Microsoft is rolling out an upgraded rich federated experience for Teams to replace the previous plaintext 1:1 chat experience. When enabled, you’ll be able to send rich formatted text, emojis, and stickers to external Teams users in other Office 365 tenants and greatly increase the impact of your thoughts. The upgrade is rolling out now and should be complete worldwide by early December 2019.
https://office365itpros.com/2019/11/13/native-federated-chat-microsoft-teams/
