apxUSD is a synthetic U.S. dollar token backed by an overcollateralized basket of low-volatility, variable-rate preferred shares issued by Digital Asset Treasuries. The collateral basket is dynamically allocated and rebalanced subject to concentration, liquidity, and coverage constraints. Peg support uses (i) preferred-share price dynamics near par, (ii) overcollateralization, (iii) arbitrage via whitelisted mint/redemption pathways, and (iv) tail-hedging tools. General users obtain apxUSD through external liquidity pools and swaps.