TL;DR
The undersea home is back. For decades the idea of people living on the ocean floor belonged to science fiction and a few research stations. Now a company called DEEP has set down the first new subsea habitat in decades, a living space for up to four people, on the seabed 56 feet below the Florida Keys. It is shallow, tethered to a buoy at the surface, and still in testing, and nobody can say for certain whether anyone has slept there yet. But if it clears its last checks, living under the sea for days at a time could become something more people than professional divers get to do. The floating cities that were promised alongside it are a different story: the flagship project has missed every date it set.
Below the line, for paid subscribers: The full story: where it stands, how we got here and what's dated next; our Odds board on 5 milestones, starting with "A crewed mission aboard Vanguard is publicly confirmed by 2027"; and every source.