Zcash NU7 Upgrade Sparks Controversy: What Happened to 12,224 ZEC Locked in Sprout Pool?

Ever wondered what happens when $15 million worth of Zcash suddenly becomes untouchable overnight? Well, Zcash’s NU7 network upgrade flipped that script this Friday, freezing about 12,224 ZEC in the legacy Sprout shielded pool—making those coins unspendable under the new rules. This upgrade, which kicked in at block 3,543,405, doesn’t just tweak the blockchain’s inner workings by slashing the target block time from 75 to 25 seconds—it throws a curveball at old Sprout funds by ditching version 4 transactions, the only way to spend them. It’s like locking a treasure chest and tossing away the key… or at least, for now. The upgrade also unleashes a Network Sustainability Mechanism, siphoning 60% of transaction fees out of circulation for future miners’ rewards, set to roll out in 2031. All while keeping Zcash’s supply cap and halving schedule intact, plus adding limits to shielded activity to ease wallet syncing woes. The million-dollar question? Will those frozen Sprout funds ever thaw, or are they destined to be digital ghosts haunting the blockchain? Intrigued yet? LEARN MORE.

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.