Do AI coding agents care about SemVer or is it something for humans only?

Microsoft ran two Vally experiments with GitHub Copilot CLI (nearly 1,000 runs) and found that some models, notably Claude Sonnet 5.5 and Claude Haiku 5.5, checked upgrades less often when the version label was a patch than when it was a major release, even with byte-identical code. Three models (Claude Opus 5.5, GPT-6.1 Sol, GPT-6.1 Terra) checked every update regardless of label, and all four merges that left main broken came with a patch or minor label. The author recommends keeping SemVer honest, enforcing CI on every dependency branch, and treating the version number as a hidden variable when evaluating agents.