UPDATE (December 16th, 2019):

Sanaz Ahari, Communications Suite Lead for Google, has confirmed that RCS messaging is now available for all Android users in the United States. She made the announcement through a tweet and has asked users to update the Google Messages application. They will also need to install any Carrier Services update that many have been pending. Once you have updated both the things, you should be able to use RCS on any of the U.S. carriers.

Hi everyone! RCS is now available to all users in US as of Monday. Make sure to update both Messages and Carrier Services.

— Sanaz (@sanazahari) December 12, 2019

Original (November 15th, 2019)

After years of wait and consistent discussions with carriers, Google has decided to proceed with Rich Communication Services (RCS) rollout in the United States on its own. It will be released for all Android users in the US in the coming weeks with a full rollout expected to get completed before the end of this year.

RCS is a next-gen texting protocol that will succeed widely used SMS and MMS protocols. It is packed with various new features similar to instant messaging applications to fulfill the modern messaging needs of users. Some of the features include the ability to text over WiFi and mobile data, read receipts, typing indicator, creating and renaming texting groups, send/receive high-quality images and videos, and adding/removing people to groups.

These features and the new messaging protocol will be available through Google's Messages app meant for Android devices. It comes pre-installed on numerous devices, especially the ones running stock Android. Otherwise, one can also download and install the messaging app from the Google Play Store and set it as the default messaging application.

Once RCS becomes available for your particular device, the Messages app will automatically show you a prompt to "enable chat features". It goes without saying that both sender and recipient will need to have RCS enabled to make use of all the features. This is the reason the app will show "Chat message" instead of "Text message" in the message input field to show that RCS features can be used.

Google started rolling out RCS earlier this year when it made the protocol available for Android users in the United Kingdom, France, and Mexico. It had to proceed with the release itself even then as well. While it is loaded with many new features, it lacks one important feature and that is end-to-end encryption for conversations. It is a crucial security feature available on all major instant messaging apps and if you are concerned about privacy, you might want to refrain from using RCS for sharing sensitive information.