diff --git a/src/server/__tests__/providers.test.ts b/src/server/__tests__/providers.test.ts
index 6ed3ecae..7381db61 100644
--- a/src/server/__tests__/providers.test.ts
+++ b/src/server/__tests__/providers.test.ts
@@ -1054,6 +1054,47 @@ describe('ProviderService', () => {
         globalThis.fetch = originalFetch
       }
     })
+
+    test('normalizes context-window suffixes before forwarding OpenAI Chat proxy requests', async () => {
+      const originalFetch = globalThis.fetch
+      const calls: Array<{ body: Record<string, unknown> }> = []
+      globalThis.fetch = mock(async (_url: string | URL | Request, init?: RequestInit) => {
+        calls.push({ body: JSON.parse(String(init?.body)) as Record<string, unknown> })
+        return new Response(JSON.stringify({
+          id: 'chatcmpl-1',
+          object: 'chat.completion',
+          created: 0,
+          model: 'mimo-v2.5-pro',
+          choices: [{ index: 0, message: { role: 'assistant', content: 'ok' }, finish_reason: 'stop' }],
+          usage: { prompt_tokens: 1, completion_tokens: 1, total_tokens: 2 },
+        }), {
+          status: 200,
+          headers: { 'Content-Type': 'application/json' },
+        })
+      }) as typeof fetch
+
+      try {
+        const svc = new ProviderService()
+        const provider = await svc.addProvider(sampleInput({ apiFormat: 'openai_chat' }))
+        await svc.activateProvider(provider.id)
+
+        const req = new Request('http://localhost:3456/proxy/v1/messages', {
+          method: 'POST',
+          headers: { 'Content-Type': 'application/json' },
+          body: JSON.stringify({
+            model: 'mimo-v2.5-pro[1m]',
+            max_tokens: 64,
+            messages: [{ role: 'user', content: 'hello from proxy' }],
+          }),
+        })
+
+        const res = await handleProxyRequest(req, new URL(req.url))
+        expect(res.status).toBe(200)
+        expect(calls[0].body.model).toBe('mimo-v2.5-pro')
+      } finally {
+        globalThis.fetch = originalFetch
+      }
+    })
   })
 
   describe('testProvider', () => {
@@ -1151,6 +1192,77 @@ describe('ProviderService', () => {
       }
     })
 
