The confirmation came in a rather odd way: a fan via Twitter said their boyfriend had a dream about Bethesda announcing the game will not be out or have any news relayed about it until 2021, meaning he could relax, presumably from the tension of not knowing when an announcement might emerge. Bethesda Vice-President Pete Hines advised the fan that their boyfriend was "very smart."
Starfield is Bethesda's next big open-world CRPG, their effective follow-up to 2015's Fallout 4 and 2011's Skyrim. It's their first new, original IP since the first Elder Scrolls game, Arena, was published all the way back in 1994. Bethesda have revealed very little about the game aside from the fact that it's set in space in the distant future and will involve travel between different planets. The game had been in the planning stages for around a decade before development began in earnest after the release of Fallout 4's last DLC in 2016 (multiplayer game Fallout 76, released in 2018, was largely developed by a different team).
Given Bethesda's preference for confirming the release date for their games just 3-4 months before that date, some fans were holding out hope for a surprise announcement followed by a late 2020 release, but that's now comfortably out of the question.
Various rumours have been voiced about Starfield, including that it will abandon the protagonist voice acting of Fallout 4, is set in the distant future of the Fallout universe (after humanity has recovered from the nuclear war) and it will use new technology to provide a seamless experience with no need for separate indoor/outdoor loading areas, but these all remain unconfirmed. It is known that after Starfield, Bethesda will switch to full production on The Elder Scrolls VI, which is believed to have the (at least working) subtitle Redfall.
Gamers will have plenty to tide them over in the meantime, including CD Projekt Red's massive SF roleplaying game Cyberpunk 2077, which is due for release on 19 November this year.