Zcash’s NU7 Upgrade Locked $15M in Legacy Sprout Funds

Zcash’s NU7 network upgrade activated and rendered legacy Sprout funds unspendable under the new rules. The upgrade went live at block 3,543,405 at 02:34 UTC, according to blockchain tracker ZecStats, which also listed the Sprout pool balance at about 12,224 ZEC—roughly $15 million at recent prices.

Why Sprout funds can’t move

Under Zcash Improvement Proposal (ZIP) 2003, NU7 rejects version 4 transactions—the only format that supports spending Sprout funds. As a result, the remaining Sprout coins cannot be transferred. The specification notes the coins have not been burned and leaves open the possibility that a future network upgrade could restore access, either by re-enabling version 4 transactions or adding another retrieval mechanism. It also warns that “the ability to spend Sprout funds may never be re-enabled.”

Block timing and network changes

NU7 cuts Zcash’s target time between blocks from 75 seconds to 25 seconds. Actual block intervals will adjust toward the new target as mining difficulty changes.

Fees, supply, and shielded limits

The upgrade introduces a Network Sustainability Mechanism that removes 60% of transaction fees from circulation for eventual reissuance through future mining rewards, starting around February 2031, per the specification. NU7 preserves the 21 million ZEC supply cap and the halving schedule, and it adds limits on shielded activity intended to reduce wallet synchronization demands.