Jakusansei Million Arthur will be getting a televised anime series, there is no information regarding release dates, cast or staff. The tweet from director Mankyuu is vague, it only states the series will be getting televised, we don't know if the whole season is the only thing that will be broadcasted or if everything the show has done will be on screen (sequels, prequels, etc).
Jakusansei Million Arthur aired as an ONA, original net animation, which is web anime. A series that is directly released onto the internet and not broadcasted in television. However, just like Million Arthur's case, ONAs can be aired on television if they were released on the internet first.
The series aired from November 2015 to June 2018 and has a total of 60 episodes, Square Enix produced it and Gathering is the studio that animated it. Mankyuu directed it, Kisuke Koizumi was the sound director and Choboraunyopomi did the original character design. The series had a sequel that also aired as an ONA in April 2017. As soon as more information pops up on the televised series, we will let you know.