The Elder Scrolls Online site has been updated with a news post to let players know that a new loyalty reward is incoming. With each new DLC, and grandfathered in for Orsinium and Thieves Guild, a reward of some sort will be earned either by purchasing the DLC from the Crown Store or by being an ESO Plus member and then entering the new area. The pet will automatically be sent.
Current Orsinium owners will receive an Echalette pet and Thieves Guild members will receive a Jackal. All future DLC will also feature a reward pet.
Read more on the Elder Scrolls Online site.