Zcash NU7 Upgrade Leaves 12,224 ZEC Unspendable

Zcash’s NU7 network upgrade took effect at block 3,543,405 at 02:34 UTC on Nov. 6. It left about 12,224 ZEC in the network’s legacy Sprout shielded pool unable to be transferred under the new rules. The coins remain on the blockchain and have not been destroyed.

Under Zcash Improvement Proposal 2003, NU7 rejects version 4 transactions. These were the only transactions that could spend funds held in the Sprout pool.

The upgrade cuts Zcash’s target time between blocks from 75 seconds to 25 seconds. Actual block intervals are expected to move toward the new target as mining difficulty adjusts.

The NU7 specification allows a future network upgrade to restore access to the funds by re-enabling version 4 transactions or adding another way to retrieve Sprout holdings. It also states that access to the funds may never be restored.

NU7 introduces a Network Sustainability Mechanism that removes 60% of transaction fees from circulation. The funds are scheduled for possible reissuance through future mining rewards beginning around February 2031.

The upgrade preserves Zcash’s 21 million ZEC supply cap and existing halving schedule. It also limits shielded activity to reduce the computing and storage requirements for wallets that synchronize with the network.

Reviewed and fact-checked by Alex Panasenko on November 6.