lm-playschool-qwen3.5-2b-iter3

R3 — Self-imitation (SFT)

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

One light SFT epoch on the model's own successful episodes: the R2 model played the full public instance sets of eight games (490 episodes, 63% successful; validation-overlapping instances excluded), yielding 516 per-player trajectories. LoRA r=16, lr 2e-5, no KL anchor, no general-data replay.

Effect: a regression, 67.39 -> 61.06. Rehearsing one's own successes, delivered through an unanchored objective, perturbed behaviour on games both present in and absent from the self-play data. Released as a negative result; we rule out a train/inference format mismatch and reversion toward the pre-DPO policy (see paper).

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)

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). <!-- TODO: add link -->