Meet Harness-1: A 20B Retrieval Subagent Trained With Reinforcement Learning Inside a Stateful Search Harness on gpt-oss-20b
Harness-1 is a 20B retrieval subagent that separates search decisions from bookkeeping by using a stateful harness. It achieves 0.730 average curated recall across eight benchmarks, outperforming other open models and nearing frontier performance. The model is trained with supervised fine-tuning for interface operation and reinforcement learning for search policy, using a finite set of tools and a working memory. Weights and harness code are publicly released on Hugging Face and GitHub.