Here are 28 house seats. Which will have the closest result? Resolves when final results are tallied, and resolves to whichever group of four has the seat with the smallest margin. This market will close on election night, but will probably be resolved sometime around January 6th, possibly earlier if we're lucky.
All districts were listed as "Toss Up" by Cook Political Report as of 10/24, plus two additional seats (MI-10 (James) and PA-17 (Deluzio), which were categorized as "lean republican" and "lean democrat" seat, respectively). They've been bundled into random groups of 4 together because it feels so much easier betting on 7 seats than betting on 28 individual seats. This market resolves to whichever of these 7 options contains the closest race.
I'm calling it. CA-13, which was decided by a margin of 187 votes.