diff --git a/backend/internal/service/openai_gateway_service.go b/backend/internal/service/openai_gateway_service.go
index 04ea2930..6d93e92d 100644
--- a/backend/internal/service/openai_gateway_service.go
+++ b/backend/internal/service/openai_gateway_service.go
@@ -845,6 +845,12 @@ func (s *OpenAIGatewayService) Forward(ctx context.Context, c *gin.Context, acco
 				bodyModified = true
 			}
 		}
+
+		// Remove prompt_cache_retention (not supported by upstream OpenAI API)
+		if _, has := reqBody["prompt_cache_retention"]; has {
+			delete(reqBody, "prompt_cache_retention")
+			bodyModified = true
+		}
 	}
 
 	// Re-serialize body only if modified
diff --git a/frontend/src/components/account/CreateAccountModal.vue b/frontend/src/components/account/CreateAccountModal.vue
index 144241ff..998a594d 100644
--- a/frontend/src/components/account/CreateAccountModal.vue
+++ b/frontend/src/components/account/CreateAccountModal.vue
@@ -1799,6 +1799,18 @@
       </div>
     </template>
   </BaseDialog>
+
+  <!-- Mixed Channel Warning Dialog -->
+  <ConfirmDialog
+    :show="showMixedChannelWarning"
+    :title="t('admin.accounts.mixedChannelWarningTitle')"
+    :message="mixedChannelWarningDetails ? t('admin.accounts.mixedChannelWarning', mixedChannelWarningDetails) : ''"
+    :confirm-text="t('common.confirm')"
+    :cancel-text="t('common.cancel')"
+    :danger="true"
+    @confirm="handleMixedChannelConfirm"
+    @cancel="handleMixedChannelCancel"
+  />
 </template>
 
 <script setup lang="ts">
@@ -1818,6 +1830,7 @@ import { useGeminiOAuth } from '@/composables/useGeminiOAuth'
 import { useAntigravityOAuth } from '@/composables/useAntigravityOAuth'
 import type { Proxy, AdminGroup, AccountPlatform, AccountType } from '@/types'
 import BaseDialog from '@/components/common/BaseDialog.vue'
+import ConfirmDialog from '@/components/common/ConfirmDialog.vue'
 import Icon from '@/components/icons/Icon.vue'
 import ProxySelector from '@/components/common/ProxySelector.vue'
 import GroupSelector from '@/components/common/GroupSelector.vue'
@@ -1944,6 +1957,11 @@ const tempUnschedEnabled = ref(false)
 const tempUnschedRules = ref<TempUnschedRuleForm[]>([])
 const geminiOAuthType = ref<'code_assist' | 'google_one' | 'ai_studio'>('google_one')
 const geminiAIStudioOAuthEnabled = ref(false)
+
+// Mixed channel warning dialog state
+const showMixedChannelWarning = ref(false)
+const mixedChannelWarningDetails = ref<{ groupName: string; currentPlatform: string; otherPlatform: string } | null>(null)
+const pendingCreatePayload = ref<any>(null)
 const showAdvancedOAuth = ref(false)
 const showGeminiHelpDialog = ref(false)
 
