FRONTIERSWE V2

Summary from the TLDR Dev newsletter

FrontierSWE v2 expands its ultra-long-horizon engineering benchmark to 34 tasks and gives agents up to 20 hours with a harness designed to encourage longer, recoverable work. Claude Fable 5.1 leads at 56.29 percent, followed by GPT-5.6 at 32.2 percent and GLM-5.3 at 30.2 percent, while the revised methodology adds deterministic performance metrics, stronger anti-cheating isolation, and self-check feedback.