The Apple Watch Series 9 and Ultra 2 were announced during Apple's "Wonderlust" event on September 12, 2023. Both of these Apple Watch models have the new Apple S9 system-in-package utilizing the energy-efficient Sawtooth cores from the A16 Bionic with a faster GPU and a four-core Neural Engine, improved power efficiency, and a second-generation Ultrawide Band chip (shared with iPhone 15) with improved precision and a farther range. Their displays have a higher maximum brightness than their predecessors. Both Apple Watch Series 9 and Apple Watch Ultra 2 ship with watchOS 10; they support on-device Siri and a new "double tap" gesture using the index finger and thumb.
Prior to the announcement of the watchOS 26 at Apple's WWDC 2025, a new feature "wrist flick" gesture (using the wrist to quickly turn over and back to dismiss the incoming notification) will be available on the Apple Watch Series 9 and Apple Watch Ultra 2 alongside the Apple Watch Series 10.
For legal reasons, blood oxygen monitoring was not available on Apple Watch Series 9 and Ultra 2 models sold in the United States after January 18, 2024.
Following a ruling by the International Trade Commission on a lawsuit regarding the blood oxygen monitoring feature, Apple temporarily stopped selling Apple Watch Series 9 and Ultra 2 on December 21, 2023, ahead of an import ban going into effect December 26, 2023. At the time, 9to5Mac reported, "Apple says that the ITC’s ban only impacts sales of the Apple Watch Series 9 and Apple Watch Ultra 2 because those devices offer blood oxygen monitoring capabilities." A US Federal Appeals Court paused the import ban pending a US Customs and Border Protection ruling on whether Apple's changes would be enough to avoid the patent dispute, and Apple resumed sales on December 27, 2023.
On August 14, 2025, Apple reintroduced blood oxygen monitoring for affected Series 9, Series 10, and Ultra 2 Apple Watches with the iOS 18.6.1 and watchOS 11.6.1 software updates. To circumvent patent disputes, the redesigned app no longer analyzes blood oxygen data through the on-device app. Raw data is collected by the Apple Watch, then "measured and calculated on the paired iPhone."