feat: add provider-scoped environment overrides (#5807)

packages/ai/README.md

@@ -38,6 +38,7 @@ Unified LLM API with automatic model discovery, provider configuration, token an
 - [Browser Usage](#browser-usage)
   - [Browser Compatibility Notes](#browser-compatibility-notes)
   - [Environment Variables](#environment-variables-nodejs-only)
+  - [Provider-Scoped Environment Overrides](#provider-scoped-environment-overrides)
   - [Checking Environment Variables](#checking-environment-variables)
 - [OAuth Providers](#oauth-providers)
   - [Vertex AI](#vertex-ai)
@@ -1145,6 +1146,24 @@ const response = await complete(model, context, {
 });
 ```
 
+### Provider-Scoped Environment Overrides
+
+Pass `env` in stream options to scope provider configuration to a request. Values in `env` are used before process environment variables for API key discovery and provider configuration such as Cloudflare account IDs, Azure OpenAI settings, Vertex project/location, Bedrock settings, `PI_CACHE_RETENTION`, and `HTTP_PROXY`/`HTTPS_PROXY`.
+
+```typescript
+const model = getModel('cloudflare-ai-gateway', 'workers-ai/@cf/moonshotai/kimi-k2.6');
+
+const response = await complete(model, context, {
+  env: {
+    CLOUDFLARE_API_KEY: '...',
+    CLOUDFLARE_ACCOUNT_ID: 'account-id',
+    CLOUDFLARE_GATEWAY_ID: 'gateway-id'
+  }
+});
+```
+
+Use this when one process needs different provider settings per request, or when ambient environment variables should not leak into a provider call.
+
 ### Checking Environment Variables
 
 ```typescript