The S8 chip in the Apple Watch Series 8, Apple Watch Ultra, and second-generation Apple Watch SE features the same CPU as the S6 and S7 chips, according to identifier codes.
The CPU within Apple's S8 SiP carries the same T8301 identifier as the CPU in the S6 and S7 chips that debuted in the Apple Watch Series 6 and Apple Watch Series 7. This explains why Apple has only compared its S-series chips in recent years to the S5 chip or earlier.
It also means that the Apple Watch Series 6, Apple Watch Series 7, Apple Watch Series 8, Apple Watch Ultra, and second-generation Apple Watch SE all feature the exact same CPU. It is worth noting that Apple may have still iterated on other parts of the SiP to accommodate new components such as the Apple Watch Series 8's new accelerometer and gyroscope.
The S6, S7, and S8 chips all feature 32GB of storage and dual-core CPUs. When Apple debuted the S6 in the Apple Watch Series 6, the last time it made performance claims about its latest smartwatch lineup, it said that the chip allowed apps to launch 20 percent faster.
The S6, S7, and S8 are based on Apple's A13 Bionic chip from the iPhone 11 lineup and are manufactured using TSMC's 7nm process. Apple transitioned to TSMC's 5nm process starting with the A14 Bionic chip, and the iPhone 14 Pro's A16 Bionic is the first Apple chip to be fabricated with a 4nm process.
One explanation for Apple not advancing the CPU technology in its S-series chips is potential that advancements from using the cores in the A14 chip and TSMC's 5nm or 4nm processes would primarily yield performance improvements, which are no longer essential for the Apple Watch. Waiting for TSMC's 3nm process, which is set to enter mass production toward the end of this year, could yield more meaningful efficiency improvements – an area of much greater importance when it comes to the Apple Watch because it could help prolong battery life.
