This morning, Bethesda tweeted a link to this page on their official website. Similar pages have popped up over the past few years and have turned out to be hoaxes. But this one, hosted by Bethesda themselves and promoted on their official social media accounts is very definitely the real deal.
The clock on the page is counting down to 10am EST on June 3rd (aka, tomorrow). There doesn’t seem to be anything cool going on the page source (as there sometimes is on these teaser pages) aside from a very Fallout themed error message. Bethesda has changed the header image of their official twitter to the same “Please Stand By” image, edited to have a “Rating Pending” ESRB sticker on it, confirming that this coming announcement is indeed a new game.