What watchOS 27 Is and Why Compatibility Changed
watchOS 27 is the next major software update for Apple Watch, bringing new Siri AI capabilities, workout improvements, and interface refinements, but it also introduces one of the largest reductions in Apple Watch support to date by limiting installation to models with newer S9 or S10 chips and pairing them with recent iPhones running iOS 27. Apple has confirmed that watchOS 27 will run on Apple Watch Series 9 and later, Apple Watch Ultra 2 and later, and Apple Watch SE 3, provided they are paired with an iPhone 11 or later or an iPhone SE (2nd generation or later). This means owners of many popular watches that currently run watchOS 26 must decide whether to keep their hardware on older software or upgrade to a newer watch that will receive the update and its Siri AI features when watchOS 27 is released in the fall.
Full watchOS 27 Compatibility List—and the Series 9 U-turn
Apple’s final watchOS 27 compatibility list is short. Supported models are Apple Watch Series 9, Series 10, Series 11, Ultra 2, Ultra 3, and Apple Watch SE 3. All other models are excluded. This is notable because early information on Apple’s website appeared to omit the Series 9 entirely, despite it using the S9 chip and still being sold in refurbished form. Apple later told 9to5Mac that leaving the Series 9 off the list was a mistake, and Series 9 owners have been able to install the watchOS 27 developer beta. According to iClarified, “watchOS 27 is compatible with Apple Watch Series 9 and later, Apple Watch Ultra 2 and later, and Apple Watch SE 3.” For iPhone pairing, users need an iPhone 11 or later or iPhone SE (2nd generation or later), all running iOS 27, to install and use watchOS 27 on supported watches.
Which Apple Watches Lose Support—and Why It Matters
watchOS 27 drops support for every Apple Watch that lacks an S9 or S10 chip, including several models that ran watchOS 26. Affected devices include Apple Watch Series 6, Series 7, Series 8, the first-generation Apple Watch Ultra, and Apple Watch SE (2nd generation), as well as all earlier Series and SE models. These watches will remain on watchOS 26 or earlier and will not receive watchOS 27 when it ships later this year. TechRepublic notes that this is “one of the biggest device support cuts in the platform’s history,” because some of the excluded models were released as recently as 2022. Owners can keep using their watches for core functions and should still see basic maintenance and security updates, but they will miss new system features over time and may see app compatibility shrink as developers target watchOS 27 and later.
Siri AI, Apple Intelligence, and the Role of New Chips
The sharp line between watchOS 27 compatible models and older hardware appears tied to the new Siri AI and Apple Intelligence features. Every supported watch—Series 9, Series 10, Series 11, Ultra 2, Ultra 3, and SE 3—contains either Apple’s S9 or S10 chip, which include a stronger Neural Engine for machine-learning tasks. TechRadar and Macworld reports cited by TechRepublic suggest older models were dropped “presumably because those models can’t handle the new Siri AI.” iClarified also notes that Apple Intelligence features on watchOS 27 require Apple Watch Series 9 and later, Apple Watch Ultra 2 and later, or Apple Watch SE 3, paired with an Apple Intelligence‑enabled iPhone. Apple has not formally confirmed chip or AI requirements as the reason for the compatibility cut, but the hardware pattern suggests that running Siri AI at acceptable speed and on-device is a key design constraint.
Should You Upgrade or Stay on watchOS 26?
If you own an unsupported Apple Watch such as Series 8, Ultra 1, or SE 2, your choice comes down to feature access versus cost and lifespan. Staying on watchOS 26 keeps your current hardware working with core functions like notifications, fitness tracking, and existing apps, though future apps and features will increasingly target watchOS 27 compatible models. Upgrading to a Series 9, Series 10, Series 11, Ultra 2, Ultra 3, or SE 3 unlocks watchOS 27, Siri AI, and Apple Intelligence features when paired with a supported iPhone 11 or later or iPhone SE (2nd generation or later). For many, a reasonable path is to keep an unsupported watch for another cycle if it still meets daily needs, then plan a hardware upgrade when a key app, health feature, or Siri AI capability becomes important enough to justify switching to a watchOS 27 compatible model.
