CEO Sundar Pichai defended the dramatic increase on a conference call with analysts, who are raising new questions about capital spending.

Alphabet said on Tuesday it will spend $75 billion on its AI buildout this year, 29% more than Wall Street expected, while posting cloud revenue that missed analysts' target.The tech giant's shares were down 9% in extended trading.

The search giant said it will spend a staggering $75 billion this year as the AI arms race heats up. Investors may have concerns about whether it will pay off. Shares in Google’s parent company, Alphabet (Nasdaq: GOOG),