diff --git a/packages/shared/anthropic/index.ts b/packages/shared/anthropic/index.ts
index b9e9cb8846..bff143d118 100644
--- a/packages/shared/anthropic/index.ts
+++ b/packages/shared/anthropic/index.ts
@@ -88,11 +88,16 @@ export function getSdkClient(
       }
     })
   }
-  const baseURL =
+  let baseURL =
     provider.type === 'anthropic'
       ? provider.apiHost
       : (provider.anthropicApiHost && provider.anthropicApiHost.trim()) || provider.apiHost
 
+  // Anthropic SDK automatically appends /v1 to all endpoints (like /v1/messages, /v1/models)
+  // We need to strip api version from baseURL to avoid duplication (e.g., /v3/v1/models)
+  // formatProviderApiHost adds /v1 for AI SDK compatibility, but Anthropic SDK needs it removed
+  baseURL = baseURL.replace(/\/v\d+(?:alpha|beta)?(?=\/|$)/i, '')
+
   logger.debug('Anthropic API baseURL', { baseURL, providerId: provider.id })
 
   if (provider.id === 'aihubmix') {
diff --git a/src/renderer/src/aiCore/index_new.ts b/src/renderer/src/aiCore/index_new.ts
index efc9ba992f..cf12a46aa6 100644
--- a/src/renderer/src/aiCore/index_new.ts
+++ b/src/renderer/src/aiCore/index_new.ts
@@ -50,7 +50,40 @@ export default class ModernAiProvider {
   private model?: Model
   private localProvider: Awaited<AiSdkProvider> | null = null
 
-  // 构造函数重载签名
+  /**
+   * Constructor for ModernAiProvider
+   *
+   * @param modelOrProvider - Model or Provider object
+   * @param provider - Optional Provider object (only used when first param is Model)
+   *
+   * @remarks
+   * **Important behavior notes**:
+   *
+   * 1. When called with `(model)`:
+   *    - Calls `getActualProvider(model)` to retrieve and format the provider
+   *    - URL will be automatically formatted via `formatProviderApiHost`, adding version suffixes like `/v1`
+   *
+   * 2. When called with `(model, provider)`:
+   *    - **Directly uses the provided provider WITHOUT going through `getActualProvider`**
+   *    - **URL will NOT be automatically formatted, `/v1` suffix will NOT be added**
+   *    - This is legacy behavior kept for backward compatibility
+   *
+   * 3. When called with `(provider)`:
+   *    - Directly uses the provider without requiring a model
+   *    - Used for operations that don't need a model (e.g., fetchModels)
+   *
+   * @example
+   * ```typescript
+   * // Recommended: Auto-format URL
+   * const ai = new ModernAiProvider(model)
+   *
+   * // Not recommended: Skip URL formatting (only for special cases)
+   * const ai = new ModernAiProvider(model, customProvider)
+   *
+   * // For operations that don't need a model
+   * const ai = new ModernAiProvider(provider)
+   * ```
+   */
   constructor(model: Model, provider?: Provider)
   constructor(provider: Provider)
   constructor(modelOrProvider: Model | Provider, provider?: Provider)
@@ -322,10 +355,10 @@ export default class ModernAiProvider {
     }
   }
 
-  /**
-   * 使用现代化 AI SDK 的图像生成实现，支持流式输出
-   * @deprecated 已改为使用 legacy 实现以支持图片编辑等高级功能
-   */
+  // /**
+  //  * 使用现代化 AI SDK 的图像生成实现，支持流式输出
+  //  * @deprecated 已改为使用 legacy 实现以支持图片编辑等高级功能
+  //  */
   /*
   private async modernImageGeneration(
     model: ImageModel,
diff --git a/src/renderer/src/aiCore/provider/providerConfig.ts b/src/renderer/src/aiCore/provider/providerConfig.ts
index ecc2cd6032..53194d3506 100644
--- a/src/renderer/src/aiCore/provider/providerConfig.ts
+++ b/src/renderer/src/aiCore/provider/providerConfig.ts
@@ -90,6 +90,7 @@ function formatProviderApiHost(provider: Provider): Provider {
 
   if (isAnthropicProvider(provider)) {
     const baseHost = formatted.anthropicApiHost || formatted.apiHost
+    // AI SDK needs /v1 in baseURL, Anthropic SDK will strip it in getSdkClient
     formatted.apiHost = formatApiHost(baseHost)
     if (!formatted.anthropicApiHost) {
       formatted.anthropicApiHost = formatted.apiHost
diff --git a/src/renderer/src/pages/settings/ProviderSettings/ProviderSetting.tsx b/src/renderer/src/pages/settings/ProviderSettings/ProviderSetting.tsx
index b1cbb9be6c..f341ac9229 100644
--- a/src/renderer/src/pages/settings/ProviderSettings/ProviderSetting.tsx
+++ b/src/renderer/src/pages/settings/ProviderSettings/ProviderSetting.tsx
@@ -298,7 +298,10 @@ const ProviderSetting: FC<Props> = ({ providerId }) => {
     }
 
     if (isAnthropicProvider(provider)) {
-      return formatApiHost(apiHost) + '/messages'
+      // AI SDK uses the baseURL with /v1, then appends /messages
+      // formatApiHost adds /v1 automatically if not present
+      const normalizedHost = formatApiHost(apiHost)
+      return normalizedHost + '/messages'
     }
 
