gpt-5.6-luna still returns Model not found on v1.17.19 while codex-cli 0.144.1 works

[Lou-peng]

Description

This still reproduces on OpenCode v1.17.19. Please reopen.

Environment:

• OpenCode: 1.17.19
• Authentication: ChatGPT OAuth
• Provider: built-in OpenAI provider
• Model: openai/gpt-5.6-luna
• No custom baseURL or OPENAI_API_KEY

OpenCode result:
Model not found gpt-5.6-luna

Control test with the same ChatGPT account:

• codex-cli: 0.144.1
• codex exec --ephemeral -m gpt-5.6-luna "Reply with exactly: ok"
• Result: success (ok)

This rules out account/plan gating and suggests that OpenCode's Responses
Lite request contract still differs from the official Codex CLI, possibly
the originator: opencode versus originator: codex_cli_rs behavior.

Plugins

No response

OpenCode version

No response

Steps to reproduce

No response

Screenshot and/or share link

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Operating System

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Terminal

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[github-actions]

This issue might be a duplicate of existing issues. Please check:

• GPT-5.6 Luna returns model not found with ChatGPT OAuth #36140: GPT-5.6 Luna returns model not found with ChatGPT OAuth (same symptom, same codex-cli comparison, same OAuth path — now closed)
• Auth error with GPT 5.6-xxx models #36133: Auth error with GPT 5.6-xxx models (broader report covering the same family)
• GitHub Copilot 5.6 models (gpt-5.6-luna/sol/terra) return 403 Forbidden #36575: GitHub Copilot 5.6 models (gpt-5.6-luna/sol/terra) return 403 Forbidden (related 5.6 family failures)

Issue #36140 in particular covers the same root cause: OpenCode's Responses request path differs from the Codex CLI transport contract for the Luna model with ChatGPT OAuth.

[jasoncarreira]

I independently reproduced this with the built-in OpenAI ChatGPT OAuth provider on OpenCode 1.17.15 after removing the third-party opencode-openai-codex-auth plugin. Sol and Terra work; Luna enters the retry loop with Model not found gpt-5.6-luna.

The remaining identity mismatch is visible in the 1.17.19 source:

• CODEX_COMPATIBILITY_VERSION is now 0.144.0, and the Responses Lite adapter sends it as the version header.
• chat.headers still sends originator: opencode.
• User-Agent is still opencode/<OpenCode version> (...).
• The rewritten Codex endpoint has no client_version query parameter.

Source references:

• CODEX_COMPATIBILITY_VERSION
• request URL rewrite
• originator and User-Agent
• version header

This is consistent with the controlled matrix in openai/codex#31967: Luna succeeds only when the backend recognizes both the Codex client identity and a new-enough version. A separate implementation that works against this gate presents:

originator: codex_cli_rs
User-Agent: codex_cli_rs/0.144.1
.../codex/responses?client_version=0.144.1

I understand the concern raised on #36314 that OpenCode should not impersonate Codex. If OpenAI does not support third-party originators for Luna, then the durable resolution likely requires OpenAI to register/allow the opencode identity. In the meantime, OpenCode 1.17.19 advertises Luna but cannot use it for affected OAuth accounts, so hiding it or returning a bounded actionable error would be preferable to the current unbounded retry.

[Lou-peng]

This is not just a duplicate of #36140; it is a regression/fix verification
against the release that was supposed to resolve #36140.

#36140 was closed by PR #36685, and that fix is included in OpenCode v1.17.19.
However, the issue still reproduces on the stable v1.17.19 release:

• OpenCode 1.17.19
• Built-in OpenAI provider
• ChatGPT OAuth
• openai/gpt-5.6-luna returns:
  Model not found gpt-5.6-luna
• No custom baseURL or OPENAI_API_KEY
• The same ChatGPT account succeeds with:
  codex-cli 0.144.1
codex exec --ephemeral -m gpt-5.6-luna "Reply with exactly: ok"

The other suggested issues are different:

• Auth error with GPT 5.6-xxx models #36133 uses a custom proxy/API-key path.
• GitHub Copilot 5.6 models (gpt-5.6-luna/sol/terra) return 403 Forbidden #36575 concerns GitHub Copilot and returns HTTP 403.
• This report concerns the built-in OpenAI ChatGPT OAuth path and HTTP
  404 after the fix(opencode): support Luna Responses Lite over OAuth #36685 fix was released.

Please either reopen #36140 or keep this issue open as a v1.17.19 regression.
The Codex CLI control test indicates this is not account/model-access gating.
A likely remaining difference is OpenCode using originator: opencode, while
the official Codex CLI uses originator: codex_cli_rs.