diff --git a/scripts/ci/assemble-release.mjs b/scripts/ci/assemble-release.mjs
index 8f77dc1843..f342723092 100644
--- a/scripts/ci/assemble-release.mjs
+++ b/scripts/ci/assemble-release.mjs
@@ -3,7 +3,7 @@
 import { copyFile, lstat, mkdir, readFile, readdir, writeFile } from 'node:fs/promises'
 import path from 'node:path'
 import { pathToFileURL } from 'node:url'
-import { stringify } from 'yaml'
+import { Scalar, stringify } from 'yaml'
 
 import {
   compareFileNames,
@@ -433,7 +433,18 @@ function normalizeSingleArchitectureMetadata(packageEntry, version) {
 
 async function writeMetadata(outputDirectory, name, metadata) {
   const outputPath = path.join(outputDirectory, name)
-  await writeFile(outputPath, stringify(metadata), 'utf8')
+  // electron-updater parses updater yml with js-yaml, which turns an unquoted ISO
+  // timestamp into a Date object. The app's typed-IPC zod contract requires
+  // releaseDate to be a string, so force-quote it to guarantee a string round-trip
+  // under js-yaml. The `yaml` package used here does not quote ISO timestamps by
+  // default, unlike js-yaml's dump — this mismatch previously broke auto-update.
+  const serializable = { ...metadata }
+  if (typeof serializable.releaseDate === 'string') {
+    const quotedReleaseDate = new Scalar(serializable.releaseDate)
+    quotedReleaseDate.type = 'QUOTE_SINGLE'
+    serializable.releaseDate = quotedReleaseDate
+  }
+  await writeFile(outputPath, stringify(serializable), 'utf8')
   const inspected = await inspectRegularFile(outputPath, outputDirectory)
   return {
     name,
diff --git a/src/main/upgrade/index.ts b/src/main/upgrade/index.ts
index f45de02f25..6304fec569 100644
--- a/src/main/upgrade/index.ts
+++ b/src/main/upgrade/index.ts
@@ -78,10 +78,21 @@ const formatReleaseNotes = (notes?: string | ReleaseNoteItem[] | null): string =
 }
 
 const toVersionInfo = (info: UpdateInfo): VersionInfo => {
+  // electron-updater parses latest*.yml via js-yaml, which may turn an unquoted
+  // ISO releaseDate into a Date object. The publish pipeline now force-quotes
+  // releaseDate, but normalize defensively so any legacy yml artifact cannot
+  // leak a Date into the typed-IPC payload.
+  const rawReleaseDate = info.releaseDate as unknown
+  const releaseDate =
+    rawReleaseDate instanceof Date
+      ? rawReleaseDate.toISOString()
+      : typeof rawReleaseDate === 'string'
+        ? rawReleaseDate
+        : ''
   const releaseUrl = buildReleaseUrl(info.version)
   return {
     version: info.version,
-    releaseDate: info.releaseDate || '',
+    releaseDate,
     releaseNotes: formatReleaseNotes(info.releaseNotes),
     githubUrl: releaseUrl,
     downloadUrl: OFFICIAL_DOWNLOAD_URL
diff --git a/src/shared/contracts/events/upgrade.events.ts b/src/shared/contracts/events/upgrade.events.ts
index d1416ff9db..3e26e9e8bd 100644
--- a/src/shared/contracts/events/upgrade.events.ts
+++ b/src/shared/contracts/events/upgrade.events.ts
@@ -4,7 +4,12 @@ import { defineEventContract } from '../common'
 const UpgradeInfoSchema = z
   .object({
     version: z.string(),
-    releaseDate: z.string(),
+    // electron-updater may emit a Date when latest*.yml leaves releaseDate
+    // unquoted (js-yaml timestamp tag). Accept both and coerce to string so the
+    // publish pipeline and the client never disagree on shape.
+    releaseDate: z
+      .union([z.string(), z.date()])
+      .transform((value) => (value instanceof Date ? value.toISOString() : value)),
     releaseNotes: z.string(),
     githubUrl: z.string().optional(),
     downloadUrl: z.string().optional(),
diff --git a/test/main/upgrade/upgradeService.test.ts b/test/main/upgrade/upgradeService.test.ts
index dc8097fd0a..877e2ac06a 100644
--- a/test/main/upgrade/upgradeService.test.ts
+++ b/test/main/upgrade/upgradeService.test.ts
@@ -236,4 +236,35 @@ describe('UpgradeService', () => {
     expect((service as any)._status).toBe('available')
     expect((service as any)._versionInfo?.version).toBe('1.0.5')
   })
+
+  it('coerces a Date releaseDate from electron-updater into an ISO string for the IPC contract', () => {
+    // electron-updater parses latest*.yml via js-yaml, which turns an unquoted
+    // ISO releaseDate into a Date object. The service must normalize it before
+    // emitting so the typed-IPC zod contract never receives a Date.
+    appGetVersionMock.mockReturnValue('1.0.0')
+    const settings = {
+      getChannel: vi.fn(() => 'beta')
+    } as any
+
+    const service = new UpgradeService(
+      settings,
+      () => false,
+      requestUpdateInstallMock,
+      publishEventMock
+    )
+    const handler = autoUpdaterState.listeners.get('update-available')
+    expect(handler).toBeDefined()
+
+    const date = new Date('2026-07-25T11:28:19.451Z')
+    handler!({ version: '1.1.0-beta.6', releaseDate: date, releaseNotes: '' })
+
+    expect((service as any)._status).toBe('available')
+    const availableCall = publishEventMock.mock.calls.find(
+      (call) => call[0] === 'upgrade.status.changed' && call[1]?.status === 'available'
+    )
+    expect(availableCall).toBeDefined()
+    const info = availableCall![1].info
+    expect(typeof info.releaseDate).toBe('string')
+    expect(info.releaseDate).toBe('2026-07-25T11:28:19.451Z')
+  })
 })