Zynga’s stock price rose as high as 15 percent in early trading on Nasdaq as the company went public at $10 a share.

[Update: at 12:10 pm Eastern time, Zynga’s stock has fallen to $9.88 a share]

Raising at least $1 billion, Zynga’s debut on the stock market is the biggest tech IPO in the U.S. since Google went public in 2004 and the biggest IPO in the history of the game industry. Trading under the symbol ZNGA, the stock rose to $11.22 a share at 11:49 am and has risen as high as $11.50 so far today.

Zynga had estimated its price would be about $8.50 to $10 a share in its pre-IPO roadshow, but it priced the stock at the high end of that range, valuing the company, including options, at $8.9 billion. Online game company Nexon, by contrast, which IPO’d two days ago, raised $1.2 billion on the Tokyo Stock Exchange and saw its stock fall in the first couple of days of trading.

Zynga is offering around 14 percent of its common stock, or about 100 million shares. Underwriters have the option to buy 15 million more shares to cover over-allotments, which means Zynga could raise as much as $1.15 billion. Back in July, when Zynga filed, rumors were that Zynga’s value would be $15 billion to $20 billion, and in August, a third-party estimate put Zynga’s value at $14.1 billion. But now the public market is the ultimate test for Zynga and its vision to make everybody into a social gamer, as chronicled in our extensive story on the history of Zynga.