feat: add Azure Anthropic (Claude) provider support

[nogataka]

Summary

• Add Azure Anthropic (Claude) as a first-class API provider, enabling users to route Claude API calls through Azure AI Services endpoints instead of Anthropic's direct API
• Fix Settings UI to properly support providers that require user-supplied Base URLs

Background

Azure AI Services hosts Claude models at custom endpoints (https://{resource}.services.ai.azure.com/anthropic). Unlike other alternative providers (GLM, Ollama, Kimi) which have fixed base URLs, each Azure customer has a unique resource-specific endpoint.

A key discovery during implementation: the Claude Code CLI ignores ANTHROPIC_BASE_URL when ANTHROPIC_AUTH_TOKEN is set, as it falls back to its own subscription authentication. The fix is to use ANTHROPIC_API_KEY instead, which forces the CLI into API key authentication mode and properly respects the custom base URL.

Changes

Backend

registry.py

• Add "azure" entry to API_PROVIDERS with auth_env_var: "ANTHROPIC_API_KEY" (critical for correct routing), empty base_url (user must provide their own), and Claude model options (Opus, Sonnet, Haiku)

client.py

• Add Azure endpoint detection (services.ai.azure.com in base URL) with proper "Azure Mode" log label
• Rename misleading "GLM Mode" fallback label to "Alternative API"

Frontend

ui/src/components/SettingsModal.tsx

• Show Base URL input field when Azure provider is selected (previously only shown for "Custom")
• Add Azure-specific placeholder text (https://your-resource.services.ai.azure.com/anthropic)
• Add "Configured" state with green checkmark and "Change" button for saved Base URLs (matching existing API Key UX pattern)
• Widen Settings modal from max-w-sm (384px) to max-w-lg (512px) for better readability with longer URLs

Configuration

.env.example

• Add Azure Anthropic env var template with ANTHROPIC_API_KEY (not ANTHROPIC_AUTH_TOKEN)
• Update section header to include Azure in the provider list

Key Technical Details

Why ANTHROPIC_API_KEY instead of ANTHROPIC_AUTH_TOKEN?

Testing revealed that the Claude Code CLI behaves differently depending on the auth env var:

Env Var	CLI Behavior
ANTHROPIC_AUTH_TOKEN	CLI uses its own subscription auth, ignores ANTHROPIC_BASE_URL
ANTHROPIC_API_KEY	CLI uses API key auth, respects ANTHROPIC_BASE_URL

This means Azure (and any custom endpoint) must use ANTHROPIC_API_KEY to ensure requests are routed to the correct endpoint.

How to Use

Via Settings UI (recommended)

1. Open Settings (gear icon or , key)
2. Select "Azure Anthropic (Claude)" from the provider dropdown
3. Enter your Azure endpoint URL (e.g., https://myresource.services.ai.azure.com/anthropic)
4. Enter your Azure API key
5. Select a model

Via .env file

ANTHROPIC_BASE_URL=https://your-resource.services.ai.azure.com/anthropic
ANTHROPIC_API_KEY=your-azure-api-key
ANTHROPIC_DEFAULT_OPUS_MODEL=claude-opus-4-6
ANTHROPIC_DEFAULT_SONNET_MODEL=claude-sonnet-4-5
ANTHROPIC_DEFAULT_HAIKU_MODEL=claude-haiku-4-5

[leonvanzyl]

Thanks