Final answer:
The US Open Championships were initially played on grass courts, but the surface has changed to hard courts today.
Step-by-step explanation:
The US Open Championships were initially played on grass courts. However, the surface has changed over time, and today the tournament is played on hard courts. The US Open Championships, one of the four Grand Slam tournaments in tennis, were initially played on grass. Specifically, from the tournament's inception in 1881 until 1974, the surface was grass. However, there have been changes to the surface over the years. From 1975 to 1977, the Championships were played on clay. Since 1978, the US Open has been played on a hardcourt surface, known as DecoTurf. This surface continues to be used today. Hardcourts generally provide a consistent bounce of the ball and are considered a neutral ground for various playing styles, balancing the advantages between players who prefer different types of surfaces.