Because series 11 returns to a massive story arc that started in series 3, Big Finish made this 10 minute animated special.
It brings together events from the past in order to set up their resolution in series 11 and also serves as an introduction to the range for newcomers by quickly telling the story so far.
Therefore, whilst not an audio per se, the tie in is too important to be left out of the audio range.
It can be seen on Youtube.