That's right!, Kanye rented out AT&T park for Kim's birthday and had a 50-piece Orchestra band playing "Young and Beautiful," Keri Hilson, Ne-Yo and Yeezy's, "Knock You Down," while he got down on one knee with a 15-carat diamond ring. The huge stadium is also home to the San Francisco Giants.
Via E!:

The E! star is engaged to longtime love Kanye West, the rapper popping the question in front of their friends and family at AT&T Park in San Francisco.  

Kanye, whose Yeezus Tour touches down in nearby San Jose tomorrow night, rented out the stadium for the occasion.

It has been rumored for a while now that the two were talking about marriage. They already have a house and lets not forget about their first child, North West. Lets just hope the couple doesn't make a huge reality TV special out of it.