This doesn’t mean that they’re necessarily changing the continuity (several characters are returning, including those played by Mark Wahlberg and Josh Duhamel), as the earlier movies have shown that the Transformers are able to change their form if they need to. However, we don’t know how it will handle the alteration, as very little info has been released about the plot.
The poster does hint at robot dragons, big spaceships and, erm, a city, but not much more. It’s enough to set off plenty of speculation though. The film’s out summer 2017.