Senior SWE-Bench: open-source benchmark that assesses agents as senior engineers

Senior SWE-Bench is a new open-source benchmark that evaluates AI agents on realistic senior-level software engineering tasks rather than over-specified junior-level problems. The benchmark includes feature tasks with natural language requirements, bug tasks requiring runtime investigation, and scoring that measures code quality beyond correctness, including adherence to unstated codebase practices. It introduces a validation agent that uses expert-designed tests to assess solutions adaptively.