Harness adapters: Safe RL for efficient agentic development

Hugging Face's harness-hub team released LoRA "harness adapters" for LFM2.5-24B-A2B, LFM3-1.7B and TwIL-8B, trained with GRPO inside unmodified pi, opencode and hermes harnesses. One vLLM server hosts all adapters, and a rule-based proxy, safeagents, blocks reward-hacking tool calls and scores them 0. The authors report fewer tool calls at equal or better held-out accuracy, but only from smoke tests, and most figures lack independent sourcing. The new task set is 94% build tasks.