diff --git a/src/renderer/src/aiCore/legacy/clients/__tests__/OpenAIAPIClient.reasoning.test.ts b/src/renderer/src/aiCore/legacy/clients/__tests__/OpenAIAPIClient.reasoning.test.ts
new file mode 100644
index 0000000000..bc9bb3b8a0
--- /dev/null
+++ b/src/renderer/src/aiCore/legacy/clients/__tests__/OpenAIAPIClient.reasoning.test.ts
@@ -0,0 +1,219 @@
+import type { Assistant, Model, Provider } from '@renderer/types'
+import { beforeEach, describe, expect, it, vi } from 'vitest'
+
+import { OpenAIAPIClient } from '../openai/OpenAIApiClient'
+
+// Mock dependencies
+vi.mock('@renderer/config/models', () => ({
+  isSupportedReasoningEffortOpenAIModel: vi.fn((model: Model) => {
+    const modelId = model.id.toLowerCase()
+    return (
+      modelId.includes('gpt-5') ||
+      (modelId.includes('o1') && !modelId.includes('o1-preview') && !modelId.includes('o1-mini')) ||
+      modelId.includes('o3') ||
+      modelId.includes('o4')
+    )
+  }),
+  isSupportedReasoningEffortGrokModel: vi.fn((model: Model) => {
+    return model.id.toLowerCase().includes('grok')
+  }),
+  isSupportedReasoningEffortPerplexityModel: vi.fn((model: Model) => {
+    return model.id.toLowerCase().includes('sonar-deep-research')
+  }),
+  isSupportedReasoningEffortModel: vi.fn((model: Model) => {
+    const modelId = model.id.toLowerCase()
+    return (
+      modelId.includes('gpt-5') ||
+      modelId.includes('o1') ||
+      modelId.includes('o3') ||
+      modelId.includes('o4') ||
+      modelId.includes('grok') ||
+      modelId.includes('sonar-deep-research')
+    )
+  }),
+  isReasoningModel: vi.fn(() => true),
+  isOpenAIDeepResearchModel: vi.fn(() => false),
+  isSupportedThinkingTokenZhipuModel: vi.fn(() => false),
+  isDeepSeekHybridInferenceModel: vi.fn(() => false),
+  isSupportedThinkingTokenGeminiModel: vi.fn(() => false),
+  isSupportedThinkingTokenQwenModel: vi.fn(() => false),
+  isSupportedThinkingTokenHunyuanModel: vi.fn(() => false),
+  isSupportedThinkingTokenClaudeModel: vi.fn(() => false),
+  isSupportedThinkingTokenDoubaoModel: vi.fn(() => false),
+  isQwenReasoningModel: vi.fn(() => false),
+  isGrokReasoningModel: vi.fn(() => false),
+  isOpenAIReasoningModel: vi.fn(() => false),
+  isSupportedThinkingTokenModel: vi.fn(() => false),
+  isQwenAlwaysThinkModel: vi.fn(() => false),
+  isDoubaoThinkingAutoModel: vi.fn(() => false),
+  getThinkModelType: vi.fn(() => 'default'),
+  GEMINI_FLASH_MODEL_REGEX: /gemini.*flash/i,
+  MODEL_SUPPORTED_REASONING_EFFORT: {
+    default: ['low', 'medium', 'high'],
+    grok: ['low', 'high'],
+    perplexity: ['low', 'medium', 'high'],
+    gpt5: ['minimal', 'low', 'medium', 'high']
+  },
+  findTokenLimit: vi.fn()
+}))
+
+vi.mock('@renderer/config/providers', () => ({
+  isSupportEnableThinkingProvider: vi.fn(() => false)
+}))
+
+vi.mock('@renderer/hooks/useSettings', () => ({
+  getStoreSetting: vi.fn(() => ({
+    summaryText: 'off'
+  }))
+}))
+
+vi.mock('@renderer/types', () => ({
+  SystemProviderIds: {
+    groq: 'groq',
+    openrouter: 'openrouter',
+    dashscope: 'dashscope',
+    doubao: 'doubao',
+    silicon: 'silicon',
+    ppio: 'ppio',
+    poe: 'poe'
+  },
+  EFFORT_RATIO: {
+    minimal: 0.1,
+    low: 0.3,
+    medium: 0.5,
+    high: 0.8,
+    auto: 1
+  }
+}))
+
+describe('OpenAIAPIClient - Reasoning Effort', () => {
+  let client: OpenAIAPIClient
+  let provider: Provider
+  let assistant: Assistant
+  
+  beforeEach(() => {
+    provider = {
+      id: 'copilot',
+      name: 'Github Copilot',
+      type: 'openai',
+      apiKey: 'test-key',
