OpenCode

Configure the Anthropic provider in ~/.config/opencode/opencode.jsonc on Linux/macOS or C:\Users\%USERNAME%\.config\opencode\opencode.jsonc on Windows.

{
  "$schema": "https://opencode.ai/config.json",
  "provider": {
    "anthropic": {
      "options": {
        "baseURL": "https://api.model-gate.com/v1",
        "apiKey": "mg_live_..."
      }
    }
  }
}

For OpenCode, baseURL includes /v1. Save the file and launch OpenCode normally.