And, as is now tradition, the previous generation - in this case, the Apple Watch Series 8 - has been cast to the side to make way for the shiny new edition.
But for those weighing up which generation to choose (or Series 8 owners who want to feel better about sticking with their current model), it's important to understand everything that makes these watches tick.
After all, the Series 9 and Series 8 still have much more in common than they do differences.
Below, we've decided to pull together all the biggest changes - and a few of the key things that are still a core feature of both watches - to help you decide which you prefer.
Double tap gesture unlocks one-hand use
Apple's new 'double tap' gesture feature might not be the flashiest new change we've seen arrive to the smartwatch series, but it does sneakily have the potential to be one of the most useful in years.
This new feature essentially unlocks one-hand use, with Series 9 owners able to tap their thumb and index fingers together in order to control the primary option on the screen.
So, for example, if there's an incoming call and your non-watch hand isn't free to tap the screen, you can now instead double tap to answer it.
Apple also showed off examples of using double to remotely control the iPhone camera, as well as scroll through the watch face's Smart Stack.
Sadly, though, this isn't one for Series 8 owners. That's because double tap is powered by the all-new S9 SiP and 4-core Neural Engine, which processes data from the built-in accelerometer, gyroscope, and optical heart rate sensor in order to register the gesture.
The same design with hidden tweaks
Struggling to tell the difference between the Series 9 and Series 8? You should be, because these two smartwatches are essentially identical in their design.
Apple is sticking with the same 45mm and 41mm case size options of the Series 8 for the newer model, while the display size, band mechanism, button layout, and more are unchanged, too.
However, Apple has snuck in a couple of design improvements.
The Series 9 can reach a whopping 2,000 nits of brightness, which is double what you can manage on the Series 8.
For when you need that screen to get really dark, like in the cinema, it can now also go all the way down to 1 nit of brightness.
The price is right
We weren't sure whether Apple was going to hike up the price of the Series 9, but the new smartwatch will retail for the same price as the Series 8 did - $399/£399.
As ever, though, with the Series 8 now no longer on sale via Apple, it's very likely you'll find third-party retailers reducing the asking price of the watch in order to clear dead stock.
Ah, Siri - you remember Siri on the Apple Watch, right?
Well, Apple is using the Series 9 - thanks to that fancy new S9 SiP and Neural Engine - to make its smart assistant much more useful on the wrist.
For the first time, Siri requests will be processed on the watch itself, which means you'll no longer have to rely on a cellular connection or Wi-Fi for queries that don't require information from the internet.
So, starting a workout via Siri will now be much quicker, for example.
The assistant is also getting smarter, and will soon be able to fetch data from Apple Health. Arriving in an update later this year, you'll be able to ask the assistant how your Activity ring ios looking for the day, or whether you got a good sleep.
Again, though, like with the double tap gesture, this quicker and sharper version of Siri won't be landing on previous devices like the Series 8.
18-hour battery life forever
Those hoping that the immovable, never-ending promise of 18-hour battery life on Apple's Series devices would be improved for the Series 9 will no doubt be disappointed following its unveiling.
Apple is staying true to its perennial battery life estimate, which is the same as the Series 8 - and every Series device that came before it.
As we've noted over the last few generations, however, the number of hours of use you can expect has drastically improved.
We'd guess there may be some sneaky battery gains on account of that all-new S9 SiP, but, even if there aren't, the fact Apple delivers 'all-day' battery life while improving the speed and efficiency of actions on the watch isn't the worst thing to happen.
Finding your phone just got even easier
If the double tap gesture is the handiest new feature that's exclusive to the Series 9, the improvements made to Precision Finding appear to be a close runner-up.
With the S9 SiP including a new, second-gen Ultra Wideband (UWB) chip, the near-daily act of finding your lost phone has been made even better.
Providing you also have an iPhone 15, the Series 9 is now able to provide distance and direction cues, as well as visual, haptic, and audio guidance. And, you guessed it, this isn't one that will be available through Series 8 devices (or older).
This new and improved UWB chip is also deepening the integration between the Apple Watch and HomePod, kicking in playing suggestions and more when you're within 4m of the speaker. Pretty neat.
Leather is out
Apple spent a very solid chunk of time waxing over its 'Apple 2030' environmental goals during the unveiling of the Series 9 - and part of this drive includes phasing out leather watch bands.
Starting with the new generation, official Apple leather bands will no longer be sold. This also includes the long-standing Hermés collection of straps, which will now be made up of woven bands.
For those who really want a leather band with their new device, then, the Series 8 is the only choice.
Remember, though, you'll have to buy it from elsewhere, as Apple no longer sells the 2022 smartwatch.
Speaking of bands, the popular Sport Loop band has also been redesigned with more recycled materials, while Apple has also created a new 'FineWoven' material to help fill the leather void.
These FineWoven bands, Apple says, have a suede-like feel and will be available in the Modern Buckle and Magnetic Link styles.
Obviously, keep in mind you'll still pick up third-party options - like the ones in our best Apple Watch bands guide, for example.
Don't forget about watchOS 10
The Series 9 boasts a few enticing and exclusive tricks, but don't forget that the large majority of software features are existing ones or are new features landing watchOS 10 - an update the Series 8 will be getting.
You can read about everything new with watchOS 10 in our dedicated guide, but the highlights include a strong new emphasis on 'Smart Stack' widgets and a completely fresh look and feel to the operating system.
When added to the already-great GPS and heart rate tracking, health insights such as temperature monitoring, blood oxygen saturation readings, and Fall Detection, plus an App Store overflowing with great integrations, it can be easy to forget that the Series 8 is an exceedingly powerful watch in its own right.
Series 9 vs. Series 8: Which is better?
While we'll save our full verdict for after we've tested and reviewed the Apple Watch Series 9, it'll come as no surprise to note that the newer device is the better smartwatch out of the two on paper.
With that said, it also appears to represent a pretty minimal upgrade over the Series 8, which itself will now surely be the subject of price cuts and deals, as well.
We're interested to see exactly how much the double tap gesture transforms the day-to-day experience of the Apple Watch, but, other than this and perhaps the improved screen brightness, reasons to upgrade seem relatively slim.
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