You can now chat with meeting attendees directly from Google Calendar. Within the Calendar event on web or mobile, you will see a Chat icon next to the guest list — simply select this icon to create a group chat containing all event participants. This makes it simple to chat with guests before, during, or after any meeting. The email and chat options are side by side on a calendar event. This can help you quickly choose whichever form of communication you prefer, and start conversations with just a few taps.

Note: Chat will only be available to participants within the domain, external attendees will not be included in the chat group. 

Availability
The feature will begin rolling out to accounts last week, but may take up to 15 days to reach all accounts. Please visit the Google Workspace Learning Center to learn more about Chatting with attendees.