Sonic 2017's Official Title is Sonic Forces, Sonic Mania Delayed to Summer

SEGA announced a pair of updates regarding the two Sonic the Hedgehog games the publisher has in development.
The first gameplay of modern Sonic in Sonic Forces is coming soon.

Sonic 2017's Official Title is Sonic Forces, Sonic Mania Delayed to Summer

Sonic Mania Delayed; Project Sonic 2017 Gets A Name - GameSpot

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Sonic 2017's Official Title is Sonic Forces, Sonic Mania Delayed to Summer - IGN

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Sonic Mania' delayed, 'Project Sonic 2017' is called 'Sonic Forces