Codex App 26.715.9868.0 / CLI 0.145.0: spawn_agent rejects gpt-5.6-luna with multi_agent_v2 enabled

Start at the native spawn_agent entry point and inspect how MultiAgent V2 resolves the active model catalog and account or rollout availability. Reproduce with CLI 0.145.0, both multi-agent flags enabled, and gpt-5.6-luna with xhigh reasoning. Done means Luna is either accepted and a child agent is created, or its unavailability is exposed clearly with documented guidance.

What version of the Codex App are you using (From “About Codex” dialog)?

26.715.9868.0 (Windows package version)

What subscription do you have?

ChatGPT account; exact subscription tier is not displayed in this session.

What platform is your computer?

Microsoft Windows 11 Pro, NT 10.0.26200.0, x64 (build 26200)

What issue are you seeing?

The Codex desktop app is configured to use the standalone Codex CLI 0.145.0 through CODEX_CLI_PATH. The desktop log confirms that it spawned the external executable, and codex --version returns codex-cli 0.145.0.

Both multi-agent flags are enabled:

multi_agent     stable  true
multi_agent_v2  stable  true

After fully restarting the desktop app, an explicit native subagent request with Luna and xhigh reasoning is rejected:

{
  "fork_turns": "none",
  "model": "gpt-5.6-luna",
  "reasoning_effort": "xhigh",
  "task_name": "teste_luna_xhigh_v2"
}

Actual error:

Unknown model `gpt-5.6-luna` for spawn_agent. Available models: gpt-5.6-sol, gpt-5.6-terra

No child agent is created. The same result was reproduced after enabling MultiAgent V2 and restarting the app.

What steps can reproduce the bug?

1. Install the official Windows x64 Codex CLI release 0.145.0.
2. Point the Codex desktop app to it using CODEX_CLI_PATH=%LOCALAPPDATA%\Programs\OpenAI\Codex\bin\codex.exe.
3. Verify codex --version returns codex-cli 0.145.0.
4. Run codex features enable multi_agent_v2 and verify both multi_agent and multi_agent_v2 are true.
5. Fully quit and reopen the Codex desktop app.
6. In a desktop task, call the native spawn_agent tool with fork_turns: "none", model: "gpt-5.6-luna", and reasoning_effort: "xhigh".
7. Observe the unknown-model error stating that only gpt-5.6-sol and gpt-5.6-terra are available.

What is the expected behavior?

If Luna is intended to be available for configurable MultiAgent V2 children on this account/backend, spawn_agent should accept gpt-5.6-luna with xhigh reasoning and create the child agent.

If Luna is intentionally unavailable because of an account, rollout, backend, or entitlement restriction, the app should expose that limitation clearly and document how users can determine or obtain the required availability. Currently the local feature is stable and enabled, but the requested model remains impossible to select.

Additional information

The 0.145.0 release notes describe configurable sub-agent models/reasoning in MultiAgent V2 and mention GPT-5.6 Terra and Luna variants, which led to the expectation that Luna could be selected when using the new release.

This appears distinct from #20077 (full-history inheritance/model override behavior) and #26753 (encrypted tool schema request failure): this report reaches the spawn_agent tool and is rejected specifically because Luna is absent from the active model catalog.

The issue was reproduced multiple times. No files were modified by the failed subagent calls, and no child agent was created.