CryptoSlate
Zcash's proposed NU7 upgrade would reject version 4 transactions, the format required to spend funds from the legacy Sprout pool. About 22,309.44195128 ZEC remained in Sprout at block 3,521,260 on Oct. 17, leaving holders dependent on migration before any mainnet cutoff.
Mainnet activation remains undecided. A decision is planned for Oct. 20 after testnet experience, while Nov. 5 remains a conditional target. The NU7 deployment specification has not assigned an activation height.
Why it matters
A private key alone would not preserve access if the network rejects the transaction format needed to use it. ZIP 2003 proposes closing the spending route for every version 4 transaction from NU7 onward. Newer version 5 and version 6 formats do not support Sprout transfers, leaving the pool without a direct replacement.
Migration also carries operational and privacy costs. Zallet's migration process excludes Sprout spending keys and funds, while the Argos recovery tool may require a legacy wallet file, standalone keys and a full historical scan. Argos estimates roughly 280 GB of data transfer and potentially days of processing when the required wallet data is unavailable.
Market impact
Sprout exits move funds into Sapling through public pool accounting, exposing the amount even when users do not use a transparent address. ZIP 308 describes coordinated timing and randomized amounts to reduce linkability, but ZIP 2003 warns that a short or poorly coordinated exit period could make amounts and timing easier to associate with holders.
The upgrade would reduce the validation burden created by Sprout-specific verification and spent-note handling, but shifts the migration burden to users. ZIP 2003 leaves open the theoretical possibility of restoring version 4 spending or creating another retrieval facility, while warning that spending may never return. Approval and a mainnet height on Oct. 20 are the next key signals for Sprout holders.
Frequently asked questions
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How much ZEC remained in the Sprout pool?
The Sprout pool held about 22,309.44195128 ZEC at block 3,521,260, according to the dashboard data cited in the report.
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Why would private keys not be enough after NU7?
A private key authorizes a spend, but the network must also accept the transaction format carrying it. NU7 would reject version 4 transactions, which Sprout transfers require.
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When will Zcash decide whether to activate NU7?
A mainnet decision is planned for Oct. 20 after testnet experience. Nov. 5 remains a conditional activation target, and the final activation height has not been assigned.
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What does Sprout recovery require if wallet data is missing?
Argos may require a legacy wallet file or standalone Sprout spending keys. A full historical scan can involve roughly 280 GB of data transfer and potentially days of processing.
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What privacy cost comes with moving Sprout funds?
Sprout-to-Sapling migration uses public pool accounting, which exposes the transfer amount even without a transparent address. Coordinated timing and randomized amounts are designed to reduce linkability.
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