This U.S. expansion may be moving like a tortoise, but it's on its way to win the race.

Widely disdained for its relatively weak growth and pay gains, the expansion is about to complete its eighth year, and it's headed to become the longest on record, according to a Bloomberg survey of economists. Respondents put a 60 percent probability, based on the median estimate, on the growth streak running through at least July 2019 and thereby reaching 121 months, topping the 10 years of gains during the 1990s.

They're betting on it even as the Federal Reserve raises interest rates and President Donald Trump's fiscal policy-induced bump increasingly seems more hope than reality. As the economy made up lost ground after the financial crisis, the lack of big spurts or excesses resulted in an expansion that's more slow and steady, which makes it well-placed to be extended.