HARTS reuses shared prefixes across agentic RL rollout trees and reports 4.77x to 10.45x the update throughput of trajectory-expanded training on SWE-bench
AspireAI community · arXiv
Agentic reinforcement learning generates irregular rollout trees, so trajectory-by-trajectory training keeps recomputing shared interaction histories. HARTS (Hybrid-Attention RL over Tree Structures) builds compression-oriented microbatches, accumulates gradients from dependent microbatches before a single backward pass through the shared prefix, and uses a linear-time planner to minimise sequential linear-attention calls. The authors report 4.77x to 10.45x update throughput over trajectory-expanded training across two sampling schemes on 7.9B- and 124B-parameter hybrid-attention mixture-of-experts models using 8 to 64 GPUs. The paper was first posted in August 2026 and revised on October 26, 2026; the speedups are measured on SWE-bench and were not independently reproduced.
Read the story and explore more from the AspireAI community.
Two sparse-autoencoder analyses have resisted scaling: matching semantically similar features across layers, and compressing large feature circuits into interpretable supernodes. This paper argues both are the same underlying problem, estimating semantic distances between SAE features that sit on different activation manifolds. Its representation treats each feature not as a single decoder vector but as an activation-weighted distribution over the hidden states expressing it, projects those distributions into a shared reference space, and compares them with Wasserstein distance. The representation is proved invariant to activation rescaling and stable under perturbation, and recovers true matches under finite-sample margin conditions. Empirically it outperformed decoder-vector and LLM-based baselines and captured subtle functional distinctions between related features, and it compressed large feature circuits into interpretable supernodes automatically. The limitation is that this is interpretability tooling: the paper demonstrates better feature matching and circuit compression, not that downstream interpretability claims become more accurate.