Zcash is approaching a network upgrade that will make approximately 12,226 ZEC remaining in its original Sprout shielded pool unspendable under current consensus rules. According to the official NU7 deployment specification, Network Upgrade 7 activates at block 3,543,405 and will reject version-4 transactions, the only transaction format capable of spending Sprout funds. At recent ZEC prices near $1,300, the remaining balance is worth roughly $16 million.
The deadline is determined by block height rather than a fixed clock time. Estimates place activation during the evening of November 5 in the United States, although the exact moment will move with block production. Any ZEC still inside Sprout when block 3,543,405 arrives will remain part of Zcash’s issued supply but will no longer have a supported transaction format through which it can be spent.
Sprout Holders Lose Their Current Spending Path
Sprout was Zcash’s original shielded protocol when the network launched in 2016 and was later superseded by Sapling, Orchard and newer privacy infrastructure. Under ZIP 2003, NU7 changes Zcash consensus so that only version-5 and version-6 transactions remain valid. Because Sprout transfers can only be represented through version 4, disabling the format effectively freezes the entire remaining Sprout value pool.
The change affects more than Sprout transactions. Any preconstructed version-4 transaction, including transparent-only or Sapling transactions using that format, becomes invalid after activation and must be recreated using a supported transaction version where possible. Sprout is different because no equivalent v5 or v6 spending mechanism exists. A valid Sprout private key will therefore no longer be sufficient to move those funds once NU7 activates.
Holders have moved substantial value ahead of the cutoff. The Sprout balance declined from approximately 22,263 ZEC a week earlier to around 12,226 ZEC, including an exit of roughly 9,094 ZEC on November 1. The public pool balance reveals how much ZEC remains but cannot identify its owners or distinguish active holders from coins whose private keys may already be lost.
The freeze is not formally irreversible. ZIP 2003 explicitly declines to burn or unissue the remaining ZEC and leaves open a future consensus mechanism capable of retrieving it. There is nevertheless no approved recovery upgrade, and the specification warns that Sprout spending may never be restored. That makes the post-NU7 balance inaccessible indefinitely unless the network later adopts another mechanism.
NU7 Removes Legacy Code and Speeds Up Blocks
Retiring Sprout reduces a legacy verification burden that developers say remains inside critical transaction-processing paths despite minimal usage. The old JoinSplit circuit, nullifier handling and note commitments still add code and potential attack surface that node implementations must maintain. NU7 trades backward compatibility with a largely dormant privacy pool for a simpler consensus environment.
That security calculus has become particularly relevant after Zcash spent 2026 addressing weaknesses in newer privacy infrastructure. An Orchard soundness vulnerability forced an emergency soft fork followed by the NU6.2 upgrade, while subsequent analysis examined why the possibility of historical counterfeit ZEC could not be conclusively disproven. Those incidents involved Orchard rather than Sprout, but they illustrate the maintenance and verification costs created by multiple generations of shielded protocols.
NU7 also makes broader changes to network operation. Target block spacing falls from 75 seconds to 25 seconds, while the per-block subsidy drops proportionally so ZEC issuance per unit of time and the 21 million supply cap remain unchanged. The upgrade additionally introduces shielded-action limits and the Network Sustainability Mechanism. Faster blocks are intended to shorten confirmation latency, not triple Zcash’s monetary issuance.
The upgrade has been approaching through a defined rollout that was already visible when Zcash set its NU7 testnet and November mainnet milestones. The immediate consequence is now concentrated on a relatively small legacy pool: once block 3,543,405 is accepted, whatever ZEC remains in Sprout becomes stranded under the active consensus rules, while Sapling and newer supported pools continue operating.