Key Notes
- Sprout funds left at NU7 activation will become unspendable even with valid private keys.
- The upgrade targets 25-second blocks while preserving the daily issuance schedule.
- Sixty percent of transaction fees will enter the NSM for future mining rewards.
Zcash’s NU7 upgrade is set to make funds in its original Sprout privacy pool unspendable, leaving roughly 12,200 ZEC, valued at about $16 million, at risk of being stranded unless holders move them before activation.
The change takes effect at block 3,543,405, according to the deployment specification. The deadline follows the blockchain’s progress, rather than a fixed clock time. An early Thursday estimate placed activation around 02:30 UTC on November 6, or Thursday evening in the United States.
CoinDesk reported that about 12,226 ZEC remained in Sprout on Thursday morning, using ZecStats records. Its roughly $16 million valuation assumed a ZEC price near $1,300. Further withdrawals and price changes can alter that total before the cutoff.
Why Sprout Funds Will Become Unspendable
Sprout is the oldest generation of Zcash’s shielded payment system. NU7 will reject version 4 transactions, the only format capable of spending Sprout balances. Holding the correct private keys will therefore be insufficient to move coins left in that pool after activation.
The Sprout specification leaves those balances within issued supply. It allows for a future consensus change that could restore access, but explicitly warns that spending may never be re-enabled. Holders cannot rely on a later recovery mechanism.
Retiring Sprout removes legacy transaction-processing code and reduces the software’s complexity and attack surface. There is also a practical difficulty for remaining holders: the retirement of zcashd removed the only maintained software with Sprout wallet functionality, according to the specification.
Faster Blocks and More Shielded Capacity
NU7 reduces the target interval between blocks from 75 seconds to 25 seconds. That shortens the expected wait for a confirmation, although actual mining times vary and exchanges decide how many confirmations to require.
The scaling specification estimates Orchard-protocol capacity will rise from about 2.9 to 6.6 transactions per second under its transaction assumptions. These are capacity estimates, rather than a measurement of current demand or a promise that every payment will settle in 25 seconds.
New limits on shielded activity also constrain spam. The specification estimates they reduce the worst-case daily synchronization bandwidth imposed on light wallets by about 37%, despite the increased number of blocks.
Fees Build a Reserve for Future Mining Rewards
Under new fee rules, 60% of each block’s transaction fees will leave circulation through the Network Sustainability Mechanism, or NSM. Miners retain the other 40%. The withheld fees are intended for later algorithmic reissuance through block rewards.
The Zcash Foundation says reserve reissuance begins at block 8,939,664. Per-block subsidies fall to one-third of their previous level to offset faster blocks, preserving the daily issuance schedule, four-year halving cycle and 21 million ZEC ceiling.
This fee change is separate from the withdrawn grants plan that proposed redirecting existing and future Zcash Community Grants funding into the NSM.
Operators Must Upgrade Before Activation
The Foundation instructs mainnet node operators to install NU7-compatible software before block 3,543,405. Unsupported nodes can follow a different chain after activation. Wallets and transaction services must also stop constructing version 4 transactions, a restriction that covers more than Sprout transfers alone.
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