The official site for the Seven Deadly Sins announced that there is going to be a new anime special that will run for 4 weeks starting this August. Nakaba Suzuki the writer for the Seven Deadly Sins is creating a whole new story for the special. The staff has revealed a key visual which will be below and Aniplex is streaming a short clip previewing the work in progress.
Partial Rough Translation:
Meliodis: Ban, did you hear we’re coming back to TV!
Ban: That sounds like fun.