@@ -2360,6 +2378,59 @@ const handleClose = () => {
   emit('close')
 }
 
+// Helper function to create account with mixed channel warning handling
+const doCreateAccount = async (payload: any) => {
+  submitting.value = true
+  try {
+    await adminAPI.accounts.create(payload)
+    appStore.showSuccess(t('admin.accounts.accountCreated'))
+    emit('created')
+    handleClose()
+  } catch (error: any) {
+    // Handle 409 mixed_channel_warning - show confirmation dialog
+    if (error.response?.status === 409 && error.response?.data?.error === 'mixed_channel_warning') {
+      const details = error.response.data.details || {}
+      mixedChannelWarningDetails.value = {
+        groupName: details.group_name || 'Unknown',
+        currentPlatform: details.current_platform || 'Unknown',
+        otherPlatform: details.other_platform || 'Unknown'
+      }
+      pendingCreatePayload.value = payload
+      showMixedChannelWarning.value = true
+    } else {
+      appStore.showError(error.response?.data?.detail || t('admin.accounts.failedToCreate'))
+    }
+  } finally {
+    submitting.value = false
+  }
+}
+
+// Handle mixed channel warning confirmation
+const handleMixedChannelConfirm = async () => {
+  showMixedChannelWarning.value = false
+  if (pendingCreatePayload.value) {
+    pendingCreatePayload.value.confirm_mixed_channel_risk = true
+    submitting.value = true
+    try {
+      await adminAPI.accounts.create(pendingCreatePayload.value)
+      appStore.showSuccess(t('admin.accounts.accountCreated'))
+      emit('created')
+      handleClose()
+    } catch (error: any) {
+      appStore.showError(error.response?.data?.detail || t('admin.accounts.failedToCreate'))
+    } finally {
+      submitting.value = false
+      pendingCreatePayload.value = null
+    }
+  }
+}
+
+const handleMixedChannelCancel = () => {
+  showMixedChannelWarning.value = false
+  pendingCreatePayload.value = null
+  mixedChannelWarningDetails.value = null
+}
+
 const handleSubmit = async () => {
   // For OAuth-based type, handle OAuth flow (goes to step 2)
   if (isOAuthFlow.value) {
@@ -2416,21 +2487,11 @@ const handleSubmit = async () => {
 
   form.credentials = credentials
 
-  submitting.value = true
-  try {
-    await adminAPI.accounts.create({
-      ...form,
-      group_ids: form.group_ids,
-      auto_pause_on_expired: autoPauseOnExpired.value
-    })
-    appStore.showSuccess(t('admin.accounts.accountCreated'))
-    emit('created')
-    handleClose()
-  } catch (error: any) {
-    appStore.showError(error.response?.data?.detail || t('admin.accounts.failedToCreate'))
-  } finally {
-    submitting.value = false
-  }
+  await doCreateAccount({
+    ...form,
+    group_ids: form.group_ids,
+    auto_pause_on_expired: autoPauseOnExpired.value
+  })
 }
 
 const goBackToBasicInfo = () => {
diff --git a/frontend/src/components/account/EditAccountModal.vue b/frontend/src/components/account/EditAccountModal.vue
index 0dd855ef..a5c7aa42 100644
--- a/frontend/src/components/account/EditAccountModal.vue
+++ b/frontend/src/components/account/EditAccountModal.vue
@@ -875,6 +875,18 @@
       </div>
     </template>
   </BaseDialog>
+
+  <!-- Mixed Channel Warning Dialog -->
+  <ConfirmDialog
+    :show="showMixedChannelWarning"
+    :title="t('admin.accounts.mixedChannelWarningTitle')"
+    :message="mixedChannelWarningDetails ? t('admin.accounts.mixedChannelWarning', mixedChannelWarningDetails) : ''"
+    :confirm-text="t('common.confirm')"
+    :cancel-text="t('common.cancel')"
+    :danger="true"
+    @confirm="handleMixedChannelConfirm"
+    @cancel="handleMixedChannelCancel"
+  />
 </template>
 
 <script setup lang="ts">
@@ -885,6 +897,7 @@ import { useAuthStore } from '@/stores/auth'
 import { adminAPI } from '@/api/admin'
 import type { Account, Proxy, AdminGroup } from '@/types'
 import BaseDialog from '@/components/common/BaseDialog.vue'
+import ConfirmDialog from '@/components/common/ConfirmDialog.vue'
 import Select from '@/components/common/Select.vue'
 import Icon from '@/components/icons/Icon.vue'
 import ProxySelector from '@/components/common/ProxySelector.vue'
@@ -951,6 +964,11 @@ const mixedScheduling = ref(false) // For antigravity accounts: enable mixed sch
 const tempUnschedEnabled = ref(false)
 const tempUnschedRules = ref<TempUnschedRuleForm[]>([])
 
