Are you asking for sol(t,Val{1}), the function for the derivative?
http://docs.juliadiffeq.org/latest/basics/solution.html#Interpolations-1
If you access that at one of the solution time points it will just give you the value of the derivative that it had stored in sol.k (and then the structure of k is different depending on the algorithm though… we can add a fake sol.du using getproperty overloading on v0.7 though if that’s useful?). But this is an interpolating function of the derivative as well.