diff --git a/api/db/joint_services/tenant_model_service.py b/api/db/joint_services/tenant_model_service.py
index 785312032e..425ff459ce 100644
--- a/api/db/joint_services/tenant_model_service.py
+++ b/api/db/joint_services/tenant_model_service.py
@@ -435,6 +435,37 @@ def ensure_tenant_model_ids_for_params(tenant_id: str, params: dict) -> dict:
 
 
 def get_api_key(tenant_id: str, model_name: str):
+    # Try direct model ID (UUID) lookup first
+    exist, model_obj = TenantModelService.get_by_id(model_name)
+    if exist:
+        # Verify tenant ownership through the provider chain
+        ok, provider_obj = TenantModelProviderService.get_by_id(model_obj.provider_id)
+        if not ok:
+            raise LookupError(f"Provider id={model_obj.provider_id} not found for model {model_name}.")
+        if tenant_id != provider_obj.tenant_id:
+            joined_tenants = TenantService.get_joined_tenants_by_user_id(tenant_id)
+            joined_tenant_ids = [t["tenant_id"] for t in joined_tenants]
+            if provider_obj.tenant_id not in joined_tenant_ids:
+                raise LookupError(f"Tenant {tenant_id} has no access to provider owned by tenant {provider_obj.tenant_id}.")
+
+        exist_inst, instance_obj = TenantModelInstanceService.get_by_id(model_obj.instance_id)
+        if not exist_inst:
+            logger.warning(
+                "Direct-ID resolution: instance not found | tenant_id=%s model_id=%s instance_id=%s",
+                tenant_id,
+                model_name,
+                model_obj.instance_id,
+            )
+            raise LookupError(f"Instance {model_obj.instance_id} not found for model {model_name}.")
+        logger.debug(
+            "Direct-ID resolution: resolved | tenant_id=%s model_id=%s instance_id=%s",
+            tenant_id,
+            model_name,
+            model_obj.instance_id,
+        )
+        return instance_obj.api_key
+
+    # Fall back to name-based resolution: model[@instance]@provider
     _, instance_name, provider_name = split_model_name(model_name)
 
     if not provider_name:
diff --git a/web/src/pages/next-chats/chat/chat-box/next-multiple-chat-box.tsx b/web/src/pages/next-chats/chat/chat-box/next-multiple-chat-box.tsx
index c8a83ca7f1..0d73c8bda0 100644
--- a/web/src/pages/next-chats/chat/chat-box/next-multiple-chat-box.tsx
+++ b/web/src/pages/next-chats/chat/chat-box/next-multiple-chat-box.tsx
@@ -39,6 +39,7 @@ import {
   useCallback,
   useEffect,
   useImperativeHandle,
+  useLayoutEffect,
   useRef,
   useState,
 } from 'react';
@@ -60,7 +61,6 @@ import { useUploadFile } from '../../hooks/use-upload-file';
 import { buildMessageItemReference } from '../../utils';
 import { useAddChatBox } from '../use-add-box';
 import { useShowInternet } from '../use-show-internet';
-import { useSetDefaultModel } from './use-set-default-model';
 
 type MultipleChatBoxProps = {
   controller: AbortController;
@@ -153,7 +153,9 @@ const ChatCard = forwardRef(function ChatCard(
   const { data: currentDialog } = useFetchChat();
   const findLlmByUuid = useFindLlmByUuid();
 
-  useSetDefaultModel(form);
+  useLayoutEffect(() => {
+    form.setValue('llm_id', currentDialog?.llm_id || '');
+  }, [currentDialog?.llm_id, form]);
 
   const isLatestChat = idx === chatBoxIds.length - 1;
 
diff --git a/web/src/pages/next-chats/chat/chat-box/use-set-default-model.ts b/web/src/pages/next-chats/chat/chat-box/use-set-default-model.ts
deleted file mode 100644
index 6ea8807ae0..0000000000
--- a/web/src/pages/next-chats/chat/chat-box/use-set-default-model.ts
+++ /dev/null
@@ -1,26 +0,0 @@
-import { ModelTypeMap } from '@/components/model-tree-select';
-import { useFetchAllAddedModels } from '@/hooks/use-llm-request';
-import { getRealModelName } from '@/utils/llm-util';
-import { useEffect, useRef } from 'react';
-import { UseFormReturn } from 'react-hook-form';
-
-export function useSetDefaultModel(form: UseFormReturn<any>) {
-  const { data: allAddedModels } = useFetchAllAddedModels();
-  const hasSet = useRef(false);
-
-  useEffect(() => {
-    if (hasSet.current || !allAddedModels.length) return;
-    const chatModels = allAddedModels.filter((m) =>
-      m.model_type?.some((t) => ModelTypeMap.llm_id.includes(t)),
-    );
-    const first = chatModels[0];
-    if (first) {
-      const modelName = getRealModelName(first.name);
-      form.setValue(
-        'llm_id',
-        `${modelName}@${first.instance_name}@${first.provider_name}`,
-      );
-      hasSet.current = true;
-    }
-  }, [allAddedModels, form]);
-}