watchOS 26 アップグレード：対応 Apple Watch、iPhone バックアップ、更新と初期設定
watchOS 26 の公式互換・バックアップ・更新手順。
watchOS 26 を入れる前に Apple の互換リストを確認し、iPhone で iCloud バックアップ（ペアリングした Apple Watch データ含む）を取ってから Watch App または本体のソフトウェアアップデートでインストールしてください。
Apple 公式の watchOS 26 アップグレード：互換、バックアップ、更新、初期設定。
watchOS 26 (Apple)
Liquid Glass
Smart Stack, Control Center, Photos face (Apple watchOS 26 notes).
Health
Hypertension notifications, sleep score, Vitals where supported.
Workout Buddy
Apple Intelligence voice motivation on supported pairs.
Messages
Live Translation and Smart Stack hints where available.
Compatibility
Apple lists Series 11, SE 3, and Ultra 3 for watchOS 26 or later with iPhone 11+ and iOS 26+. Other models show the newest watchOS Software Update allows.
Backup on iPhone
- 1
Update iPhone
- 2
Pairing + sync
Watch app → My Watch on Wi‑Fi.
- 3
iCloud Backup
Settings → iCloud → iCloud Backup → Back Up Now (includes watch data).
- 4
Charge
Watch ≥50% per Apple; iPhone on Wi‑Fi nearby.
Install watchOS 26
- 1
Update Tonight
Notification on watch, confirm on iPhone, charge overnight.
- 2
Watch app
My Watch → General → Software Update → Download; keep on charger.
- 3
On watch
Settings → General → Software Update on Wi‑Fi.
After install
- 1
Smart Stack / Control Center
- 2
Health permissions
- 3
Workout Buddy
- 4
Automatic Updates
Watch app → Software Update.
# Official starting points
https://support.apple.com/en-us/123002
https://support.apple.com/en-us/108926
https://support.apple.com/en-us/118490
https://support.apple.com/guide/watch/update-applewatch-software-apd105341ac3/watchos
https://support.apple.com/guide/watch/welcome/watchos
https://www.apple.com/newsroom/2025/09/new-versions-of-apples-software-platforms-are-available-today/Still stuck?
Software Update never offers watchOS 26?
Apple says incompatible watches only show the newest watchOS they support. Confirm your model on Apple's compatibility table and in Software Update on the watch or in the Watch app.
Must I update iPhone first?
Apple requires your iPhone on the latest compatible iOS before watchOS updates. For watchOS 26 on Series 11, SE 3, and Ultra 3, Apple lists iPhone 11 or later with iOS 26 or later.
Does iCloud backup include my watch?
When paired, Apple Watch data is included in your iPhone backup. Run an iCloud backup on the iPhone before major updates per Apple's iPhone backup guidance.
Update stuck on the progress wheel?
Keep the watch on its charger, leave the iPhone nearby, and do not restart either device during install. Apple Support suggests restarting both and deleting a partial update under Watch app → General → Storage if needed.