When released in the fourth quarter of this year, Hyundai anticipates its most-efficient version of the Ioniq Hybrid will net as much as 57 or 58 mpg combined on the U.S. EPA cycle.

Assuming federal certification bears out Hyundai’s internal testing, its purported “Prius fighter” – as media have portrayed it – will be aptly described because the most-efficient 2016 Toyota Prius Eco is rated 56 mpg combined, while five other trims yield 52 mpg.

The Ioniq has launched in Korea already, and for the U.S., a version with 15-inch wheels will be the most fuel efficient, said John Shon, manager of product planning today in New York.

Models equipped with larger and wider 16- and 17-inch wheels (pictured) are expected to be EPA rated incrementally lower, but Shon did not venture a guess.

Hyundai’s hybrid utilizes a 1.6-liter Atkinson cycle direct injected engine with Prius-equaling 40-percent thermal efficiency. Its single motor hybrid system delivers power through a six-speed dual-clutch automatic transmission touted as relatively better on the highway than a continuously variable unit in a Prius.

SEE ALSO: Who Else Besides Toyota Will The Hyundai Ioniq Threaten?

Its coefficient of drag is also a Prius-equaling 0.24.

Hyundai's estimates are according to its internal testing which are projected to be verified by the EPA.

Hyundai’s estimates are according to its internal testing which are projected to be verified by the EPA.

The Korean version was already recalled for a software update after press there discovered an issue where it might lose power and roll backward down hill after a stop in EV mode.

The update was made, models now being produced in Korea are no longer affected, and U.S. models will likewise be free of the concern, said Derek Joyce, manager, Product Public Relations.

When the Ioniq Hybrid is launched in the U.S. it will soon be followed by a battery electric Ioniq version with 110 miles or so range – also subject to EPA certification.

A few months after, early next year, a plug-in hybrid Ioniq version will also be released. This too will beat a Prius – the plug-in hybrid “Prius Prime” introduced today and rated 22 miles from its 8.8-kwh li-ion battery.

Shon says the 8.9-kwh lithium-polymer battery in the Ioniq will be good for more than 25 miles but and less than 30 miles range before resorting to high-efficiency hybrid mode operation.