Anonymous redditor seems to confirm Google's Project Hera with Gmail screenshot

The post was done with a throwaway account, so it's impossible to follow-up, but the post specifically says that "Project Hera is real, but AP leak is not." The post doesn't mention whether or not the theory about the HTML5 functionality integration was accurate, but it does say that the mock-ups that were posted were not accurate. As "proof", the redditor posted a picture of a development version of a Gmail redesign in the works. 

We had seen a leak of a Gmail redesign recently as well, and the two images don't exactly match up too much. The solid color bar at the top matches (though it is a different color), and that also matches a Google Calendar redesign that we saw earlier today. Otherwise though, the leak looks basically the same as Gmail's current UI, except for that top bar. The post does include the caveat that the image may be outdated though. 

Of course, because this was posted with a throwaway account, we have no idea if this information is accurate or not, so for all we know, AP might have it right. Time will have to tell. 

source: reddit via BGR