Zcash’s NU7 network upgrade activated on Friday at block 3,543,405, effectively locking funds held in the protocol’s legacy Sprout shielded pool. The activation occurred at 02:34 UTC, according to data from ZecStats.
The upgrade renders the remaining 12,224 ZEC in the Sprout pool unspendable under the new consensus rules. While the funds have not been burned, they cannot be transferred because NU7 rejects version 4 transactions, which are the only format that supports spending Sprout funds under Zcash Improvement Proposal (ZIP) 2003.
Protocol specifications warn that the ability to spend these stranded Sprout funds may never be re-enabled.
Block time reduction and sustainability mechanism
Beyond addressing legacy privacy pools, NU7 introduces significant changes to Zcash’s emission and transaction processing parameters. The upgrade reduces the target time between blocks from 75 seconds to 25 seconds.
The update also implements a Network Sustainability Mechanism. This feature removes 60% of transaction fees from circulation rather than distributing them entirely to miners. These withheld fees are designated for eventual reissuance through future mining rewards, scheduled to begin around February 2031.
Despite these structural adjustments, NU7 preserves Zcash’s hard cap of 21 million ZEC and maintains the existing halving schedule.
