Decision models target structured tasks by directly predicting choices or scores, avoiding autoregressive decoding latency.
However, transferring a generative LLM's ranking knowledge to a decision model remains challenging: the teacher expresses preferences through a ranked list of document ID sequences, while the student determines the ranking using scores from the first-token position.
Proposed Method: DecisionRank
To bridge this gap, we introduce DecisionRank, a decision model trained through item-space on-policy distillation (OPD). Item-space OPD constructs the student's rollout by sorting its document scores into a ranked sequence. A generative teacher takes the resulting ranking list as inputs and provides conditional feedback to directly supervise those scores.
Performance Highlights
- Combined with offline ranking supervision, DecisionRank achieves state-of-the-art performance on both general and reasoning-intensive retrieval benchmarks such as TREC DL, BEIR, and BRIGHT.
- Across four benchmarks, item-space OPD consistently outperforms alternative training objectives.
- Even at 1.7B parameters, DecisionRank surpasses its 27B generative teacher on TREC DL19--23.
- At 8B, it outperforms its generative listwise counterpart while running $24.5\times$ faster on TREC DL and $16.7\times$ faster on BRIGHT.