So far they celebrated it with two shorts based on a really old style of animation which takes after the TAS batman and batman beyond:
http://io9.com/watch-the-new-batman-short-by-the-animated-series-creat-1562023661
http://io9.com/kevin-conroy-lends-his-voice-to-darwyn-cookes-batman-be-1565178912
http://io9.com/watch-the-new-batman-short-by-the-animated-series-creat-1562023661
http://io9.com/kevin-conroy-lends-his-voice-to-darwyn-cookes-batman-be-1565178912