Sega has released a debut trailer (all CG) for the new Sonic the Hedgehog title that has been teased for a while now. It may be Sonic's 25th birthday this year, but the new game won't be out until holiday 2017.
The short trailer talks of dark times and we see some Eggman-esque machinery doing evil things (presumably). Modern Sonic comes speeding forward, but as big boulder comes his way he is saved by classic Sonic.
So presumably both will feature in the game, and maybe this is a continuation of Sonic Generations or perhaps just some of the elements in that game.
Sega also confirmed that the game is coming to the new Nintendo NX console, PC, PS4, and Xbox One.