The U.S. SEC has acknowledged Grayscale Investments' filing for a Cardano (ADA) exchange-traded fund (ETF).The SEC will assess whether the ETF meets federal securities law requirements during the 180-day review period.If approved, it would be the first-ever spot ADA ETF in the United States.Grayscale's push for a Cardano ETF reflects growing institutional interest in altcoin investment products.