The New England-style India pale ale, with its juicy hop flavors and hazy look, has become a phenomenon among craft beer fans. They camp out overnight to be among the first to buy rare releases, and flock to hazy-I.P.A. festivals in New York City, Buffalo, Toronto and Portland, Ore., to celebrate the new vanguard.

Now comes proof that the groundswell is more than just a passing tremor: Two of the country’s largest craft brewers are making their own versions of the style. In December, Sierra Nevada Brewing Co. introduced Hazy Little Thing I.P.A. in a few areas, and this month has released it nationwide. The Boston Beer Company, which makes Samuel Adams, has begun selling its New England I.P.A. in that region, and will go nationwide in February.

For these companies, the move is both a logical next step and a big risk. Much of the appeal of the hazy I.P.A.s stems from their origins as small-batch, indie brews that are sold at the source. And unlike any earlier styles, these beers require freshness in the extreme. After a few weeks, they literally fall apart — the haze disappears as their proteins fall out of suspension, destroying the hop flavors and, in most cases, rendering the beer fit for the drain.

“Hazy I.P.A.s are pretty tough to make if you’re hoping to distribute nationally,” said Bill Manley, who helped develop Sierra Nevada’s recipe for Hazy Little Thing before leaving the company in November. “The haze that’s in beer is, by and large, pretty darn unstable.”