diff --git a/.changeset/tidy-moons-repeat.md b/.changeset/tidy-moons-repeat.md
new file mode 100644
index 00000000000..4c2511d0d28
--- /dev/null
+++ b/.changeset/tidy-moons-repeat.md
@@ -0,0 +1,5 @@
+---
+'@tanstack/angular-query-experimental': patch
+---
+
+Register the Angular pending task when `mutate` is called, so `whenStable()` no longer resolves while the mutation is still running
diff --git a/packages/angular-query-experimental/src/__tests__/pending-tasks.test.ts b/packages/angular-query-experimental/src/__tests__/pending-tasks.test.ts
index c5a1f58d81f..ec71e9840f0 100644
--- a/packages/angular-query-experimental/src/__tests__/pending-tasks.test.ts
+++ b/packages/angular-query-experimental/src/__tests__/pending-tasks.test.ts
@@ -155,6 +155,31 @@ describe('PendingTasks Integration', () => {
     })
   })
 
+  // The observer reports a running mutation through a batched notification that
+  // only lands in a later task. This test uses real timers because it asserts
+  // on what `whenStable()` does before that notification arrives.
+  describe('Task registration timing', () => {
+    it('should let whenStable wait for a mutation that was just triggered', async () => {
+      vi.useRealTimers()
+
+      const app = TestBed.inject(ApplicationRef)
+
+      const mutation = TestBed.runInInjectionContext(() =>
+        injectMutation(() => ({
+          mutationFn: (value: string) => sleep(5).then(() => value),
+        })),
+      )
+
+      TestBed.tick()
+      mutation.mutate('mutated')
+
+      await app.whenStable()
+
+      expect(mutation.status()).toBe('success')
+      expect(mutation.data()).toBe('mutated')
+    })
+  })
+
   describe('Race Conditions', () => {
     it('should handle query that completes during initial subscription', async () => {
       const key = queryKey()
diff --git a/packages/angular-query-experimental/src/inject-mutation.ts b/packages/angular-query-experimental/src/inject-mutation.ts
index 7eb605047f3..94ede348d56 100644
--- a/packages/angular-query-experimental/src/inject-mutation.ts
+++ b/packages/angular-query-experimental/src/inject-mutation.ts
@@ -87,7 +87,15 @@ export function injectMutation<
   >(() => {
     const observer = observerSignal()
     return (variables, mutateOptions) => {
-      observer.mutate(variables, mutateOptions).catch(noop)
+      // `mutate` is fire and forget, so nothing else keeps the application
+      // busy while the mutation runs. The observer reports the pending state
+      // in a batched notification that only arrives in a later task, so hold a
+      // pending task from the moment the mutation starts instead.
+      const releasePendingTask = pendingTasks.add()
+      observer
+        .mutate(variables, mutateOptions)
+        .catch(noop)
+        .finally(releasePendingTask)
     }
   })