feat: allow custom models for Anthropic provider with custom base URLs

[roomote]

Summary

This PR addresses Issue #8488 by enabling custom model IDs when using the Anthropic API provider with custom base URLs. This enhancement allows users to leverage services like z.ai that provide Anthropic-compatible endpoints with their own custom models (e.g., glm-4.6-cc-max, glm-4.5v).

Changes

Backend (src/api/providers/anthropic.ts)

• Modified getModel() method to detect when a custom base URL is configured
• When using a custom base URL, any model ID is now accepted (not just predefined Claude models)
• Provides sensible defaults for unknown models (200k context window, conservative feature flags)
• Maintains backward compatibility - predefined models still work with their specific configurations

Frontend (webview-ui/src/components/settings/providers/Anthropic.tsx)

• Added ModelPicker component that appears when custom base URL is enabled
• Users can now select from predefined models or enter any custom model ID
• Added helpful text explaining the custom model capability

UI Flow (webview-ui/src/components/settings/ApiOptions.tsx)

• Prevents duplicate model selectors when Anthropic provider uses custom base URL

Testing

• Added comprehensive test suite in src/api/providers/__tests__/anthropic.custom-models.spec.ts
• Tests cover standard models, custom models, auth token handling, and API calls
• All existing tests continue to pass

Use Case

Users of services like z.ai can now:

1. Select Anthropic as their API provider
2. Enable custom base URL and enter their service endpoint (e.g., https://api.z.ai/api/anthropic)
3. Enter any custom model ID their service supports (e.g., glm-4.6-cc-max)
4. Use these custom models with full Roo Code functionality

Testing Instructions

1. Go to Settings → API Provider → Select "Anthropic"
2. Enter your API key
3. Check "Use custom base URL"
4. Enter a custom URL (e.g., https://api.z.ai/api/anthropic)
5. Notice the model picker now appears
6. Type a custom model name (e.g., glm-4.6-cc-max)
7. Select "Use custom model: glm-4.6-cc-max" from the dropdown
8. The custom model should now be usable

Backward Compatibility

• ✅ Existing Anthropic configurations continue to work unchanged
• ✅ Standard Claude models work with or without custom base URLs
• ✅ No breaking changes to the API

Fixes #8488

---

Important

Adds support for custom model IDs and base URLs for the Anthropic provider, with frontend and backend changes ensuring backward compatibility.

• Backend (src/api/providers/anthropic.ts):
  • getModel() now supports custom model IDs with custom base URLs, providing default settings for unknown models.
  • Maintains predefined model configurations for known models, even with custom base URLs.
• Frontend (webview-ui/src/components/settings/providers/Anthropic.tsx):
  • Introduces ModelPicker for custom model selection when a custom base URL is set.
  • Adds explanatory text for custom model capabilities.
• UI Flow (webview-ui/src/components/settings/ApiOptions.tsx):
  • Prevents duplicate model selectors for Anthropic with custom base URLs.
• Testing:
  • New tests in src/api/providers/__tests__/anthropic.custom-models.spec.ts for custom model handling, including API calls and token counting.
• Backward Compatibility:
  • Existing Anthropic configurations and standard models remain functional without changes.

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[roomote]

Self-review: audited my own diff and found a race condition between me and myself.

[roomote]

P3 – Hardcoded UI string bypasses i18n. Consider adding an i18n key (e.g., settings:providers.anthropicCustomModelHelp) and using t(...) to stay consistent with the rest of the settings UI.

[daniel-lxs]

#8488 (comment)

[cobra91]

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