Codex changed its default model in a hotfix and removed mcp-server in a minor
In rust-v0.153.4 (2026-09-04) the bundled catalog's gpt-6-astra entry, already priority 1 but hidden, became visible (PR 42874), and the picker default moved from gpt-5.6-sol to gpt-6-astra for sessions with no model set. rust-v0.154.0 removed the deprecated codex mcp-server entry point (PR 42993). Guardian V2 stayed default-off in every stable read, nine of the window's fourteen, and 0.153.0 stopped Guardian review in Full Access and User approval modes. npm latest at close was 0.155.1.
What this changes for operators
- Pin model explicitly if cost, latency or eval baselines matter; a patch upgrade changed it. Grep configs for gpt-5.5 before its 2026-10-14 retirement from ChatGPT sign-in.
- Integrations built on codex mcp-server break at 0.154.0; the app server is the path.
- Do not plan as if a model reviews every call: Guardian V2 is off, and Guardian itself no longer runs in two modes.
Primary sources
- github_release 2026-09-21-codex-default-model-moved-to-gpt-6-astra-in-the-0-153-x-hotfix-train-not-in-a-minor openai/codex / rust-v0.153.4
- tagged_commit_file 2026-09-21-codex-default-model-moved-to-gpt-6-astra-in-the-0-153-x-hotfix-train-not-in-a-minor openai/codex / codex-rs/models-manager/models.json
- github_release 2026-09-21-codex-codex-mcp-server-removed-app-server-is-the-only-integration-path-and-it-is-officially-expe openai/codex / rust-v0.154.0
- merged_pr 2026-09-21-codex-codex-mcp-server-removed-app-server-is-the-only-integration-path-and-it-is-officially-expe github.com/openai/codex/pull/42993
- official_docs 2026-09-21-codex-codex-mcp-server-removed-app-server-is-the-only-integration-path-and-it-is-officially-expe learn.chatgpt.com/docs/changelog
- tagged_commit_file 2026-09-21-codex-guardian-v2-stayed-off-by-default-in-every-stable-of-the-window-carry-forward openai/codex / codex-rs/features/src/lib.rs#L1593-L1596
- tagged_commit_file 2026-09-21-codex-guardian-v2-stayed-off-by-default-in-every-stable-of-the-window-carry-forward openai/codex / codex-rs/features/src/lib.rs#L1563-L1566
- github_release 2026-09-21-codex-guardian-no-longer-runs-in-full-access-or-user-approval-mode openai/codex / rust-v0.153.0
Signal metadata
Source findings
- 2026-09-21-codex-default-model-moved-to-gpt-6-astra-in-the-0-153-x-hotfix-train-not-in-a-minor 2026-09-21-codex-default-model-moved-to-gpt-6-astra-in-the-0-153-x-hotfix-train-not-in-a-minor
- 2026-09-21-codex-codex-mcp-server-removed-app-server-is-the-only-integration-path-and-it-is-officially-expe 2026-09-21-codex-codex-mcp-server-removed-app-server-is-the-only-integration-path-and-it-is-officially-expe
- 2026-09-21-codex-guardian-v2-stayed-off-by-default-in-every-stable-of-the-window-carry-forward 2026-09-21-codex-guardian-v2-stayed-off-by-default-in-every-stable-of-the-window-carry-forward
- 2026-09-21-codex-guardian-no-longer-runs-in-full-access-or-user-approval-mode 2026-09-21-codex-guardian-no-longer-runs-in-full-access-or-user-approval-mode
Featured in
- Before the First Turn / 2026-09-21
Run: 2026-09-21-weekly-digest-2026-08-20_2026-09-21-frontier-v0
Schema: bitter.frontier_signals.v0 / ID: 2026-09-21-codex-default-model-moved-in-a-hotfix
Research evidence and publication history are open in the repository.