fix: use OpenAI-compatible format for all Copilot models and add required headers

Switch from @ai-sdk/anthropic to @ai-sdk/openai-compatible for all models
since the Copilot API only supports OpenAI chat completions format. Add
required Copilot headers (Editor-Plugin-Version, User-Agent, openai-intent,
x-github-api-version) and update default model to claude-sonnet-4.6.

Author: maros7

src/agent/infra/llm/providers/github-copilot.ts

@@ -1,4 +1,3 @@
-import {createAnthropic} from '@ai-sdk/anthropic'
 import {createOpenAICompatible} from '@ai-sdk/openai-compatible'
 
 import type {GeneratorFactoryConfig, ProviderModule} from './types.js'
@@ -21,31 +20,19 @@ export const githubCopilotProvider: ProviderModule = {
       ...COPILOT_REQUEST_HEADERS,
     }
 
-    if (isCopilotClaudeModel(config.model)) {
-      const provider = createAnthropic({
-        apiKey,
-        baseURL: `${baseUrl}/v1`,
-        headers,
-      })
-
-      return new AiSdkContentGenerator({
-        charsPerToken: 3.5,
-        model: provider(config.model),
-      })
-    }
-
     const provider = createOpenAICompatible({
       apiKey,
-      baseURL: `${baseUrl}/v1`,
+      baseURL: baseUrl,
       headers,
       name: 'github-copilot',
     })
 
     return new AiSdkContentGenerator({
+      charsPerToken: isCopilotClaudeModel(config.model) ? 3.5 : undefined,
       model: provider.chatModel(config.model),
     })
   },
-  defaultModel: 'claude-sonnet-4',
+  defaultModel: 'claude-sonnet-4.6',
   description: 'All models via GitHub Copilot subscription',
   envVars: [],
   id: 'github-copilot',

src/server/core/domain/entities/provider-registry.ts

@@ -147,7 +147,7 @@ export const PROVIDER_REGISTRY: Readonly<Record<string, ProviderDefinition>> = {
   'github-copilot': {
     baseUrl: 'https://api.githubcopilot.com',
     category: 'popular',
-    defaultModel: 'claude-sonnet-4',
+    defaultModel: 'claude-sonnet-4.6',
     description: 'All models via GitHub Copilot subscription',
     headers: {},
     id: 'github-copilot',

src/shared/constants/copilot.ts

@@ -10,7 +10,7 @@ export const GITHUB_OAUTH_TOKEN_URL = 'https://github.com/login/oauth/access_tok
 /** GitHub Copilot internal token exchange endpoint. */
 export const COPILOT_TOKEN_URL = 'https://api.github.com/copilot_internal/v2/token'
 
-/** Copilot API base URL (serves both OpenAI-compatible and Anthropic-compatible endpoints). */
+/** Copilot API base URL (serves OpenAI-compatible chat completions for all models). */
 export const COPILOT_API_BASE_URL = 'https://api.githubcopilot.com'
 
 /** OAuth scope required for Copilot access. */
@@ -33,8 +33,13 @@ export const GITHUB_API_VERSION = '2025-04-01'
 /** Editor version header value sent with Copilot API requests. */
 export const COPILOT_EDITOR_VERSION = 'vscode/1.99.0'
 
-/** Standard headers required for Copilot API requests. */
+export const COPILOT_EDITOR_PLUGIN_VERSION = 'copilot-chat/0.26.7'
+
 export const COPILOT_REQUEST_HEADERS = {
   'Copilot-Integration-Id': 'vscode-chat',
+  'Editor-Plugin-Version': COPILOT_EDITOR_PLUGIN_VERSION,
   'Editor-Version': COPILOT_EDITOR_VERSION,
+  'openai-intent': 'conversation-panel',
+  'User-Agent': `GitHubCopilotChat/${COPILOT_EDITOR_PLUGIN_VERSION.split('/')[1]}`,
+  'x-github-api-version': GITHUB_API_VERSION,
 } as const

