Some users of the Google Messages app now have the ability to respond to text messages with any emoji, rather than being limited to the app’s seven built-in options.
You can reply to a message with an emoji by long-pressing the message. This will bring up a pop-up menu with available options. Now there is a new element, clicking on which opens an additional menu with a wider selection of emoji options. The emoticons in this window are divided into categories. Recently used reactions are shown in the top row. Based on the available information, emoji reactions work for both RCS chats and SMS messages.
At the moment, extended reactions with emoji icons look like a limited test. Not all users have access to them. Google itself has not yet commented on this information in any way, so it remains only to speculate how wide testing is and when this feature will become publicly available.