feat: add GPT-5 Codex model support

[Patrick-Erichsen]

Blocked by #7891
Resolves CON-4119

Note that this model will be included automatically in the handful of places we do model specific checks for tools, etc, because we are either checking for gpt for gpt-5, and this model is named gpt-5-codex

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Summary by cubic

Added GPT-5 Codex support so it can be selected under OpenAI. Enables chat and edit workflows with up to 500k context and 150k max completion tokens.

• New Features
  • Added GPT-5 Codex to the Add New Model UI and OpenAI provider list.
  • Registered model in llm-info with id gpt-5-codex, display name, 500k context, 150k max tokens, regex, and recommendedFor ["chat", "edit"].
  • Automatically covered by existing gpt/gpt-5 tool-use checks.

[github-actions]

✅ Review Complete

Code Review for PR #8350: feat: add GPT-5 Codex model support

Overall Assessment

The changes look solid and follow existing patterns correctly. The implementation is straightforward and properly integrates the new model into all necessary locations.

✅ Positives

• Consistent with existing model definitions across all three files
• Proper placement in the OpenAI provider packages list (maintained alphabetical ordering with other GPT-5 models)
• Correct metadata: context length (500k), max completion tokens (150k), and recommended use cases

🔍 Issues Found

1. Missing model in core provider list (Medium Priority)

• Location: packages/llm-info/src/providers/openai.ts
• Issue: The new model is added to the modelInfo array but should also be checked against the main models array in the same file if one exists. Need to verify the model is properly exported and available for use.
• Suggestion: Ensure the model is included in any exports or model lists that downstream code relies on.

2. Tool support verification needed (Low Priority)

• Location: General concern
• Issue: The PR description mentions "automatically covered by existing gpt/gpt-5 tool-use checks" but we should verify:
  • Does gpt-5-codex match the /gpt-5/ regex in openai.ts line 84? No, it doesn't - the regex /gpt-5/ will match "gpt-5-codex" but the more specific model definition should take precedence.
  • Are there any other places checking for model names with more specific patterns like startsWith('gpt-5') that might not include the codex variant?
• Suggestion: Search for tool support checks to confirm they work with the hyphenated model name:

  grep -r "gpt-5" --include="*.ts" core/

3. Consider adding to autocomplete models (Question)

• Location: May be elsewhere in the codebase
• Issue: Since this is a code-focused model, should it also be marked as suitable for autocomplete?
• Suggestion: Check if autocomplete models are configured elsewhere and whether GPT-5 Codex should be included.

Minor Observations

• The underscores in contextLength: 500_000 are good for readability (line 1088)
• Icon and provider settings are correctly configured

Recommended Actions Before Merge

1. ✅ Verify the regex patterns in tool support code actually match "gpt-5-codex"
2. ✅ Confirm the model is properly exported from llm-info package
3. ⚠️ Consider if autocomplete support should be added

The code quality is good and follows established patterns. Main concern is ensuring downstream tool-use detection works as claimed in the PR description.

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[cubic-dev-ai]

No issues found across 3 files