Boom XB-1, which is funded by YCombinator: https://boomsupersonic.com/xb-1 https://boomsupersonic.com/xb-1 Note that they're targeting a very different market

Boom XB-1, which is funded by YCombinator: https://boomsupersonic.com/xb-1 https://boomsupersonic.com/xb-1 Note that they're targeting a very different market segment from most commercial aviation - they're going for supersonic overseas business travel at a premium price point. Hence, relaxing some constraints. Even then it's taken 10 years to go from seed funding to first flight, and they're still far away from a commercial flight.