     if (isGeminiProvider(provider)) {
@@ -351,6 +354,7 @@ const ProviderSetting: FC<Props> = ({ providerId }) => {
 
   const anthropicHostPreview = useMemo(() => {
     const rawHost = anthropicApiHost ?? provider.anthropicApiHost
+    // AI SDK uses the baseURL with /v1, then appends /messages
     const normalizedHost = formatApiHost(rawHost)
 
     return `${normalizedHost}/messages`
diff --git a/src/renderer/src/services/ApiService.ts b/src/renderer/src/services/ApiService.ts
index f19c90b61f..1b2bf0433f 100644
--- a/src/renderer/src/services/ApiService.ts
+++ b/src/renderer/src/services/ApiService.ts
@@ -2,8 +2,6 @@
  * 职责：提供原子化的、无状态的API调用函数
  */
 import { loggerService } from '@logger'
-import AiProvider from '@renderer/aiCore'
-import type { CompletionsParams } from '@renderer/aiCore/legacy/middleware/schemas'
 import type { AiSdkMiddlewareConfig } from '@renderer/aiCore/middleware/AiSdkMiddlewareBuilder'
 import { buildStreamTextParams } from '@renderer/aiCore/prepareParams'
 import { isDedicatedImageGenerationModel, isEmbeddingModel, isFunctionCallingModel } from '@renderer/config/models'
@@ -463,76 +461,55 @@ export function checkApiProvider(provider: Provider): void {
 export async function checkApi(provider: Provider, model: Model, timeout = 15000): Promise<void> {
   checkApiProvider(provider)
 
+  // Don't pass in provider parameter. We need auto-format URL
   const ai = new AiProviderNew(model)
 
   const assistant = getDefaultAssistant()
   assistant.model = model
   assistant.prompt = 'test' // 避免部分 provider 空系统提示词会报错
-  try {
-    if (isEmbeddingModel(model)) {
-      // race 超时 15s
-      logger.silly("it's a embedding model")
-      const timerPromise = new Promise((_, reject) => setTimeout(() => reject('Timeout'), timeout))
-      await Promise.race([ai.getEmbeddingDimensions(model), timerPromise])
-    } else {
-      const abortId = uuid()
-      const signal = readyToAbort(abortId)
-      let chunkError
-      const params: StreamTextParams = {
-        system: assistant.prompt,
-        prompt: 'hi',
-        abortSignal: signal
-      }
-      const config: ModernAiProviderConfig = {
-        streamOutput: true,
-        enableReasoning: false,
-        isSupportedToolUse: false,
-        isImageGenerationEndpoint: false,
-        enableWebSearch: false,
-        enableGenerateImage: false,
-        isPromptToolUse: false,
-        enableUrlContext: false,
-        assistant,
-        callType: 'check',
-        onChunk: (chunk: Chunk) => {
-          if (chunk.type === ChunkType.ERROR) {
-            chunkError = chunk.error
-          } else {
-            abortCompletion(abortId)
-          }
-        }
-      }
 
-      // Try streaming check first
-      try {
-        await ai.completions(model.id, params, config)
-      } catch (e) {
-        if (!isAbortError(e) && !isAbortError(chunkError)) {
-          throw e
+  if (isEmbeddingModel(model)) {
+    // race 超时 15s
+    logger.silly("it's a embedding model")
+    const timerPromise = new Promise((_, reject) => setTimeout(() => reject('Timeout'), timeout))
+    await Promise.race([ai.getEmbeddingDimensions(model), timerPromise])
+  } else {
+    const abortId = uuid()
+    const signal = readyToAbort(abortId)
+    let chunkError
+    const params: StreamTextParams = {
+      system: assistant.prompt,
+      prompt: 'hi',
+      abortSignal: signal
+    }
+    const config: ModernAiProviderConfig = {
+      streamOutput: true,
+      enableReasoning: false,
+      isSupportedToolUse: false,
+      isImageGenerationEndpoint: false,
+      enableWebSearch: false,
+      enableGenerateImage: false,
+      isPromptToolUse: false,
+      enableUrlContext: false,
+      assistant,
+      callType: 'check',
+      onChunk: (chunk: Chunk) => {
+        if (chunk.type === ChunkType.ERROR) {
+          chunkError = chunk.error
+        } else {
+          abortCompletion(abortId)
         }
       }
     }
-  } catch (error: any) {
-    // 失败回退legacy
-    const legacyAi = new AiProvider(provider)
-    if (error.message.includes('stream')) {
-      const params: CompletionsParams = {
-        callType: 'check',
-        messages: 'hi',
-        assistant,
-        streamOutput: false,
-        shouldThrow: true
+
+    // Try streaming check
+    try {
+      await ai.completions(model.id, params, config)
+    } catch (e) {
+      if (!isAbortError(e) && !isAbortError(chunkError)) {
+        throw e
       }
-      const result = await legacyAi.completions(params)
-      if (!result.getText()) {
-        throw new Error('No response received')
-      }
-    } else {
-      throw error
     }
-    // } finally {
-    //   removeAbortController(taskId, abortFn)
-    // }
   }
 }