Very interesting interview with Hartley, seems there isn't much lap time difference between the different compounds. Wouldn't it be something if these tires are bogey tires? What I mean is it takes 2 steps to really see a difference, however, wear happens as you'd expect between two steps of tires. Maybe this means some interesting strategies are possible.
https://youtu.be/UaGRMrwIack?t=10m38s