December 2022. I'll certainly announce it on my twitter, if you need a place to get a reminder (@droqen)
edit : accidentally wrote 2023 for some reason! it's 2022
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The jam with the longest upcoming time is actually at the end of human civilization, the last jam, after which all jammers will finally die out or be too resigned to have another one. They might not know it's the last jam when they're having it.
Anyway, that one is probably at least a few decades out but probably a lot longer! But it hasn't been preannounced on itch.io yet, similarly to VMJ 2023. Go join some other, sooner jams, in the meantime!