Teams Live Events vs. Yammer Live Events

Live Events in Yammer is only for internal use, Live Events in Teams can be used for public events that allows external viewers (non-authenticated anonymous users). LE Yammer uses Microsoft Stream and LE Teams uses Stream for internal broadcasts and Azure Media Services for public events.

With Yammer you use an third-party application to produce, with Teams you can use a third-party applications (internal events only) or you can use the Teams client to produce your event.

With yammer you can have an ongoing discussion/conversation about the stream, with Teams you only have the Q&A feature.