Google Chat APIs now generally available to all Workspace developers- Google Developers Blog

The Google Chat API, previously in Developer Preview for creating spaces and adding members, is now generally available to all Workspace developers. This includes APIs for managing messages, reactions, and attachments. Additionally, a new Developer Preview feature allows Chat apps to import user data (messages, attachments, reactions, memberships) into 'import mode' spaces, which preserve historical timestamps and suppress notifications during import.