question

No, there is no limit to the number of users that can be in a single chat room. There is also no limit to the number of chat rooms that any single user can be a member of.

Notes:

1. Chat rooms called out here are different than the chat that is provided in a meeting. As the limit for meeting attendees is 250, the max number of users in a meeting chat is also 250.
2. Currently, when there are more than 50 users @all and @present notifications are disabled. Also, on the Windows client, when there are more than 50 users we will not display the individual user's presence status in the @ mention user list.