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OpenAI

Codex, the SDKs, and the engine behind ChatGPT

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The Wire · Showcase

CODEX LOCKS DOWN THREAD HISTORY, ADDS FORK PRECISION

By RepoJournal · Filed · About OpenAI

Codex shipped three structural upgrades overnight that tighten session management, prevent thread degradation across binary versions, and give you surgical control over fork boundaries.

The biggest move is immutability enforcement on thread.history_mode [1]. An older binary could append metadata that omits this field; when a newer binary replays it, serde defaults to legacy and SQLite downgrades a paginated thread. That's now locked after the canonical first SessionMeta write. Separately, the process-owned code-mode session client landed [2], a complete rewrite of session lifecycle that makes dropped calls cancellation-safe with explicit ownership handoff and validates cell/delegate state transitions end-to-end. On the API side, thread/fork now accepts an optional turnId parameter [3], letting you fork up to and including a specific turn while dropping everything after it, replacing the deprecating thread/rollback endpoint with something more granular. Finally, Codex can now consult user-level code-review skills in addition to repo-level ones [4], giving you a cleaner way to inject custom review criteria without forking configuration.

Action items

References

  1. [1] ensure thread.history_mode is immutable (#30261) openai/codex
  2. [2] [codex] add process-owned code-mode session client (#30112) openai/codex
  3. [3] feat(app-server): add optional turn_id to thread/fork (#30277) openai/codex
  4. [4] Let Codex consult user-level code-review-* skills. (#30143) openai/codex

FAQ

What changed in OpenAI on June 27, 2026?
Codex shipped three structural upgrades overnight that tighten session management, prevent thread degradation across binary versions, and give you surgical control over fork boundaries.
What should OpenAI teams do about it?
Review your thread/fork calls and test turnId parameter if you're currently using thread/rollback • Verify session handling in production after the process-owned session client upgrade deploys • Check for any custom security check wording that may conflict with updated checks
Which OpenAI repositories shipped on June 27, 2026?
openai/codex

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