logits in the hundreds of thousands, and they do so even for an all-zeros input — their highest-scoring outputs correspond to moves that are not legal in the position. They are kept only so existing links do not 404.

Source

maia-<elo>.onnx: converted from the original CSSLab/maia-chess maia_weights/maia-<elo>.pb.gz with lc0 v0.32.1:

lc0 leela2onnx --input=maia-1500.pb.gz --output=maia-1500.onnx --onnx-data-type=f32

maia-<elo>-opset15.onnx (deprecated): from shermansiu/maia-* (opset 17), via onnx.version_converter.convert_version(model, 15) — this is the step that produced the broken outputs described above.

Used by CrispChess (MIT licensed chess app).

Licence — GPL-3.0-or-later (corrected 2026-08-02)

This repository declared license: other, which obscured a copyleft obligation. The upstream weights, shermansiu/maia-1100, are GPL-3.0-or-later, as is the original source they came from, CSSLab/maia-chess (its LICENSE is GPL-3.0 and its README states "The software is available under the GPL License"). Converting them to ONNX does not relicense them, and neither does re-exporting them with lc0.

GPL-3.0 is viral: anything you distribute that incorporates these weights must itself be offered under GPL-3.0-or-later, with the corresponding source made available. That obligation travels with the file and is a good deal more consequential than a vague other tag suggests, which is why it is stated plainly here.