Ant's PAR trains a 0.5B model to extrapolate state tracking 16x beyond training length

ant-intl · hf · 2026-10-21

Ant International and NUS propose Progress-Aligned Recurrence (PAR), which aligns the prediction at iteration k with the state after the first k operations and rescales recurrent states to first-iteration norms, fixing scale drift under final-answer supervision. On swap-S5, a Qwen2.5-0.5B trained on at most 32 moves hits 95.5% mean full-state accuracy at 512 moves (16x training length) vs 55.7% for RLT and 0.8% for explicit chain-of-thought on the same backbone. Ablations show norm anchoring is essential (extrapolation drops below 2x without it); a learned completion redundancy mechanism handles stopping, and prefix self-distillation works without intermediate labels.

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