There is a theoretical upper bound on the number of UTXOs that can exist, but it comes from a consensus serialization limit, not from an explicit “UTXO cap” rule. The UTXO set is stored as a map keyed by outpoints: (outpoint) = (txid + vout) vout is serialized as a 32-bit unsigned integer (uint32) So the theoretical maximum outputs per transaction is: 4,294,967,296 outputs With a 4 MB weight block, the practical maximum outputs in a block is roughly 90k–120k outputs. So the real constraint is block weight, not the 32-bit index. So if EVERYONE wanted to move their coins to self-custody over the next week, it's literally impossible. The chain could only process 4–6% of such demand in a week.