As of right now:
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kbin.social has 36,508 total users: https://fedidb.org/network/instance/kbin.social
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lemmy.ml has 36,185: https://fedidb.org/network/instance/lemmy.ml
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lemmy.world has 33,945: https://fedidb.org/network/instance/lemmy.world
Well done, kbinauts!
(For completeness: Lemmy as a whole is still much larger than kbin by 330,192 users to 41,477.)
Pixelfed is the instagram one.