The project is being directed by
Noam Murro (2008's Smart People) and the script was written by Kurt Johnstad and Zack Snyder, who co-wrote the first 300 with Michael Gordon.
https://www.imdb.com/title/tt1253863/
One of the great iconic performances of recent times,
Gerard Butler will not reprise his role as King Leonidas in the 300 follow-up.
He said, "I'm not doing it. I wish them the best, but it didn't work out. It wasn't really my thing."
I think the primary reason he turned it down is that the role was probably a cameo or a very short role. Butler had said in the past that he would be prepared to put himself through the absolute brutal training regime required for the role only if the role was substantial enough. Makes sense to ditch it if you have to go through all that hard work for a 5 minute role or something.