Teams will allow up to 1000 participants to join regular Teams meeting.
The meeting organizer must have one of the following license to create an 1000 person meeting:
Microsoft 365 E3/E5
Microsoft 365 A3/A5
Microsoft 365 Government G3/G5
Meanwhile, there are some limitations for large meetings:
One is breakout rooms are currently not supported in the meeting which contains more than 300 people.
Another is the meeting chat is available to the first 1,000 people who are invited to a meeting. If more than 1,000 people are invited to a meeting, the meeting chat will not be available to the people who were added to the meeting invite after the 1,000th person was added - regardless of whether the first 1,000 people invited actually attend the meeting.
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