Hugging Face Ships Harness Adapters: RL-Trained LoRAs Inside Unmodified pi / OpenCode / Hermes, with safeagents Blocking Reward Hacks
On 2026-11-06 Hugging Face Harness Hub released Harness Adapters: one rank-32 LoRA per base model and coding harness (pi, OpenCode, Hermes), trained with GRPO on verifiable tasks inside unmodified harnesses. Vendor smoke evals claim fewer tool calls with equal or better accuracy. A safeagents proxy rule-checks every tool call and blocks reward hacks. Bases include LiquidAI LFM2.5-24B-A2B, LFM3-1.7B, and experimental TwIL-8B.

Key Takeaways
- Mechanics: one LoRA per model x harness (rank 32, all-linear), GRPO-trained inside unmodified pi / OpenCode / Hermes
- Safety: safeagents proxy rule-checks tool calls (undeclared tools, test edits, reward-file writes, answer-source fetches); blocked rollouts score 0
- Vendor smoke: fewer tool calls than the base with equal or better accuracy; one vLLM serves named adapters
- Envs: SmolDataEnvs plus 230 Repo2RLEnvs tasks (repair/build/extend) rebuilt from public Hub trajectories
- Open: blog, safeagents, training recipe, and live dashboard; follow runs at https://harness-hub-harness-adapters-rl.hf.space/

