Tether, the most popular stablecoin in the world, has invested $50 million in sleep tech startup Eight Sleep at a $1.5 billion valuation. The investment is part of Tether's strategy to develop new AI health features using its QVAC architecture, which processes data at the device level rather than relying on cloud systems. This investment is the latest in a trend that Tether is expanding beyond stablecoins and other forms of innovation.