+      apiHost: 'https://api.githubcopilot.com/',
+      models: []
+    }
+    
+    client = new OpenAIAPIClient(provider)
+    
+    assistant = {
+      id: 'test-assistant',
+      name: 'Test Assistant',
+      emoji: '🤖',
+      prompt: 'You are a helpful assistant',
+      topics: [],
+      messages: [],
+      type: 'assistant',
+      regularPhrases: [],
+      settings: {
+        reasoning_effort: 'medium'
+      }
+    }
+  })
+
+  describe('GPT-5 models through GitHub Copilot', () => {
+    it('should return reasoning object format for gpt-5-mini', () => {
+      const model: Model = {
+        id: 'gpt-5-mini',
+        name: 'GPT-5 Mini',
+        provider: 'copilot',
+        group: 'openai'
+      }
+
+      const result = client.getReasoningEffort(assistant, model)
+
+      // Should use base class implementation which returns { reasoning: { effort, summary } }
+      expect(result).toHaveProperty('reasoning')
+      expect(result.reasoning).toHaveProperty('effort', 'medium')
+      expect(result.reasoning).toHaveProperty('summary')
+      expect(result).not.toHaveProperty('reasoning_effort')
+    })
+
+    it('should return reasoning object format for o1-2024-12-17', () => {
+      const model: Model = {
+        id: 'o1-2024-12-17',
+        name: 'O1',
+        provider: 'copilot',
+        group: 'openai'
+      }
+
+      const result = client.getReasoningEffort(assistant, model)
+
+      expect(result).toHaveProperty('reasoning')
+      expect(result.reasoning).toHaveProperty('effort', 'medium')
+      expect(result).not.toHaveProperty('reasoning_effort')
+    })
+
+    it('should return reasoning object format for o3-mini', () => {
+      const model: Model = {
+        id: 'o3-mini',
+        name: 'O3 Mini',
+        provider: 'copilot',
+        group: 'openai'
+      }
+
+      const result = client.getReasoningEffort(assistant, model)
+
+      expect(result).toHaveProperty('reasoning')
+      expect(result.reasoning).toHaveProperty('effort', 'medium')
+      expect(result).not.toHaveProperty('reasoning_effort')
+    })
+  })
+
+  describe('Non-OpenAI reasoning models', () => {
+    it('should return reasoning_effort format for Grok models', () => {
+      const model: Model = {
+        id: 'grok-3-mini',
+        name: 'Grok 3 Mini',
+        provider: 'grok',
+        group: 'xai'
+      }
+
+      const result = client.getReasoningEffort(assistant, model)
+
+      // Should use reasoning_effort for non-OpenAI models
+      expect(result).toHaveProperty('reasoning_effort', 'medium')
+      expect(result).not.toHaveProperty('reasoning')
+    })
+
+    it('should return reasoning_effort format for Perplexity models', () => {
+      const model: Model = {
+        id: 'sonar-deep-research',
+        name: 'Sonar Deep Research',
+        provider: 'perplexity',
+        group: 'perplexity'
+      }
+
+      const result = client.getReasoningEffort(assistant, model)
+
+      expect(result).toHaveProperty('reasoning_effort', 'medium')
+      expect(result).not.toHaveProperty('reasoning')
+    })
+  })
+
+  describe('When reasoning_effort is not set', () => {
+    beforeEach(() => {
+      assistant.settings = {}
+    })
+
+    it('should return empty object for GPT-5 models', () => {
+      const model: Model = {
+        id: 'gpt-5-mini',
+        name: 'GPT-5 Mini',
+        provider: 'copilot',
+        group: 'openai'
+      }
+
+      const result = client.getReasoningEffort(assistant, model)
+
+      expect(result).toEqual({})
+    })
+  })
+})