If you are wearing an Apple Watch Series 6 or older, watchOS 27 will not install on it on Monday, September 14. Apple’s replacement lineup is three watches: SE 3 from $249, Series 12 from $399 and Ultra 4 from $799.
Apple’s watchOS 27 compatibility footnote lists SE 3, Series 9, Series 10, Series 11, Series 12, Ultra 2, Ultra 3 and Ultra 4. Series 6, Series 7, Series 8, the second-generation SE and the first Apple Watch Ultra are not on it.
Key facts
| Item | Apple Watch SE 3 | Apple Watch Series 12 | Apple Watch Ultra 4 |
|---|---|---|---|
| Starting price | From $249 | From $399 | From $799 |
| Case sizes | 40mm, 44mm | 42mm, 46mm | 49mm |
| Chip | S10 | S11 | S11 |
| Peak brightness | Up to 1000 nits | Up to 2000 nits | Up to 3000 nits |
| Battery, normal use | Up to 18 hours | Up to 24 hours | Up to 50 hours |
| Water resistance | 50 m | 50 m | 100 m |
| Electrical heart sensor | Not listed | Yes | Yes |
Why the update stops where it does
Apple’s September 2025 releases said watchOS 26 would be available for Apple Watch Series 6 or later and Apple Watch SE second generation or later. Series 6 was the oldest model on that list, and watchOS 27 moves the floor up to Series 9.
Don’t miss the best of The Mac Observer
Set us as a preferred source and our Apple reporting ranks higher in your Google Search results and Discover feed — one tap, no account changes.
Your watch keeps working. It keeps telling the time, tracking workouts and taking calls. What it stops receiving is the yearly feature release, and the new Series 12 health features depend on hardware it never had.
There is one requirement worth checking before you spend anything: watchOS 27 needs an iPhone 11 or later, or an iPhone SE second generation or later, running iOS 27.
Five years of hardware change, using Series 7 as the marker
Apple’s comparison tool now covers only the current watches and last year’s models, so there is no Apple-published Series 6 against Series 12 table. The nearest documented reference point is Series 7 from 2021, whose tech specs are still online.
| Spec | Series 7 (2021) | SE 3 (2025) | Series 12 (2026) |
|---|---|---|---|
| Chip | S7 | S10 | S11 |
| Peak brightness | 1000 nits | 1000 nits | 2000 nits |
| Battery | Up to 18 hours | Up to 18 hours | Up to 24 hours |
| Temperature sensor | No | Yes | Yes |
| Depth gauge | No | No | Yes, to 6 m |
| Case materials | Aluminum, stainless steel, titanium | Aluminum with Ion-X glass | Aluminum with Ceramic Shield 2, titanium, ceramic |
| Launch price | $399 | $249 | From $399 |
The pattern is clear enough. Battery life and brightness moved on the Series line and stayed flat on the SE line, while sensors arrived in stages: temperature in 2022 on Series 8, and the new heart sensing system this year.
SE 3 at $249 or Series 12 at $399
This is the decision most owners of an old watch actually face, and one detail settles it more often than any other. If your Series 6 or Series 7 had the ECG app and Blood Oxygen, SE 3 does not: Apple’s SE 3 tech specs list neither an electrical heart sensor nor a Blood Oxygen sensor.
Moving to SE 3 is therefore a step sideways on sensors and a step forward on chip and software support. Moving to Series 12 keeps everything you had and adds heart rate readings every five seconds, HRV every five minutes, a Readiness score and a 2000-nit display.
Series 12 also charges faster than anything from 2021: 80 percent in about 30 minutes, and 15 minutes on the charger for up to 12 hours of normal use.
When $799 is the right answer instead
Ultra 4 doubles the battery rating to 50 hours, adds satellite messaging and Emergency SOS, a 100 m water rating with a depth gauge to 40 m, dual-frequency GPS and a 3000-nit display, all in a 49mm titanium case that weighs 63 g.
If your old watch spent its life on a desk and a treadmill, none of that is worth $550. If it spent weekends out of phone range, it is the only one of the three that answers the problem.
What Apple has not said
Apple publishes starting prices only. There is no published price list for SE 3 in 44mm, for cellular models, or for the Series 12 titanium and ceramic cases, and band prices are not published either.
Apple’s trade-in page also shows no dollar figure per watch model. It asks condition questions and produces an estimate, so any per-model number you see is a value recorded elsewhere, not an Apple quote. Apple has not said how long Series 9 and Series 10 will keep getting updates either.
watchOS 27 lands as a free update on Monday, September 14 for the eight supported watches. Series 12 and Ultra 4 reach stores on Friday, September 18, alongside the rest of Apple’s September announcements.
