Zcash NU7 Upgrade Goes Live, Rendering $15 Million in Sprout Funds Unspendable
Key Takeaways
- •Zcash's NU7 upgrade activated Friday at block 3,543,405, making about $15 million worth of ZEC in the legacy Sprout shielded pool unspendable.
- •ZIP 2003 prohibits version 4 transactions, the sole format able to spend Sprout funds, so roughly 12,224 ZEC remain on-chain but cannot be transferred.
- •A future network upgrade could restore access to the Sprout pool, though the specification warns that spending may never be re-enabled.
- •NU7 reduces Zcash's target block time from 75 seconds to 25 seconds and imposes limits on shielded activity to ease wallet synchronization.
- •The new Network Sustainability Mechanism removes 60% of transaction fees from circulation for reissuance through mining rewards starting around February 2031, while the 21 million ZEC supply cap and halving schedule stay intact.
Zcash, the privacy-focused cryptocurrency, activated its NU7 network upgrade on Friday, rendering approximately $15 million in 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. Sprout, the oldest of Zcash's shielded pools, dates back to the protocol's 2016 launch and has since been superseded by newer shielded pools introduced in later upgrades.
The stranded funds are the result of NU7's revised transaction rules. Under Zcash Improvement Proposal (ZIP) 2003, the upgrade rejects version 4 transactions — the only format that supports spending funds from the Sprout pool. The coins therefore cannot be transferred under the new consensus rules, although they have not been burned. The outcome underscores a practical reality of consensus changes: holdings tied to legacy formats can become unspendable even while they remain recorded on the chain.
The specification leaves open the possibility that a future network upgrade could restore access, either by re-enabling version 4 transactions or by introducing another mechanism to retrieve the funds. However, the document also warns that "the ability to spend Sprout funds may never be re-enabled." Any decision on the pool's fate would therefore surface through Zcash's future network upgrade process.
NU7 also brings broader performance and monetary changes. It cuts Zcash's target time between blocks from 75 seconds to 25 seconds, although actual block intervals will adjust toward the new target as mining difficulty changes.
The upgrade additionally introduces a Network Sustainability Mechanism, which removes 60% of transaction fees from circulation for eventual reissuance through future mining rewards, beginning around February 2031.
Despite these changes, NU7 preserves Zcash's 21 million ZEC supply cap and its existing halving schedule. It also introduces limits on shielded activity designed to reduce wallet synchronization demands for users.