+// Mixed channel warning dialog state
+const showMixedChannelWarning = ref(false)
+const mixedChannelWarningDetails = ref<{ groupName: string; currentPlatform: string; otherPlatform: string } | null>(null)
+const pendingUpdatePayload = ref<Record<string, unknown> | null>(null)
+
 // Quota control state (Anthropic OAuth/SetupToken only)
 const windowCostEnabled = ref(false)
 const windowCostLimit = ref<number | null>(null)
@@ -1366,8 +1384,8 @@ const handleSubmit = async () => {
   if (!props.account) return
 
   submitting.value = true
+  const updatePayload: Record<string, unknown> = { ...form }
   try {
-    const updatePayload: Record<string, unknown> = { ...form }
     // 后端期望 proxy_id: 0 表示清除代理，而不是 null
     if (updatePayload.proxy_id === null) {
       updatePayload.proxy_id = 0
@@ -1497,9 +1515,47 @@ const handleSubmit = async () => {
     emit('updated')
     handleClose()
   } catch (error: any) {
-    appStore.showError(error.response?.data?.message || error.response?.data?.detail || t('admin.accounts.failedToUpdate'))
+    // Handle 409 mixed_channel_warning - show confirmation dialog
+    if (error.response?.status === 409 && error.response?.data?.error === 'mixed_channel_warning') {
+      const details = error.response.data.details || {}
+      mixedChannelWarningDetails.value = {
+        groupName: details.group_name || 'Unknown',
+        currentPlatform: details.current_platform || 'Unknown',
+        otherPlatform: details.other_platform || 'Unknown'
+      }
+      pendingUpdatePayload.value = updatePayload
+      showMixedChannelWarning.value = true
+    } else {
+      appStore.showError(error.response?.data?.message || error.response?.data?.detail || t('admin.accounts.failedToUpdate'))
+    }
   } finally {
     submitting.value = false
   }
 }
+
+// Handle mixed channel warning confirmation
+const handleMixedChannelConfirm = async () => {
+  showMixedChannelWarning.value = false
+  if (pendingUpdatePayload.value && props.account) {
+    pendingUpdatePayload.value.confirm_mixed_channel_risk = true
+    submitting.value = true
+    try {
+      await adminAPI.accounts.update(props.account.id, pendingUpdatePayload.value)
+      appStore.showSuccess(t('admin.accounts.accountUpdated'))
+      emit('updated')
+      handleClose()
+    } catch (error: any) {
+      appStore.showError(error.response?.data?.message || error.response?.data?.detail || t('admin.accounts.failedToUpdate'))
+    } finally {
+      submitting.value = false
+      pendingUpdatePayload.value = null
+    }
+  }
+}
+
+const handleMixedChannelCancel = () => {
+  showMixedChannelWarning.value = false
+  pendingUpdatePayload.value = null
+  mixedChannelWarningDetails.value = null
+}
 </script>
diff --git a/frontend/src/i18n/locales/en.ts b/frontend/src/i18n/locales/en.ts
index e9b51b69..abe2ea52 100644
--- a/frontend/src/i18n/locales/en.ts
+++ b/frontend/src/i18n/locales/en.ts
@@ -1432,6 +1432,8 @@ export default {
       accountUpdated: 'Account updated successfully',
       failedToCreate: 'Failed to create account',
       failedToUpdate: 'Failed to update account',
+      mixedChannelWarningTitle: 'Mixed Channel Warning',
+      mixedChannelWarning: 'Warning: Group "{groupName}" contains both {currentPlatform} and {otherPlatform} accounts. Mixing different channels may cause thinking block signature validation issues, which will fallback to non-thinking mode. Are you sure you want to continue?',
       pleaseEnterAccountName: 'Please enter account name',
       pleaseEnterApiKey: 'Please enter API Key',
       apiKeyIsRequired: 'API Key is required',
diff --git a/frontend/src/i18n/locales/zh.ts b/frontend/src/i18n/locales/zh.ts
index d57b4c02..dd0ae0fb 100644
--- a/frontend/src/i18n/locales/zh.ts
+++ b/frontend/src/i18n/locales/zh.ts
@@ -1564,6 +1564,8 @@ export default {
       accountUpdated: '账号更新成功',
       failedToCreate: '创建账号失败',
       failedToUpdate: '更新账号失败',
+      mixedChannelWarningTitle: '混合渠道警告',
+      mixedChannelWarning: '警告：分组 "{groupName}" 中同时包含 {currentPlatform} 和 {otherPlatform} 账号。混合使用不同渠道可能导致 thinking block 签名验证问题，会自动回退到非 thinking 模式。确定要继续吗？',
       pleaseEnterAccountName: '请输入账号名称',
       pleaseEnterApiKey: '请输入 API Key',
       apiKeyIsRequired: 'API Key 是必需的',