Bitcoin miners are making hay while the sun shines. The next halving is expected in April 2024, a process designed to slow the release of bitcoin, whose supply is capped at 21 million - of which 19 million have already been mined. "You're seeing a lot of urgency to plug rigs in ahead of the halving," said Gregory Lewis, analyst at brokerage BTIG that covers the 13 biggest U.S.-listed bitcoin miners.