From BotBuilder

This new iteration of Teams SDK has been rebuilt from the ground up. To ease the migration process, we've introduced a plugin @microsoft/teams.botbuilder that allows you to continue using BotBuilder components like ActivityHandler and CloudAdapter to receive, process and send activities within the new Teams SDK abstractions.

Why a Plugin?

The plugin exists to bridge BotBuilder and the new Teams SDK, letting developers keep their existing BotBuilder activity handlers while gradually moving to the new Teams SDK App handlers. It enables incremental migration and smooth adoption of new SDK features.