Google Research open-sources Harness², which rewrites an agent's prompts, tools, and skills per task
Harness² keeps model weights fixed and instead proposes edits to eight harness parts (system prompt, guardrails, memory, tool guidance, subagents, skills, scripts, plugins), probes them on the same task, and keeps what the run evidence supports, then saves those lessons for later tasks; it runs on OpenCode or Codex (--substrate cx) under Apache 2.0. One step lifted GLM-5 and Gemini 3.5 Flash by up to 11.5 points on WorkBuddy-Bench, per the paper, though Google says it isn't an officially supported product.