As previously stated, there's no official style guideline for it.
Being a west-coaster, I tend to think of EPA being what's described by local HB club Maltose Falcon's style guidelines:
See Category 10.
However from their commercial examples, the Summit EPA is conspicuously absent: Commercial Examples: Alesmith X, Mad River Steelhead Xtra Pale Ale, BJ’s West Coast Xtra Pale, Green Flash Extra Pale Ale, SLO Brewing Extra Pale Ale, Three Floyds Extra Pale Ale
Essentially you're looking at lighter in color than APA category, lower ABV than IPA, but more aggressively hopped than APA.
But again, this "style" is not an exhaustive list. Different breweries can do a lot of different things and call them EPA.