The Prius c is a concept in name only, because this smaller and even more fuel-efficient variant is going into production.

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We had a less expensive version of the Prius -- the Prius C as it's marketed in the U.S. We've had new Lexus launches, relaunches of the Avalon and RAV 4.

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At the same time, as Automotive News noted, before this report, the largest mileage discrepancies found by Consumer Reports were 7 and 6 mpg for the Prius c and regular Prius.

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