Zcash NU7 Upgrade Goes Live, Locks $15M in Sprout Funds

Zcash’s NU7 network upgrade activated Friday, making about $15 millionin ZEC held in the network’s legacy Sprout shielded pool unspendable.

The upgrade took effect at block 3,543,405 at 02:34 UTC, according to blockchain tracker ZecStats, which lists the Sprout pool balance at about 12,224 ZEC.

The upgrade cuts Zcash’s target time between blocks from 75 seconds to 25, although actual block intervals will adjust toward the new target as mining difficulty changes. 

Under Zcash Improvement Proposal (ZIP) 2003, NU7 rejects version 4 transactions, the only format that supports spending Sprout funds. The remaining coins cannot be transferred under the new rules, but have not been burned. 

The specification leaves open the possibility that a future network upgrade could restore access, either by re-enabling version 4 transactions or introducing another mechanism to retrieve the funds. However, it warns that “the ability to spend Sprout funds may never be re-enabled.”

NU7 also introduces a Network Sustainability Mechanism that removes 60% of transaction fees from circulation for eventual reissuance through future mining rewards, starting around February 2031.

The upgrade preserves Zcash’s 21 million ZEC supply cap and halving schedule, while introducing limits on shielded activity designed to reduce wallet synchronization demands.