diff --git a/apps/web/src/components/ThreadNotificationCoordinator.tsx b/apps/web/src/components/ThreadNotificationCoordinator.tsx
index a7134b481d131..10b7ecdc9d965 100644
--- a/apps/web/src/components/ThreadNotificationCoordinator.tsx
+++ b/apps/web/src/components/ThreadNotificationCoordinator.tsx
@@ -27,7 +27,7 @@ import {
   hasNotificationSound,
   playNotificationSound,
   setNotificationBadge,
-  threadNotificationTag,
+  notificationTag,
   unlockNotificationAudio,
 } from "../threadNotifications";
 import { resolveSidebarThreadStatus, type SidebarThreadStatus } from "./Sidebar.logic";
@@ -196,7 +196,7 @@ export function startThreadNotifications(
     try {
       const notification = new Notification(title, {
         body: thread.title,
-        tag: threadNotificationTag(environmentId, thread.id),
+        tag: notificationTag(`${environmentId}:${thread.id}`),
         silent: true,
         // Windows drops clicks after a toast moves into Notification Center.
         requireInteraction: kind === "completion" && isWindowsPlatform(navigator.platform),
diff --git a/apps/web/src/components/pullRequest/guide/PullRequestGuideRunCoordinator.test.ts b/apps/web/src/components/pullRequest/guide/PullRequestGuideRunCoordinator.test.ts
index a764c3c221d34..cd481e2212847 100644
--- a/apps/web/src/components/pullRequest/guide/PullRequestGuideRunCoordinator.test.ts
+++ b/apps/web/src/components/pullRequest/guide/PullRequestGuideRunCoordinator.test.ts
@@ -5,9 +5,14 @@ import {
   type PullRequestRef,
   type PullRequestReviewGuideResult,
 } from "@t3tools/contracts";
+import { DEFAULT_CLIENT_SETTINGS } from "@t3tools/contracts/settings";
 import { AsyncResult, Atom, AtomRegistry } from "effect/reactivity";
 import { expect, it, vi } from "vite-plus/test";
 
+import {
+  __resetClientSettingsPersistenceForTests,
+  __setClientSettingsForTests,
+} from "~/hooks/useSettings";
 import { guideRunKey, useGuideRunStore } from "./guideRunStore";
 import { startGuideRunNotifications } from "./PullRequestGuideRunCoordinator";
 
@@ -120,3 +125,51 @@ it("does not report the previous run's failure when a Running answer starts a wa
   expect(useGuideRunStore.getState().watches[key]).toBe(undefined);
   stop();
 });
+
+it("gives each finished guide's notification its own tag within the Windows toast limit", () => {
+  using _cleanup = {
+    [Symbol.dispose]: () => {
+      vi.unstubAllGlobals();
+      __resetClientSettingsPersistenceForTests();
+    },
+  };
+  const tags: string[] = [];
+  vi.stubGlobal("document", { visibilityState: "hidden", hasFocus: () => false });
+  vi.stubGlobal(
+    "Notification",
+    class {
+      static permission = "granted";
+      constructor(_title: string, options: NotificationOptions) {
+        tags.push(options.tag!);
+      }
+      addEventListener() {}
+    },
+  );
+  __setClientSettingsForTests({ ...DEFAULT_CLIENT_SETTINGS, notificationMode: "notifications" });
+  const registry = AtomRegistry.make();
+  const stop = startGuideRunNotifications(registry, { navigate: vi.fn() } as unknown as AnyRouter);
+  const uuidEnvironmentId = EnvironmentId.make("fd6fff30-f90b-4ee7-9812-4cf497791b90");
+  const written = {
+    guide: { generatedAt: "2026-10-01T00:00:00.000Z" },
+    run: null,
+  } as unknown as PullRequestReviewGuideResult;
+  for (const number of [1234, 1235]) {
+    registry.set(guideAtom(`${uuidEnvironmentId}:${number}`), AsyncResult.success(written));
+    useGuideRunStore.getState().watch({
+      environmentId: uuidEnvironmentId,
+      reference: {
+        projectId: ProjectId.make("a8395a98-a186-4fe7-9d4c-fb8ba63b7588"),
+        repository: "pingdotgg/t3code",
+        number,
+      },
+      title: null,
+      previousGuideAt: null,
+      previousFailedAt: null,
+      since: 0,
+    });
+  }
+  expect(tags).toHaveLength(2);
+  for (const tag of tags) expect(tag.length).toBeLessThanOrEqual(64);
+  expect(new Set(tags).size).toBe(2);
+  stop();
+});
diff --git a/apps/web/src/components/pullRequest/guide/PullRequestGuideRunCoordinator.tsx b/apps/web/src/components/pullRequest/guide/PullRequestGuideRunCoordinator.tsx
index f73755ed7d452..789ff522f2e3b 100644
--- a/apps/web/src/components/pullRequest/guide/PullRequestGuideRunCoordinator.tsx
+++ b/apps/web/src/components/pullRequest/guide/PullRequestGuideRunCoordinator.tsx
@@ -8,6 +8,7 @@ import { observedPullRequestTitle, pullRequestEnvironment } from "~/state/pullRe
 import {
   hasDesktopNotifications,
   hasNotificationSound,
+  notificationTag,
   playNotificationSound,
 } from "~/threadNotifications";
 
@@ -145,7 +146,11 @@ function watchGuideRun(
     )
       return;
     try {
-      const notification = new Notification(title, { body, tag: `guide:${runKey}`, silent: true });
+      const notification = new Notification(title, {
+        body,
+        tag: notificationTag(`guide:${runKey}`),
+        silent: true,
+      });
       notification.addEventListener("click", () => {
         notification.close();
         window.focus();
diff --git a/apps/web/src/threadNotifications.ts b/apps/web/src/threadNotifications.ts
index 8784f79baceef..697bef640847f 100644
--- a/apps/web/src/threadNotifications.ts
+++ b/apps/web/src/threadNotifications.ts
@@ -1,4 +1,3 @@
-import type { EnvironmentId, ThreadId } from "@t3tools/contracts";
 import type { ClientSettings } from "@t3tools/contracts/settings";
 
 import completionUrl from "./assets/notification-completion.mp3";
@@ -24,9 +23,8 @@ const TAG_HASH_OFFSET_BASIS = 0xcbf29ce484222325n;
 const TAG_HASH_PRIME = 0x100000001b3n;
 const TAG_HASH_MASK = 0xffffffffffffffffn;
 
-/** Windows drops toast notifications with the 73-character environment/thread tag. */
-export function threadNotificationTag(environmentId: EnvironmentId, threadId: ThreadId): string {
-  const key = `${environmentId}:${threadId}`;
+/** Windows drops toast notifications whose tag is longer than 64 characters. */
+export function notificationTag(key: string): string {
   let hash = TAG_HASH_OFFSET_BASIS;
   for (let index = 0; index < key.length; index += 1) {
     hash ^= BigInt(key.charCodeAt(index));