The oldest exchange-traded fund listed in the U.S. has just been surpassed in assets under management by a Vanguard ETF that more cheaply tracks the S&P 500 index.

Vanguard Group's Standard & Poor's 500 ETF overtook rival State Street Global Advisors' SPDR S&P 500 Trust, on Tuesday to become the world's largest exchange-traded fund, according to data from FactSet.

Vanguard's S&P 500 exchange-traded fund is now the largest in the world by assets, grabbing a title that State Street's SPDR S&P 500 ETF Trust—better known by its ticker SPY—held for most of the last 30 years.