Agent Lightning v1.0 trained an agent with the same harness it deploys, and lifted Qwen3.5-9B from 41.8% to 56.4% on SWE-bench Verified
AspireAI community · Microsoft Research
Microsoft Research Asia rebuilt Agent Lightning around what it calls Harnessed Agentic RL: the agent harness used in deployment participates directly in reinforcement learning, so the agent being trained is the agent that ships, instead of a reimplementation of it inside the training framework. The control plane is roughly 3,500 lines of code, agents run as ordinary Kubernetes jobs on self-managed, cloud or local infrastructure with no dependency on paid commercial sandbox services, and an end-to-end coding-agent pipeline raised Qwen3.5-9B from 41.8% to 56.4% Pass@1 on SWE-bench Verified - a 14.6 point gain - using about 6,000 training samples from an open dataset. The framework is open-sourced. The caveat is that 56.4% is the authors' own recipe on their own pipeline, and the post dates from October 7.
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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.