OpenAI Day 19 ships Codex CLI 0.164.0, keeps cache across reasoning switch

Day 19 follows a pattern in OpenAI's 28-day update run where some days announce usage resets and others focus on product improvements. This one falls in the latter category, and the body explicitly notes no new full reset was announced. The Codex CLI 0.164.0 release itself landed on GitHub at 04:48 UTC on October 23, ahead of the Day 19 announcement around 08:12 Japan time on October 24, a timing gap.

The cache change is a follow-on to Day 16's work on reusing cache for older conversations after time away. Day 19 targets a different failure mode: switching reasoning level inside an ongoing conversation. The change removes only the reasoning-level trigger for cache invalidation, not other causes, and does not guarantee a percentage reduction in usage or cost.

Alongside the CLI features, the release carries enterprise-oriented fixes — MCP authentication options, masking of credentials in remote execution paths, Windows proxy authentication via Negotiate/NTLM, and macOS sandbox checks around case-variant metadata paths and replaceable symlinks. Tibo Sottiaux also reported that Codex CLI usage roughly doubled since DevDay, though the metric behind that figure is not specified and does not mean speed or quota doubled.