That’s right, Spring 2017 will bring us a musical crossover with The Flash and Supergirl. It will last for two episodes. Now don’t get too nervous as this is completely separate from the crossover involving Arrow, The Flash, Supergirl, and Legends of Tomorrow. This little bit of information came from Executive Producer Greg Berlanti as he talked to Indiewire saying that,
Next week we’ll have to start talking about clearing music…I have a few ideas for tone and style in my head but we’re just starting to talk about what that can be. I do want to try to get an original piece of music written. As we make a deal on that we’ll probably make some announcements on the original songs.
There were talks about a request to Lin-Manuel Miranda, creator of Hamilton, to write an original song. Nothing has been set in stone as far as who they will have for the writer of the musical songs. Some of the cast members will be Grant Gustin, Melissa Benoist, Jesse L. Martin, and Jeremy Jordan. Both Grant and Melissa have appeared on Glee. Jesse has been seen on Rent. Then Jordan has been on Newsies, West Side Story, as well as Rock of Ages.
Now if you haven’t caught wind of the change in television stations as far as Supergirl has moved from CBS to The CW starting October 10th and The Flash will start its third season October 4th.