Ford states its 2014 Fiesta with a 120 horsepower EcoBoost 1 liter engine is rated at 45 mpg highway by the EPA
Ford CEO Alan Mulally with the 1.0-liter EcoBoost engine
Turbocharging gas mileage

It's been nearly a year, November 19th of 2012 to be precise, since Ford first announced its decision to bring over the diminutive 1.0-liter EcoBoost engine stateside.

I emphasize "stateside" because across the pond where it's available on no less than five nameplates, the company's smallest turbo has accounted for a compelling 32 percent of Focus sales and 26 percent of Fiesta sales so far this year. This demand even spurred Ford to double production capacity at the plant in Cologne, Germany where it's produced to more than 1,000 engines per day.
2014 Ford Fiesta SE with the 1.0-liter EcoBoost package
EPA numbers

Besides its SAE-certified 123 horsepower and 125 lb.-ft. of torque, a 1.0-liter EcoBoost-equipped Fiesta will now be the most fuel-efficient non-hybrid gasoline-powered car available in the U.S. That would be an EPA certified 45 mpg highway rating for a manually-equipped model in SE trim – eclipsing both the current Honda Fit (by 12 mpg) as well as the Toyota Yaris (by 8 mpg).

Other EPA figures for the same 6-speed manual SE come in at 32 mpg city and 37 mpg combined.

The Dearborn-based manufacturer also noted that an overboost function allows the force-fed engine to generate more than 145 lb.-ft. of torque for up to 15 seconds.

"With the new Fiesta 1.0-liter EcoBoost we're pushing into fuel economy numbers only seen on hybrids and diesels," said Joe Hinrichs, executive vice president and president of the Americas for Ford. "Coupled with the new Fiesta ST, Fiesta covers the performance-efficiency continuum in the subcompact segment better than any other nameplate in the market."
1.0-liter EcoBoost engine in the 2013 European Ford Focus
Achieving those numbers

Helping achieve those numbers, all Fiesta SEs equipped with the Manual EcoBoost Package will be the recipients of a plethora of aerodynamic aids including a rear spoiler, side air deflectors, underbody shields, lower grille blockers and low-rolling-resistance tires.
Ford 1.0-liter EcoBoost
Availability

According to Ford, the 2014 EcoBoost Fiesta will be arriving at dealers "later this year" and we're assuming that since nothing has been mentioned so far, pricing will become available closer to its release date.