diff --git a/apps/web/src/app/(v2)/chat/[thread_id]/page.tsx b/apps/web/src/app/(v2)/chat/[thread_id]/page.tsx
index 0d34bdbc..b8c7265b 100644
--- a/apps/web/src/app/(v2)/chat/[thread_id]/page.tsx
+++ b/apps/web/src/app/(v2)/chat/[thread_id]/page.tsx
@@ -2,6 +2,7 @@
 
 import { ThreadView } from "@/components/v2/thread-view";
 import { ThreadViewLoading } from "@/components/v2/thread-view-loading";
+import { ThreadErrorCard } from "@/components/v2/thread-error-card";
 import { useThreadMetadata } from "@/hooks/useThreadMetadata";
 import { useThreadsSWR } from "@/hooks/useThreadsSWR";
 import { useStream } from "@langchain/langgraph-sdk/react";
@@ -53,7 +54,7 @@ export default function ThreadPage({
     created_at: new Date().toISOString(),
   };
 
-  const { metadata: currentDisplayThread } = useThreadMetadata(
+  const { metadata: currentDisplayThread, statusError } = useThreadMetadata(
     dummyThread as any,
   );
 
@@ -61,6 +62,15 @@ export default function ThreadPage({
     router.push("/chat");
   };
 
+  if (statusError && "message" in statusError && "type" in statusError) {
+    return (
+      <ThreadErrorCard
+        error={statusError}
+        onGoBack={handleBackToHome}
+      />
+    );
+  }
+
   if (!thread || threadsLoading) {
     return <ThreadViewLoading onBackToHome={handleBackToHome} />;
   }
diff --git a/apps/web/src/components/v2/thread-error-card.tsx b/apps/web/src/components/v2/thread-error-card.tsx
new file mode 100644
index 00000000..2695293a
--- /dev/null
+++ b/apps/web/src/components/v2/thread-error-card.tsx
@@ -0,0 +1,101 @@
+import { Badge } from "@/components/ui/badge";
+import { Button } from "@/components/ui/button";
+import { Separator } from "@/components/ui/separator";
+import { cn } from "@/lib/utils";
+import { AlertCircle, ArrowLeft, Lock, Search } from "lucide-react";
+
+export interface ThreadStatusError {
+  message: string;
+  type: "not_found" | "unauthorized";
+}
+
+interface ThreadErrorCardProps {
+  error: ThreadStatusError;
+  onGoBack: () => void;
+}
+
+export function ThreadErrorCard({ error, onGoBack }: ThreadErrorCardProps) {
+  const getErrorIcon = () => {
+    switch (error.type) {
+      case "not_found":
+        return (
+          <Search className="h-4 w-4 text-amber-500 dark:text-amber-400" />
+        );
+      case "unauthorized":
+        return <Lock className="h-4 w-4 text-red-500 dark:text-red-400" />;
+      default:
+        return (
+          <AlertCircle className="h-4 w-4 text-red-500 dark:text-red-400" />
+        );
+    }
+  };
+
+  const getErrorTypeLabel = () => {
+    switch (error.type) {
+      case "not_found":
+        return "Not Found";
+      case "unauthorized":
+        return "Unauthorized";
+      default:
+        return "Error";
+    }
+  };
+
+  const getErrorTypeColor = () => {
+    switch (error.type) {
+      case "not_found":
+        return "border-amber-200 text-amber-600 dark:border-amber-800 dark:text-amber-400";
+      case "unauthorized":
+        return "border-red-200 text-red-600 dark:border-red-800 dark:text-red-400";
+      default:
+        return "border-red-200 text-red-600 dark:border-red-800 dark:text-red-400";
+    }
+  };
+
+  return (
+    <div className="bg-background fixed inset-0 flex items-center justify-center p-4">
+      <div className="bg-card w-full max-w-md rounded-lg border p-6 shadow-lg">
+        <div className="space-y-4">
+          <div className="flex items-center gap-2">
+            {getErrorIcon()}
+            <h4 className="text-sm font-semibold">Thread Error</h4>
+          </div>
+
+          <div className="space-y-3">
+            <div className="flex items-center justify-between">
+              <span className="text-muted-foreground text-xs font-medium">
+                Type
+              </span>
+              <Badge
+                variant="outline"
+                className={cn(getErrorTypeColor())}
+              >
+                {getErrorTypeLabel()}
+              </Badge>
+            </div>
+
+            <Separator />
+
+            <div className="space-y-2">
+              <span className="text-muted-foreground text-xs font-medium">
+                Message
+              </span>
+              <p className="text-sm font-medium">{error.message}</p>
+            </div>
+          </div>
+
+          <div className="pt-2">
+            <Button
+              onClick={onGoBack}
+              variant="outline"
+              className="flex w-full items-center gap-2"
+            >
+              <ArrowLeft className="h-4 w-4" />
+              Go Back
+            </Button>
+          </div>
+        </div>
+      </div>
+    </div>
+  );
+}
diff --git a/apps/web/src/hooks/useThreadMetadata.ts b/apps/web/src/hooks/useThreadMetadata.ts
index b6108f61..dd82c29a 100644
--- a/apps/web/src/hooks/useThreadMetadata.ts
+++ b/apps/web/src/hooks/useThreadMetadata.ts
@@ -5,6 +5,7 @@ import { useThreadStatus } from "./useThreadStatus";
 import { useMemo } from "react";
 import { getThreadTitle, computeThreadTitle } from "@/lib/thread";
 import { calculateLastActivity } from "@/lib/thread-utils";
+import { ThreadStatusError } from "@/lib/schemas/thread-status";
 
