[FEATURE]: Support for GitHub Copilot model GPT-5.3 Codex

[RonaldProCo]

Feature hasn't been suggested before.

• I have verified this feature I'm about to request hasn't been suggested before.

Describe the enhancement you want to request

I would like to request the integration of the GPT-5.3 Codex model into OpenCode. Although OpenAI has recently moved this model to General Availability and it is already accessible via the GitHub Copilot API in other clients (like VS Code , GH Copilot CLI ), OpenCode currently limits the selection to version 5.2 Codex.

What are the benefits of implementing this?

• Superior Logic: GPT-5.3 Codex offers a significant improvement in multi-file context handling and complex architectural reasoning compared to 5.2.
• Reduced Latency: The new iteration includes optimizations for streaming responses that would benefit the OpenCode TUI/CLI experience.
• Parity with official tools: Users expect OpenCode to support the same cutting-edge models available in official GitHub extensions.

[github-actions]

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

• [FEATURE]: 5.3 Codex for Github Copilot provider #12954: [FEATURE]: 5.3 Codex for Github Copilot provider — same feature request for Codex 5.3 support
• Codex 5.3 not working with copilot #13312: Codex 5.3 not working with copilot — related issue about Codex 5.3 with the Copilot provider

Please review those issues and consider continuing the discussion there if they cover the same request.