This is the first of a two-article sequence on ActivityPub groups. Part 1 covers ActivityStreams definitions, Mastodon API integration, and the client rendering logic. Part 2 will follow with a deep dive into the code behind populating the reply tree. Here we will briefly go through what a "group" Actor is in theory and how this maps to entities returned by APIs, what UX decisions were made to render posts published by a group and, when moving to the list to the detail screen, how conversations are displayed.