 /**
  * Hook that combines thread metadata with real-time status
@@ -12,7 +13,7 @@ import { calculateLastActivity } from "@/lib/thread-utils";
 export function useThreadMetadata(thread: Thread<ManagerGraphState>): {
   metadata: ThreadMetadata;
   isStatusLoading: boolean;
-  statusError: Error | null;
+  statusError: Error | ThreadStatusError | null;
 } {
   const {
     status,
diff --git a/apps/web/src/hooks/useThreadStatus.ts b/apps/web/src/hooks/useThreadStatus.ts
index d3a5283f..b17bf4da 100644
--- a/apps/web/src/hooks/useThreadStatus.ts
+++ b/apps/web/src/hooks/useThreadStatus.ts
@@ -56,7 +56,7 @@ export function useThreadStatus(
     status: data?.status || "idle",
     taskPlan: data?.taskPlan,
     isLoading,
-    error,
+    error: data?.error ?? error,
     mutate,
   };
 }
diff --git a/apps/web/src/lib/schemas/thread-status.ts b/apps/web/src/lib/schemas/thread-status.ts
index 4ac80e8f..2fdcaddd 100644
--- a/apps/web/src/lib/schemas/thread-status.ts
+++ b/apps/web/src/lib/schemas/thread-status.ts
@@ -33,6 +33,11 @@ export function mapLangGraphToUIStatus(status: ThreadStatus): ThreadUIStatus {
   }
 }
 
+export interface ThreadStatusError {
+  message: string;
+  type: "not_found" | "unauthorized";
+}
+
 export interface ThreadStatusData {
   graph:
     | typeof MANAGER_GRAPH_ID
@@ -42,4 +47,5 @@ export interface ThreadStatusData {
   threadId: string;
   status: ThreadUIStatus;
   taskPlan?: TaskPlan; // Task plan data when available from programmer sessions
+  error?: ThreadStatusError;
 }
diff --git a/apps/web/src/services/thread-status.service.ts b/apps/web/src/services/thread-status.service.ts
index 9b562dd0..4b131f5e 100644
--- a/apps/web/src/services/thread-status.service.ts
+++ b/apps/web/src/services/thread-status.service.ts
@@ -11,6 +11,42 @@ import { PlannerGraphState } from "@open-swe/shared/open-swe/planner/types";
 import { getActivePlanItems } from "@open-swe/shared/open-swe/tasks";
 import { SessionCache, SessionCacheData } from "@/hooks/useThreadsStatus";
 
+function getErrorFields(error: unknown): {
+  message: string;
+  type: "not_found" | "unauthorized";
+} {
+  if (
+    !error ||
+    typeof error !== "object" ||
+    !("message" in error) ||
+    !("status" in error)
+  ) {
+    return {
+      message: "Unknown error",
+      type: "unauthorized",
+    };
+  }
+
+  if (error.status === 404) {
+    return {
+      message: "Thread not found",
+      type: "not_found",
+    };
+  }
+
+  if (error.status === 401) {
+    return {
+      message: "Unauthorized",
+      type: "unauthorized",
+    };
+  }
+
+  return {
+    message: "Unknown error",
+    type: "unauthorized",
+  };
+}
+
 interface StatusResult {
   graph: "manager" | "planner" | "programmer";
   runId: string;
@@ -134,6 +170,7 @@ export async function fetchThreadStatus(
       sessionCache,
     );
   } catch (error) {
+    const errorFields = getErrorFields(error);
     console.error(`Error fetching thread status for ${threadId}:`, error);
 
     const graph = lastPollingState?.graph || "manager";
@@ -145,6 +182,7 @@ export async function fetchThreadStatus(
       runId,
       threadId: errorThreadId,
       status: "error",
+      error: errorFields,
     };
   }
 }