diff --git a/frontend/src/app/workspace/chats/[thread_id]/page.tsx b/frontend/src/app/workspace/chats/[thread_id]/page.tsx
index c4740f15..f5144bae 100644
--- a/frontend/src/app/workspace/chats/[thread_id]/page.tsx
+++ b/frontend/src/app/workspace/chats/[thread_id]/page.tsx
@@ -80,20 +80,19 @@ export default function ChatPage() {
       }, 100);
     }
   }, [inputInitialValue]);
-  const isNewThread = useMemo(
-    () => {
-      if (threadIdFromPath !== "new") {
-        return false;
-      }
+  // UI mode depends only on route: /workspace/chats/new is always "new page" mode.
+  const isNewThread = useMemo(() => threadIdFromPath === "new", [threadIdFromPath]);
 
-      const queryThreadId = searchParams.get("thread_id")?.trim();
-      const queryIsNew = searchParams.get("isnew")?.trim().toLowerCase();
-      const shouldReuseExisting = queryIsNew === "false" && !!queryThreadId;
+  // Submission strategy is controlled by `isnew` query param only.
+  // - isnew=false: reuse existing thread
+  // - otherwise: create/start a new session
+  const createNewSession = useMemo(() => {
+    if (threadIdFromPath !== "new") {
+      return false;
+    }
 
-      return !shouldReuseExisting;
-    },
-    [threadIdFromPath, searchParams],
-  );
+    return searchParams.get("isnew")?.trim().toLowerCase() !== "false";
+  }, [threadIdFromPath, searchParams]);
 
   const uploadTarget = useMemo(() => {
     const target = searchParams.get("upload_target")?.trim().toLowerCase();
@@ -110,11 +109,21 @@ export default function ChatPage() {
     }
   }, [threadIdFromPath, searchParams]);
 
+  // Runtime strategy for /new page:
+  // - UI remains new-page mode
+  // - if isnew=false, execute against existing thread_id without creating a new one
+  const reuseExistingThread = useMemo(
+    () => threadIdFromPath === "new" && !createNewSession && !!threadId,
+    [threadIdFromPath, createNewSession, threadId],
+  );
+
   const { showNotification } = useNotification();
   const [finalState, setFinalState] = useState<AgentThreadState | null>(null);
   const thread = useThreadStream({
-    isNewThread,
+    // Keep UI in new-page mode, but runtime may reuse existing thread
+    isNewThread: reuseExistingThread ? false : isNewThread,
     threadId,
+    fetchStateHistory: true,
     onFinish: (state) => {
       setFinalState(state);
       if (document.hidden || !document.hasFocus()) {
@@ -150,13 +159,16 @@ export default function ChatPage() {
     return result;
   }, [thread, isNewThread]);
 
+  const [hasSubmitted, setHasSubmitted] = useState(false);
+  const suppressExistingThreadPrefetchUi = reuseExistingThread && !hasSubmitted;
+
   useEffect(() => {
     const pageTitle = isNewThread
       ? t.pages.newChat
       : thread.values?.title && thread.values.title !== "Untitled"
         ? thread.values.title
         : t.pages.untitled;
-    if (thread.isThreadLoading) {
+    if (thread.isThreadLoading && !suppressExistingThreadPrefetchUi) {
       document.title = `Loading... - ${t.pages.appName}`;
     } else {
       document.title = `${pageTitle} - ${t.pages.appName}`;
@@ -168,6 +180,7 @@ export default function ChatPage() {
     t.pages.appName,
     thread.values.title,
     thread.isThreadLoading,
+    suppressExistingThreadPrefetchUi,
   ]);
 
   const [autoSelectFirstArtifact, setAutoSelectFirstArtifact] = useState(true);
@@ -198,8 +211,9 @@ export default function ChatPage() {
 
   const [todoListCollapsed, setTodoListCollapsed] = useState(true);
 
