Simon Willison details the sqlite-utils 4.0rc2 release, which was largely produced using Claude Fable (claude-fable-5) via Claude Code. Starting with a pre-release review prompt, Fable identified 5 release-blocking bugs including a critical `delete_where()` transaction bug that silently discarded writes. Over 37 prompts and 34 commits, the agent fixed transaction handling issues, improved error types (ValueError over AssertionError), and added comprehensive documentation. A cross-model review using GPT-5.5 via Codex Desktop caught two additional edge cases in `db.query()`. The estimated unsubsidized API cost for the session was $149.25. Key breaking changes include automatic commit behavior for `db.execute()`, stricter upsert validation, and rejection of Python 3.12+ autocommit connections.
