A recent AARP study uses 2017 data from IBM Marketscan to answer this question. Their data focuses on commercial and Medicare databases. They find that generic prices in 2017 fell by 9.3%. On the other hand, the price of specialty drug prices rose by 7%. The average annual cost of specialty drugs in the US is now $78,871.
Taking both trends into account, the gap between brand and generic drugs is rising. Whereas in 2013 brands were 570% of the cost of generics, in 2017 they are now 1860% of the cost of generics. This has lead some to believe that in fact generic prices are too low. Nevertheless, the high price of specialty drugs is putting pressure on payer budgets.