After signing with adidas the word on the street is that Sumner is going to be taken care of by Justin Rinaldi.
Definitely makes sense, Rinaldi has arguably the best pure 800m crew in the business, having Joseph Deng, Peter Bol, Brad Mathas, Guy Learmonth active in his stable as well as coaching (coached???) 1.44 performers Jeff Riseley and Alex Rowe.
As we know JR is active on the boards so all good stuff, best of luck to Sumner in the upcoming 800 final.