In v4, most of the operators filter BGP updates for prefixes longer than a /24, to preserve the size of the full view.
What about IPv6 ? Is there such "convention" that stands out ?
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These days it's usually at /48, and it's very unlikely to ever be longer.
There are still AS' filtering longer than /32 though, but they should all have a default at this point (Verizon were a hold-out, but I believe they've given up).
There are also AS' filtering on allocation lengths, so if you got a /32 they might require you advertise it as such (based on the various RIR's documented allocation policies).