Microsoft will increase the participant limit from 300 to 1000 participants. 1000 participants will be able to join the interactive Teams meeting and the meeting chat, what also will support 1000 chat participants. If more users tries to join they will be joined as view-only participants.
The rollout will start mid-March and be completed in mid-April. There is no extra license required for this.
With large meetings like this it is important that the meeting organizer prepares the meeting with only a few presenters. Recommended to not allow attendees to unmute, instead they can raise their hand when they want to speak and a presenter can promote them to presenter so they can unmute.