According to Anime News Network, Aniplex announced the upcoming adaptation of “Mahouka: Reminiscence Arc” in February 2021. This announcement came in celebration of the franchise’s 10th anniversary, during which Aniplex released an official teaser trailer for the upcoming anime. At the time, Aniplex did not reveal an official release date.
That changed, however, when Aniplex debuted the first commercial for its adaptation of the “Reminiscence Arc” following the finale of the franchise’s spinoff anime, “The Honor Student at Magic High School” (via a separate article from ANN). The commercial, which was also shared on the official “Mahouka” Twitter, revealed that the “Reminiscence Arc” would begin broadcasting in winter 2021.
Despite this, Aniplex did not reveal when the anime would be available anywhere but Japan’s television market. As with most anime, it is likely to find its way onto a streaming service such as Funimation or Crunchyroll. When this might happen, however, remains a mystery.