diff --git a/src/utils/model/model.ts b/src/utils/model/model.ts
index 6ccb72510..a43d101bb 100644
--- a/src/utils/model/model.ts
+++ b/src/utils/model/model.ts
@@ -24,7 +24,7 @@ import { getModelStrings, resolveOverriddenModel } from './modelStrings.js'
 import { formatModelPricing, getOpus46CostTier } from '../modelCost.js'
 import { getSettings_DEPRECATED } from '../settings/settings.js'
 import type { PermissionMode } from '../permissions/PermissionMode.js'
-import { getAPIProvider } from './providers.js'
+import { getAPIProvider, isFirstPartyAnthropicBaseUrl } from './providers.js'
 import { LIGHTNING_BOLT } from '../../constants/figures.js'
 import { isModelAllowed } from './modelAllowlist.js'
 import { type ModelAlias, isModelAlias } from './aliases.js'
@@ -360,7 +360,8 @@ export function isOpus1mMergeEnabled(): boolean {
   if (
     is1mContextDisabled() ||
     isProSubscriber() ||
-    getAPIProvider() !== 'firstParty'
+    getAPIProvider() !== 'firstParty' ||
+    !isFirstPartyAnthropicBaseUrl()
   ) {
     return false
   }