R1 — Imitation (SFT)

Part of a five-regime developmental sweep of post-training methods for dialogue-game competence (LM Playschool Challenge 2026, team DAIR).

LoRA supervised fine-tuning of Qwen3.5-2B on success-filtered gameplay transcripts from the public playpen-data corpus (~20.2k successful per-player trajectories), mixed with ~12% general instruction data (SmolTalk) to guard against catastrophic forgetting; 22,626 conversations total, loss on assistant tokens only. Two epochs, LoRA r=32/alpha=64, lr 1e-4 cosine, effective batch 16, bf16; adapter merged.

Effect: raises clemscore 13.63 -> 55.61, almost entirely by eliminating aborted episodes (protocol compliance) rather than by improving move quality.

All numbers are clemscore / statscore on the playpen validation split, measured in a single frozen environment (Python 3.11, clemcore pinned via playpen, clembench pinned requirements) with two upstream fixes applied: a division-by-zero guard in the privateshared Game Master and the punkt_tab NLTK resource for the IFEval scorer. Earlier revisions of this card reported numbers from an unpinned environment; see the paper for the environment-sensitivity analysis.

Checkpoint family (LM Playschool challenge, team DAIR)

Regime Repo clem stat
R1 imitation (SFT) lm-playschool-qwen3.5-2b-sft 55.61 43.87
R2 outcome contrast (DPO) lm-playschool-qwen3.5-2b-sft-dpo 67.39 44.72
R3 self-imitation (SFT) lm-playschool-qwen3.5-2b-iter3 61.06 44.01
R4 corrective feedback (DPO) lm-playschool-qwen3.5-2b-iter4 67.64 44.31
R5 GRPO (control) lm-playschool-qwen3.5-2b-grpo-base-s42 62.43 44.19
R5 GRPO + RND lm-playschool-qwen3.5-2b-grpo-rnd-s42 67.44 43.53

Base model: Qwen3.5-2B (13.63 / 44.22 in the same environment). Paper: Raising a Small Language Model: From Imitation to Curiosity in Dialogue Games (LM Playschool Challenge 2026).

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