+    test('normalizes context-window suffixes for Anthropic-compatible connectivity tests', async () => {
+      const originalFetch = globalThis.fetch
+      const calls: Array<{ body: Record<string, unknown> }> = []
+      globalThis.fetch = mock(async (_url: string | URL | Request, init?: RequestInit) => {
+        calls.push({ body: JSON.parse(String(init?.body)) as Record<string, unknown> })
+        return new Response(JSON.stringify({
+          type: 'message',
+          model: 'mimo-v2.5-pro',
+          content: [],
+        }), {
+          status: 200,
+          headers: { 'Content-Type': 'application/json' },
+        })
+      }) as typeof fetch
+
+      try {
+        const svc = new ProviderService()
+        const result = await svc.testProviderConfig({
+          baseUrl: 'https://api.xiaomimimo.com/anthropic',
+          apiKey: 'sk-api',
+          modelId: 'mimo-v2.5-pro[1m]',
+          authStrategy: 'auth_token',
+          apiFormat: 'anthropic',
+        })
+
+        expect(result.connectivity.success).toBe(true)
+        expect(result.connectivity.modelUsed).toBe('mimo-v2.5-pro')
+        expect(calls[0].body.model).toBe('mimo-v2.5-pro')
+      } finally {
+        globalThis.fetch = originalFetch
+      }
+    })
+
+    test('normalizes context-window suffixes for provider proxy pipeline tests', async () => {
+      const originalFetch = globalThis.fetch
+      const calls: Array<{ body: Record<string, unknown> }> = []
+      globalThis.fetch = mock(async (_url: string | URL | Request, init?: RequestInit) => {
+        calls.push({ body: JSON.parse(String(init?.body)) as Record<string, unknown> })
+        return new Response(JSON.stringify({
+          id: 'chatcmpl-1',
+          object: 'chat.completion',
+          created: 0,
+          model: 'mimo-v2.5-pro',
+          choices: [{ index: 0, message: { role: 'assistant', content: 'ok' }, finish_reason: 'stop' }],
+          usage: { prompt_tokens: 1, completion_tokens: 1, total_tokens: 2 },
+        }), {
+          status: 200,
+          headers: { 'Content-Type': 'application/json' },
+        })
+      }) as typeof fetch
+
+      try {
+        const svc = new ProviderService()
+        const result = await svc.testProviderConfig({
+          baseUrl: 'https://api.example.com',
+          apiKey: 'sk-api',
+          modelId: 'mimo-v2.5-pro[1m]',
+          authStrategy: 'api_key',
+          apiFormat: 'openai_chat',
+        })
+
+        expect(result.connectivity.success).toBe(true)
+        expect(result.proxy?.success).toBe(true)
+        expect(result.connectivity.modelUsed).toBe('mimo-v2.5-pro')
+        expect(result.proxy?.modelUsed).toBe('mimo-v2.5-pro')
+        expect(calls.map((call) => call.body.model)).toEqual(['mimo-v2.5-pro', 'mimo-v2.5-pro'])
+      } finally {
+        globalThis.fetch = originalFetch
+      }
+    })
+
     test('should use configured network timeout for provider tests', async () => {
       await fs.writeFile(
         path.join(tmpDir, 'settings.json'),
diff --git a/src/server/proxy/handler.ts b/src/server/proxy/handler.ts
index 5a8112de..2a1583ac 100644
--- a/src/server/proxy/handler.ts
+++ b/src/server/proxy/handler.ts
@@ -21,6 +21,7 @@ import { openaiResponsesStreamToAnthropic } from './streaming/openaiResponsesStr
 import type { AnthropicRequest } from './transform/types.js'
 import { getProxyFetchOptions } from '../../utils/proxy.js'
 import { getManualNetworkProxyUrl, loadNetworkSettings } from '../services/networkSettings.js'
+import { normalizeModelStringForAPI } from '../../utils/model/model.js'
 
 const providerService = new ProviderService()
 
@@ -127,7 +128,10 @@ export async function handleProxyRequest(req: Request, url: URL): Promise<Respon
     )
   }
 
-  body = ensureClaudeCodeAttribution(body)
+  body = ensureClaudeCodeAttribution({
+    ...body,
+    model: normalizeModelStringForAPI(body.model),
+  })
 
   const isStream = body.stream === true
   const baseUrl = config.baseUrl.replace(/\/+$/, '')
diff --git a/src/server/services/providerService.ts b/src/server/services/providerService.ts
index 940c069c..7d43fc33 100644
--- a/src/server/services/providerService.ts
+++ b/src/server/services/providerService.ts
@@ -41,6 +41,7 @@ import {
   loadNetworkSettings,
   type NetworkSettings,
 } from './networkSettings.js'
+import { normalizeModelStringForAPI } from '../../utils/model/model.js'
 import type {
   SavedProvider,
   ProvidersIndex,
@@ -445,11 +446,12 @@ export class ProviderService {
     const format: ApiFormat = input.apiFormat ?? 'anthropic'
     const authStrategy = input.authStrategy ?? 'api_key'
     const base = input.baseUrl.replace(/\/+$/, '')
+    const modelId = normalizeModelStringForAPI(input.modelId)
     const networkSettings = await loadNetworkSettings()
 
     // ── Step 1: Basic connectivity ───────────────────────────
     // Directly call the upstream API to verify URL, key, and model.
-    const step1 = await this.testConnectivity(base, input.apiKey, input.modelId, format, authStrategy, networkSettings)
+    const step1 = await this.testConnectivity(base, input.apiKey, modelId, format, authStrategy, networkSettings)
 
     // If connectivity failed, no point running step 2
     if (!step1.success) {
@@ -463,7 +465,7 @@ export class ProviderService {
 
     // ── Step 2: Full proxy pipeline ──────────────────────────
     // Anthropic request → transform → upstream → transform back → validate
-    const step2 = await this.testProxyPipeline(base, input.apiKey, input.modelId, format, networkSettings)
+    const step2 = await this.testProxyPipeline(base, input.apiKey, modelId, format, networkSettings)
 
     return { connectivity: step1, proxy: step2 }
   }