Chess language-model experiments

Five chess language-model checkpoints and evaluation summaries from experiments in 0xrushi/ChessLFM. These checkpoints are provided for research and reproducibility.

Model lineage: LiquidAI/LFM2.5-230M-Base β†’ public mlabonne/LFM2.5-230M-Chess β†’ four experiments in this repository. The upstream ChessLFM checkpoint records LiquidAI's base model in its surgery_meta.json. Our four experimental checkpoints use the released ChessLFM weights as their direct starting point, so they descend from LiquidAI's base through ChessLFM. They were not trained from random initialization or directly from the LiquidAI base weights. The released-baseline/ folder is the upstream ChessLFM reference, not a model trained by this project.

Checkpoints and observed results

Rank by highest observed score Folder Checkpoint Match score W/D/L Opening block Descriptive Elo*
1 released-baseline/ Released ChessLFM baseline 17.5/32 12/11/9 Later (16–31) ~2033
2 branch-ranking-treatment/ Branch-ranking treatment 15.5/32 12/7/13 Later (16–31) ~1989
3 branch-ranking-control/ Matched branch-ranking control 13/32 5/16/11 Later (16–31) ~1934
4 (tie) self-play-refresh/ Self-play refresh, round 1 12/32 9/6/17 Initial (0–15) ~1911
4 (tie) action-value-finetune/ Action-value fine-tune, standard search 12/32 10/4/18 Initial (0–15) ~1911

*The Elo column applies the logistic score transform relative to Stockfish configured at Elo 2000. It is descriptive only: 8–32 games per condition gives substantial uncertainty. Opening blocks differ, so ranks across blocks are only an ordering of the highest observed scores, not a controlled cross-model comparison. In the later block, the paired bootstrap interval for branch-ranking treatment versus control was [βˆ’4.0, +9.5] points; it includes no advantage. See the detailed experiment report.

What is included

Each folder contains Transformers model weights, model configuration, the chess tokenizer, and token_ids.json. Training recovery states, optimizer files, raw datasets, and match journals are not included. Use the project code for the chess-specific 80-token prompt, legal-move masking, and depth-three search; these weights alone are not a complete chess engine.

Example loading one checkpoint:

from transformers import AutoModelForCausalLM, AutoTokenizer

repo = "0xrushi/chesslfm-experiments"
subfolder = "released-baseline"
tokenizer = AutoTokenizer.from_pretrained(repo, subfolder=subfolder)
model = AutoModelForCausalLM.from_pretrained(repo, subfolder=subfolder)

License

The model weights are derivatives of LiquidAI/LFM2.5-230M-Base through the upstream ChessLFM checkpoint. They are distributed under the LFM Open License v1.0, including its commercial-use threshold. The repository's training code is separately available under MIT in the GitHub project.

References

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