Google’s RRSI framework lets AI agents rebuild their own harnesses

Google Cloud AI Research has released RRSI, an open-source framework that lets AI agents keep rewriting the machinery around their own language model. The model itself stays fixed. Everything bolted onto it is fair game. What RRSI actually does RRSI stands for Regularized Recursive Self-Improvement of Agent Harnesses. It was introduced on September 21, 2026, in collaboration with UNC-Chapel Hill, Stanford, and Washington University in St. Louis. The code is available under the Apache 2.0 license, which is permissive enough for commercial use. A quick primer on the word “harness.” If the language model is an engine, the harness is the rest of the car: steering, transmission, dashboard, glovebox. Technically, it covers the prompts, control flow, tools, and memory management that turn a raw model into an agent capable of completing tasks. RRSI lets the agent propose edits to that harness, test them, and keep the ones that work. Then it repeats the loop. The “recursive” part means the improved harness becomes the starting point for the next round of improvements. The “regularized” part of the name addresses the overfitting problem. The framework opens the full edit space, then constrai...