Simular's Agent S4 lifts an open 27B model to 21.3% on OSWorld V2
Agent S4 does not do tasks itself: it rewrites the tools a computer-use agent works through, such as a direct shell instead of typing into a terminal from screenshots, and keeps the best versions through repeated rounds of selection. With those evolved tools, Qwen3.8-27B reached 21.3% on the 108-task OSWorld V2 benchmark, 3.8 times the same model with fixed tools and above GPT-5.5 at about 4.3% of its cost. The code is open source.