Alphabet became the world’s largest company by market capitalization after its 2015 restructuring.
Google created Alphabet as a new holding company in 2015, with the restructuring taking effect in October of that year. Google became Alphabet’s largest subsidiary, while other businesses and long-term projects were grouped under the wider corporate structure.
Alphabet briefly surpassed Apple in market capitalization in February 2016 after reporting strong quarterly results. The change highlighted the importance of Google’s advertising business, especially search advertising, alongside growth in YouTube and the cloud division.
The answer is Alphabet rather than Google because Alphabet became the publicly traded parent company. Google remained the best-known operating subsidiary, which is why headlines and casual references sometimes use the two names interchangeably.