Senior SWE-Bench We treat agents like senior engineers, so why evaluate them like junior engineers? Senior engineers build features without over-specified requirements Senior SWE-Bench feature tasks have realistic instructions that read like natural language messages rather than over-specified requirements. To reliably evaluate these tasks, we introduce a validation agent which uses expert-designed recipes to write behavioral tests that adapt to submitted solutions. Senior engineers solve bugs that require runtime investigation from behavioral reports Senior SWE-Bench bug tasks reflect tricky