The Barron's 400 ETF (ticker: $BFOR) has experienced a significant inflow of $600 million, dramatically increasing its total assets from $200 million to $800 million. This surge comes after 13 years of relative obscurity for the fund. The ETF has been outperforming the market year-to-date, which may have attracted new investment models. Despite the substantial increase in size, the fund's percentage premium remained stable, highlighting the potential for rapid growth in ETF assets without affecting pricing.