Zcash’s NU7 upgrade could turn $16 million into very expensive legacy software 🧊

Zcash’s NU7 upgrade is scheduled for block 3,543,405, expected Thursday evening in the United States, and will render roughly 12,224 ZEC in the network’s original Sprout privacy pool unspendable. At recent market prices, those coins represent approximately $15 million to $16 million that could remain inaccessible even to holders with the required passwords and private keys. The activation time depends on the blockchain’s pace in processing new blocks rather than a predetermined clock time.

“NU7 (block 3,543,405) makes v4 transactions invalid, so what remains in Sprout is unspendable: frozen, not burned,” Zecstats says in its information card for Sprout. The change eliminates the only transaction format capable of moving coins out of Sprout, although the pool has already been closed to new deposits for years. Legacy Sprout addresses begin with “zc,” which can help users identify affected wallet records.

The upgrade removes Sprout’s outdated privacy technology, which consumed substantial computing resources and created complexity and potential security risks. Zcash introduced Sprout when the network launched in 2016, later adding the improved Sapling, Orchard, and Ironwood privacy systems. Zcash uses zero-knowledge proofs to verify transactions without revealing transaction amounts or the addresses involved.

The affected ZEC will continue counting toward Zcash’s circulating issuance calculations. A future network upgrade could theoretically restore spending access, but the technical specification warns that it may never be re-enabled. Users whose ZEC remains in Sprout must use a compatible withdrawal mechanism before NU7 activates; regular holders using modern supported wallets do not need to migrate coins out of Sprout, though keeping wallet software updated remains important.