Zcash’s NU7 Upgrade Puts $16M Sprout Balance at Risk
About 12,226 ZEC remained in Zcash’s Sprout pool before NU7, which will disable the only transaction format that can spend the coins left there.
About Crypto Newsroom2 min read
12,226 ZEC, worth about $16 million, remained in Zcash’s Sprout pool Thursday morning as the network approached an upgrade that will make those coins unspendable. CoinDesk reported that the estimate uses a price of roughly $1,300 per ZEC and that holders can still move funds before activation.
Sprout is Zcash’s oldest shielded pool, where transaction details can be hidden. It launched with the network in 2016. The remaining balance was down from about 22,263 ZEC a week earlier, with most of the decline occurring Sunday, according to CoinDesk’s account of ZecStats’ historical records.
How will NU7 stop Sprout spending?
NU7 will reject version-4 transactions, the only format that can spend Sprout funds. The upgrade is scheduled to activate at block 3,543,405.
Zcash’s ZIP 2003 specification sets out the change. It says version-5 and version-6 transactions do not support Sprout, so coins left in the pool cannot be spent under the new rules.
Why is Zcash removing the old transaction format?
The specification says retiring version 4 removes obsolete complexity from Zcash’s transaction checks. Sprout is now essentially unused, but its older code still adds work to the software that validates payments and can increase exposure to denial-of-service attacks.
NU7 also reduces the target time between blocks from 75 seconds to 25 seconds. That change is separate from Sprout’s retirement and applies across the network.
Are the remaining coins permanently lost?
They remain part of Zcash’s issued supply, according to ZIP 2003. The specification leaves open a future change that could restore a way to spend them, but says access may never be re-enabled.
The public pool balance does not show who owns the remaining coins or how much may be held in wallets with lost keys. For holders, the next number to watch is block 3,543,405, when NU7’s new transaction rules take effect.
Sources and documents
- CoinDesk reported — coindesk.com
- Zcash’s ZIP 2003 specification — zips.z.cash