Looks like a Big Zac!
They crack like that (at least the ones I've grown) I'm up to F5 this year. Though no monsters, most are around 2 lbs...
I think sun has a lot to do with it as does uneven watering, had good luck last year wrapping white sheets around the tomato cage for added shade. It seemed to reduce the cracks on a couple varieties ( George Detsika's, Pineapple Pig, Goldman's )
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