The U.S. GENIUS Act officially took effect on April 1, 2026, marking a significant regulatory milestone for stablecoins. The U.S. Department of the Treasury and the Office of the Comptroller of the Currency (OCC) have opened a 30-day registration window for "Permitted Payment Stablecoin Issuers" (PPSI), requiring major issuers like Circle and Paxos to apply for compliance. This move aims to bring stablecoins under federal regulation, mandating that they be backed 1:1 by cash or short-term U.S. Treasuries. The GENIUS Act's implementation introduces a dual federal and state regulatory framework, allowing stablecoins with issuance volumes under $10 billion to operate under state-level regulations deemed "substantially equivalent." This framework could lead to regulatory arbitrage, as noted by institutions like CSIS and the Brookings Institution. The Act's reserve asset requirements are expected to impact the short-term Treasury market, potentially suppressing yields as compliant stablecoins increase their holdings. The GENIUS Act represents the first comprehensive federal legislation targeting payment stablecoins in the U.S., aiming to redefine "legal tender USD" and establish who is qualified to issue it. The Act's enforcement phase is seen as a critical juncture for the stablecoin market, with potential structural realignments expected over the next 90 days as issuers navigate the new regulatory landscape.