Google's Messages app — the standard text-messaging app on Android — will become "Chat," according to The Verge. With that change comes the ability to send prettier photos, longer messages, and lots of other "rich" interactivity.
As it is now, Android uses standard SMS text messaging, which is limited to a certain number of characters, and multimedia (photos, video) is highly compressed (it looks bad).
With Google Chat, Android text messaging will become much more like Apple's beloved iMessage.
All these new features in Android text messaging are due to the adoption of RCS, or rich communications services, a new standard for text messaging. In short, the RCS standard operates on data networks (like Apple's iMessage) instead of phone networks (like traditional SMS text messaging).
Moreover, Google has a bunch of big phone makers signed on to RCS — from Samsung to LG to Huawei and HTC.
If someone on a Pixel sends a message to a Samsung Galaxy S9, for instance, they can share "RCS" messages — theoretically, anyway, as Samsung is one of the companies that's signed on. And if you try sending a message and the other person's phone doesn't support RCS? They'll receive it as a standard SMS message (similarly to iMessages showing up for Android users as SMS messages).
For now, Apple isn't signed on to support RCS messaging: No, the iPhone will not support these messages. At least not for now. Also of note: RCS messages aren't as secure as iMessages; there's no "end to end" encryption, which prevents communications from being intercepted by third parties.
The changes to Android text messaging are coming in the next year, according to The Verge.