-  const handleSubmit = useSubmitThread({
+  const submitThread = useSubmitThread({
     isNewThread,
+    createNewSession,
     threadId,
     thread,
     uploadTarget,
@@ -214,6 +228,13 @@ export default function ChatPage() {
       router.push(pathOfThread(threadId!));
     },
   });
+  const handleSubmit = useCallback(
+    (message: Parameters<typeof submitThread>[0]) => {
+      setHasSubmitted(true);
+      void submitThread(message);
+    },
+    [submitThread],
+  );
   const handleStop = useCallback(async () => {
     await thread.stop();
   }, [thread]);
@@ -268,8 +289,11 @@ export default function ChatPage() {
                   className={cn("size-full", !isNewThread && "pt-10")}
                   threadId={threadId}
                   thread={thread}
+                  suppressThreadLoading={suppressExistingThreadPrefetchUi}
                   messagesOverride={
-                    !thread.isLoading && finalState?.messages
+                    suppressExistingThreadPrefetchUi
+                      ? []
+                      : !thread.isLoading && finalState?.messages
                       ? (finalState.messages as Message[])
                       : undefined
                   }
@@ -306,7 +330,13 @@ export default function ChatPage() {
                     className={cn("bg-background/5 w-full -translate-y-4")}
                     isNewThread={isNewThread}
                     autoFocus={isNewThread}
-                    status={thread.isLoading ? "streaming" : "ready"}
+                    status={
+                      suppressExistingThreadPrefetchUi
+                        ? "ready"
+                        : thread.isLoading
+                          ? "streaming"
+                          : "ready"
+                    }
                     context={settings.context}
                     extraHeader={
                       isNewThread && <Welcome mode={settings.context.mode} />
diff --git a/frontend/src/components/workspace/messages/message-list.tsx b/frontend/src/components/workspace/messages/message-list.tsx
index 8f577fd5..db37d275 100644
--- a/frontend/src/components/workspace/messages/message-list.tsx
+++ b/frontend/src/components/workspace/messages/message-list.tsx
@@ -35,6 +35,7 @@ export function MessageList({
   threadId,
   thread,
   messagesOverride,
+  suppressThreadLoading = false,
   paddingBottom = 160,
 }: {
   className?: string;
@@ -42,13 +43,14 @@ export function MessageList({
   thread: UseStream<AgentThreadState>;
   /** When set (e.g. from onFinish), use instead of thread.messages so SSE end shows complete state. */
   messagesOverride?: Message[];
+  suppressThreadLoading?: boolean;
   paddingBottom?: number;
 }) {
   const { t } = useI18n();
   const rehypePlugins = useRehypeSplitWordsIntoSpans(thread.isLoading);
   const updateSubtask = useUpdateSubtask();
   const messages = messagesOverride ?? thread.messages;
-  if (thread.isThreadLoading) {
+  if (thread.isThreadLoading && !suppressThreadLoading) {
     return <MessageListSkeleton />;
   }
   return (
diff --git a/frontend/src/core/threads/hooks.ts b/frontend/src/core/threads/hooks.ts
index fab29800..b05a1341 100644
--- a/frontend/src/core/threads/hooks.ts
+++ b/frontend/src/core/threads/hooks.ts
@@ -21,10 +21,12 @@ import type {
 export function useThreadStream({
   threadId,
   isNewThread,
+  fetchStateHistory = true,
   onFinish,
 }: {
   isNewThread: boolean;
   threadId: string | null | undefined;
+  fetchStateHistory?: boolean;
   onFinish?: (state: AgentThreadState) => void;
 }) {
   const queryClient = useQueryClient();
@@ -34,7 +36,7 @@ export function useThreadStream({
     assistantId: "lead_agent",
     threadId: isNewThread ? undefined : threadId,
     reconnectOnMount: true,
-    fetchStateHistory: true,
+    fetchStateHistory,
     onCustomEvent(event: unknown) {
       console.info(event);
       if (
@@ -84,10 +86,12 @@ export function useSubmitThread({
   thread,
   threadContext,
   isNewThread,
+  createNewSession,
   uploadTarget,
   afterSubmit,
 }: {
   isNewThread: boolean;
+  createNewSession: boolean;
   threadId: string | null | undefined;
   thread: UseStream<AgentThreadState>;
   threadContext: Omit<AgentThreadContext, "thread_id">;
@@ -95,10 +99,21 @@ export function useSubmitThread({
   afterSubmit?: () => void;
 }) {
   const queryClient = useQueryClient();
+  const apiClient = getAPIClient();
   const callback = useCallback(
     async (message: PromptInputMessage) => {
       const text = message.text.trim();
 
+      // For "new session" semantics, ensure the target thread id starts fresh.
+      // If the same id already exists, delete it first and let submit recreate it.
+      if (createNewSession && threadId) {
+        try {
+          await apiClient.threads.delete(threadId);
+        } catch {
+          // Ignore delete errors (e.g. thread does not exist yet)
+        }
+      }
+
       // Upload files first if any
       if (message.files && message.files.length > 0) {
         try {
@@ -154,7 +169,7 @@ export function useSubmitThread({
           ] as HumanMessage[],
         },
         {
-          threadId: isNewThread ? threadId! : undefined,
+          threadId: createNewSession ? threadId! : undefined,
           streamSubgraphs: true,
           streamResumable: true,
           streamMode: ["values", "messages-tuple", "custom"],
@@ -170,7 +185,17 @@ export function useSubmitThread({
       void queryClient.invalidateQueries({ queryKey: ["threads", "search"] });
       afterSubmit?.();
     },
-    [thread, isNewThread, threadId, threadContext, uploadTarget, queryClient, afterSubmit],
+    [
+      thread,
+      isNewThread,
+      createNewSession,
+      threadId,
+      threadContext,
+      uploadTarget,
+      queryClient,
+      apiClient,
+      afterSubmit,
+    ],
   );
   return callback;
 }