Every datetime the API emits for versions (flow summaries' updated_at, runs' created/started/finished with flow_version) is already ISO 8601 with Z or +00:00. A test holds it and the API docs say so. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01WgBfkm4rCmtd1T4vHWjEPx