Missing newer models (Opus 4.6, GPT 5.3) when using `@github/copilot-language-server` via ACP

[magicxor]

Hello,

I am currently integrating the GitHub Copilot Agent Client Protocol (ACP) within JetBrains Rider. I have noticed a discrepancy in the available models depending on how the language server is launched.

The Issue
When I run the agent using the npm package @github/copilot-language-server@1.430.0, the newer models (specifically GPT 5.3 and Opus 4.6) are not listed in the available models list.

Configuration (NPM Package - Missing Models)
Here is the configuration where the models are missing:

{
    "agents": {
        "acp.registry.github-copilot": {
            "agent": {
                "id": "github-copilot",
                "name": "GitHub Copilot",
                "version": "1.430.0",
                "description": "GitHub's AI pair programmer",
                "repository": "https://github.com/github/copilot-language-server-release",
                "authors": [
                    "Microsoft"
                ],
                "license": "proprietary",
                "icon": "https://cdn.agentclientprotocol.com/registry/v1/latest/github-copilot.svg",
                "distribution": {
                    "binary": null,
                    "npx": {
                        "package": "@github/copilot-language-server@1.430.0",
                        "args": [
                            "--acp"
                        ],
                        "env": {}
                    },
                    "uvx": null
                }
            },
            "installedAt": 1771225162562,
            "lastUsedAt": 1771225162562
        }
    }
}

Comparison (CLI Executable - Working Correctly)
However, when I configure the agent using the copilot.exe console application, these models are present and work as expected.

CLI Configuration:

{
  "default_mcp_settings": {},
  "agent_servers": {
    "Copilot Local CLI App": {
      "command": "copilot",
      "args": [
        "--acp"
      ]
    }
  }
}

Environment Details:

• IDE: JetBrains Rider 2025.3.2 Build #RD-253.30387.148, built on January 29, 2026
• Package: @github/copilot-language-server@1.430.0
• Protocol: Agent Client Protocol (ACP)

Could you please clarify if the NPM package version requires a specific flag to expose these newer models, or if the 1.430.0 release has not yet been updated to include the definitions for GPT 5.3 and Opus 4.6 compared to the binary release?

Thank you for your help.