But what happens when you send a message with one of these options to a friend not rocking iOS 10 or macOS Sierra? Here's how the new messages show up on older iPhone, iPads, and Macs.
Bubble and screen effects
When it comes to making message bubbles pop out on the screen or fill your window with balloons, older versions of iOS and OS X don't quite know what's going on. But like any good piece of accessibility software, they're happy to describe it to you: Send a message with the Slam effect to someone on an older device, and they'll see your original message, followed by:
(sent with Slam Effect)
All the little bubbles have the "sent with [effect] Effect" wording, while the full-screen alerts just describe the screen contents. For instance, if you sent someone a message with the shooting star effect, your recipient would get the original message, followed by:
(sent with Shooting Star)
In theory, macOS Sierra should get all these effects, but as of the public beta only Invisible Ink is rendering properly, so you may see some commented bubble effects on that platform, too.
Tapbacks and big emoji
When you double-tap or press-and-hold on a message in iOS 10, you can send a "tapback" — Apple's version of a Facebook or Slack reaction. On the public betas, those render as little icons in the upper right corner of your pal's message bubbles, but older versions of the software don't have that icon set to play with.
Instead, if you send a "Ha ha" tapback on your friend's picture of Pikachu, he'll see:
Laughed at an image
It's a little strange, but as my colleague Lory Gil put it: "At least we know how you feel, even if we can't see it."
On the emoji side, iOS 10 and macOS Sierra can display huge icons if you're using three or fewer of them; older versions of Apple's operating systems will simply display those emoji at regular size.
Stickers, gifs, and URLs
One of Messages' big improvements in iOS 10 and macOS Sierra is the introduction of Sticker packs and gifs: Images that you can send as is, or "stick" to the sides of your friends' messages in reaction.
Send those stickers to a buddy on iOS 9 or OS X El Capitan, however, and you'll get static images. If you've attached them to a specific message bubble, that won't display — you'll just see the stickers load one after the other.
The other big Messages change — contextual URLs, which display previews of web pages or services like Apple Music — just show up as normal old web URLs on older machines.
Handwriting and Digital Touch
Last but not least, we have Apple's watchOS-turned-iOS-and-macOS features: Handwriting and Digital Touch. With the company's Digital Touch drawing board, you can annotate over photos or video, draw a sketch, send a series of taps, or send a kiss. And tilt your device horizontally, and you'll get a sketch pad where you can handwrite out your message, to be delivered in real time.
On older devices, these features mostly work, though without the animations present on iOS 10 and macOS Sierra. Your sketch and handwriting samples will send as fully-realized masterpieces rather than displaying line-by-line, your kiss displays as a blank black screen, and any tap sequence you send will display all the taps on the screen together — one big mass of overlapping circles.