Microsoft’s SkillOpt Shows Optimized Agent Skill Artifacts Transfer Across Model Scales and Between Codex and Claude Code Harnesses

Most coverage of Microsoft's SkillOpt centers on its 52/52 result. The more consequential finding is in Section 4. 3: the exported best_skill. md keeps working in environments it was never trained on. A Codex-trained SpreadsheetBench skill lifted Claude Code from 22. 1 to 81.

8, slightly above the 80. 4 that harness reached training its own skill. Retention varies sharply by task type — 102% on spreadsheets, 10% on math — which is what makes the result worth reading closely.