feat: add GitHub Copilot GPT-5.3 Codex

[anjulgarg]

Summary

• add GitHub Copilot gpt-5.3-codex model config
• include capabilities, limits, and modalities aligned with 5.3 Codex
• set Copilot pricing to zero

[rekram1-node]

Not available to oc users yet.

[anjulgarg]

@rekram1-node Curious, what needs to happen to make it available in oc?
I am able to use this model in vscode using gh copilot

[rekram1-node]

The model isn't fully rolled out yet. So once it is it can be used in other clients.

[cfryerdev]

This model is available in Github Copilot as of this week, but under preview, do we not merge preview models so they become available in OpenCode?

I would like to roll this out to the teams that use opencode over copilot-vscode

[rekram1-node]

Not sure I'm following?

[anjulgarg]

Hi @rekram1-node I don't understand what you mean by "fully rolled out",
If the models is showing up in vscode through github copilot, oc can use it too.
If you mean that its not rolled out globally to everyone, even in that case, isn't it better to add it so that those who have access to it can use it instead of blocking it for everyone?

[cfryerdev]

This model is available in GA. Please merge

[rekram1-node]

If the models is showing up in vscode through github copilot, oc can use it too.

This is not the case actually, oc uses it's own oauth id, github copilot filters models based on their id vs id belonging to other clients. Last I checked this was still not enabled for other clients.

I also talked w/ their team yesterday and they said rollout has been slow due to incidents it is not generally available for all copilot clients yet.

[anjulgarg]

@rekram1-node that's a really good detail. I wan unaware of it. That explains why now selecting and using 5.3 codex in OC shows an error about the model not being supported. My bad :/
Hopefully, they rollout to OC soon.
I can revert this PR if that's a better experience.

[rekram1-node]

You can test models without them being in models.dev:

{
  "$schema": "https://opencode.ai/config.json",
  "provider": {
    "github-copilot": {
      "models": {
        "gpt-5.3-codex": {},
      },
    },
  },
}

[cfryerdev]

Very much appreciate the clarification, @rekram1-node