As spotted by MacRumors, the system requirements for watchOS 27 are pretty steep:
Apple today confirmed that watchOS 27 will not support the Apple Watch Series 9, Apple Watch Ultra (first generation), or Apple Watch SE (second generation), effectively drawing a line at devices equipped with the S9 or S10 chip.
The only Apple Watch models compatible with watchOS 27 are the Apple Watch Series 10, Series 11, Ultra 2, Ultra 3, and SE 3. Despite the fact that the Apple Watch Ultra 2 contains the S9 chip, the Series 9 which contains the same chip will no longer be supported.
Of note, a bunch of iPads also got the axe, while iOS 27 will support the same devices iOS 26 did, reaching back further than ever before, to the iPhone 11.
Update: It looks like the Series 9 is supported.
Based on my analytics, it looks like watchOS 27 will be available for download on around 40% of my Pedometer++ users’ watches. Which feels pretty small. That will certainly be boosted by whatever new devices get announced this fall, but it feels like I’ll be supporting watchOS 26 for a very long time, as a huge number of devices will be staying there.