test/unit/core/domain/entities/provider-registry.test.ts

@@ -132,7 +132,7 @@ describe('Provider Registry', () => {
       expect(copilot?.name).to.equal('GitHub Copilot')
       expect(copilot?.baseUrl).to.equal('https://api.githubcopilot.com')
       expect(copilot?.category).to.equal('popular')
-      expect(copilot?.defaultModel).to.equal('claude-sonnet-4')
+      expect(copilot?.defaultModel).to.equal('claude-sonnet-4.6')
       expect(copilot?.priority).to.equal(8)
     })
 

test/unit/infra/llm/providers/github-copilot.test.ts

@@ -25,7 +25,7 @@ describe('GitHub Copilot Provider', () => {
     })
 
     it('should have correct default model', () => {
-      expect(githubCopilotProvider.defaultModel).to.equal('claude-sonnet-4')
+      expect(githubCopilotProvider.defaultModel).to.equal('claude-sonnet-4.6')
     })
 
     it('should have popular category', () => {
@@ -92,30 +92,45 @@ describe('GitHub Copilot Provider', () => {
       })
       expect(generator).to.be.instanceOf(AiSdkContentGenerator)
     })
+
+    it('should use OpenAI-compatible format for all models including Claude', () => {
+      const claudeGen = githubCopilotProvider.createGenerator({
+        ...BASE_FACTORY_CONFIG,
+        apiKey: 'test-token',
+        model: 'claude-sonnet-4',
+      })
+      const gptGen = githubCopilotProvider.createGenerator({
+        ...BASE_FACTORY_CONFIG,
+        apiKey: 'test-token',
+        model: 'gpt-4.1',
+      })
+      expect(claudeGen).to.be.instanceOf(AiSdkContentGenerator)
+      expect(gptGen).to.be.instanceOf(AiSdkContentGenerator)
+    })
   })
 
-  describe('model routing', () => {
-    it('should route claude-sonnet-4 as Claude model', () => {
+  describe('isCopilotClaudeModel()', () => {
+    it('should return true for claude-sonnet-4', () => {
       expect(isCopilotClaudeModel('claude-sonnet-4')).to.be.true
     })
 
-    it('should route claude-opus-4.5 as Claude model', () => {
+    it('should return true for claude-opus-4.5', () => {
       expect(isCopilotClaudeModel('claude-opus-4.5')).to.be.true
     })
 
-    it('should route claude-haiku-4.5 as Claude model', () => {
+    it('should return true for claude-haiku-4.5', () => {
       expect(isCopilotClaudeModel('claude-haiku-4.5')).to.be.true
     })
 
-    it('should route gpt-4.1 as non-Claude model', () => {
+    it('should return false for gpt-4.1', () => {
       expect(isCopilotClaudeModel('gpt-4.1')).to.be.false
     })
 
-    it('should route gemini-2.5-pro as non-Claude model', () => {
+    it('should return false for gemini-2.5-pro', () => {
       expect(isCopilotClaudeModel('gemini-2.5-pro')).to.be.false
     })
 
-    it('should route o3 as non-Claude model', () => {
+    it('should return false for o3', () => {
       expect(isCopilotClaudeModel('o3')).to.be.false
     })
   })

test/unit/infra/provider/provider-config-resolver.test.ts

@@ -438,7 +438,11 @@ describe('provider-config-resolver', () => {
       expect(result.providerBaseUrl).to.equal('https://api.githubcopilot.com')
       expect(result.providerHeaders).to.deep.equal({
         'Copilot-Integration-Id': 'vscode-chat',
+        'Editor-Plugin-Version': 'copilot-chat/0.26.7',
         'Editor-Version': 'vscode/1.99.0',
+        'openai-intent': 'conversation-panel',
+        'User-Agent': 'GitHubCopilotChat/0.26.7',
+        'x-github-api-version': '2025-04-01',
       })
       expect(result.providerKeyMissing).to.be.false
     })