A set of metrics are now available per Agent Assignment. A new event is written each time an agent is no longer assigned to a conversation: either because the assignment changed, or the conversation was no longer active. The assignment intervals provide information about each agent or bot who was assigned a conversation including metrics like the number of responses they sent, how long it was assigned, how long it took for a response to be sent after assignment, and the reason the assignment ended (closed by the agent, inactive by the system, transfer to another agent, etc.)
A CSV file of all of the agent assignments that ended during a timeframe can be downloaded from Reports > Historical Stats > Export Data > Agent Assignment. A new Conversation assignment ended event type is available in Reports > Insights when creating Funnels and Summary Cards as well.
More information can be found here