It's not that S6 mules haven't been seen before. They have. Still, one spotted on US soil in US trim is another matter entirely. Looking much like an A6 S-line save for the quad tailpipes, we're guessing this navy blue mule didn't even stick out much in traffic. After all, dealers are receiving their demo A6s already. Fortunatley, photographer Jeremy Kupfer was eagle eyed and noticed the two extra pipes.
So what do we know about the S6? Expect it to be powered by Audi's new 4.0T tuned to 408 hp as per this uncovered Russian Audi ETKA scan that reveals details about the car. That scan also suggests the S6 will be on the market by November of this year, so we expect to see the S6 live and in the alloy no later than the Frankfurt IAA in September.
Read more about this US-spec S6 tester and see several more photos at Car & Driver after the jump.