Zcash's proposed NU7 upgrade would close spending from Sprout, the oldest privacy pool, which held about 22,309 ZEC on Oct. 17. Holders could retain private keys but lose the ability to move those funds on the upgraded network. The NU7 deployment specification leaves the mainnet activation height unassigned, with a final decision planned for Oct. 20 after testnet experience. Nov. 5 remains the target, conditional on that decision. The zkp.baby dashboard recorded 22,309.44195128 ZEC in Sprout at block 3,521,260, updated at 19:10:09 UTC on Oct. 17.
ZIP 2003, whose listed owner is Daira-Emma Hopwood, proposes rejecting version 4 transactions from NU7 onward. Sprout transfers require version 4 because neither version 5 nor version 6 supports Sprout transfers. The restriction would cover every version 4 transaction, including transparent-only and Sapling transactions. Users can recreate non-Sprout transactions in a supported format where possible. However, Sprout has no equivalent replacement. Merely re-signing a version 4 transaction cannot fix the invalid format. Newer transaction formats also need signatures appropriate to the consensus branch.
ZIP 2003 explicitly leaves Sprout's remaining balance in issued supply. ZIP 2003 allows the theoretical possibility of re-enabling version 4 transactions or creating another retrieval facility, while warning that spending may never be restored. Zallet's migration documentation excludes Sprout spending keys and funds from the import process and tells users to preserve the original wallet.dat.
The Argos recovery tool documents a recovery route for holders with a legacy wallet file or standalone Sprout spending keys. A wallet containing usable note data and a cached witness can avoid a historical scan. Recovery with a key alone may require reconstructing additional data needed to build a valid spend. Argos estimates roughly 280 GB of transfer and potentially days of processing for a full-block scan, while retaining less than 500 MB on disk. Argos documents that Sprout sweeps send funds to Sapling, a newer shielded pool, even when a Unified Address is supplied. Moving recovered funds onward is a separate operation.
Exiting involves fees and recovery work as well as a privacy trade-off. ZIP 308's migration design explains that Sprout-to-Sapling value passes through public pool accounting, exposing the amount without requiring a transparent address. ZIP 308 specifies coordinated transaction timing and randomized amounts to reduce the chance of linking individual transactions. ZIP 2003 warns that a short or poorly coordinated exit period can make distinctive amounts and timing easier to associate with holders.
Hopwood's proposal says Sprout's specialized verification and handling of private notes and spent-note identifiers still add work to live transaction acceptance despite little use. Verification costs also affect denial-of-service exposure in pending-transaction and block processing. Sprout shares cryptographic components with Sapling, and pool accounting checks limit potential balance violations. The proposal argues that these safeguards leave Sprout-specific complexity to maintain and that retirement would reduce the burden for implementations validating the network. ZIP 211 stopped new value entering Sprout while preserving withdrawals of existing funds. ZIP 2003, created on Oct. 31, 2024, would close spending under NU7.
The Zcash Foundation announced Zebra 7.0.0-rc.0 on Oct. 2, scheduling NU7 at testnet height 4,465,026 around Oct. 6. An Oct. 10 engineering reply confirmed that testnet had passed activation. A September coordination announcement posted by the forum account ebfull reported agreement among ecosystem organizations and engineering teams after polling and discussions. Earlier coverage described the coinholder poll result as advisory.
Zcash upgrades activate at a specified block height. ZIP 259 waives NU7's usual recommendation of roughly three months after the first supporting release and the requirement tied to deprecation of unsupported software. ZIP 259 warns that unsupported software may remain online and follow pre-NU7 rules, so operators need compatible software to validate the upgraded network. A community recovery thread published Sept. 20 adds to the public notice history. Approval and an assigned mainnet height would establish an operational cutoff before which Sprout holders would need to confirm a valid migration.
Zcash's NU7 Upgrade to Freeze Sprout Pool, Rendering Funds Unspendable
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Summary
Zcash's upcoming network upgrade, NU7, will freeze the Sprout privacy pool, locking around 22,309 ZEC as of October 17. Users will keep private keys but can't spend the funds post-upgrade. ZIP 2003, by Daira-Emma Hopwood, blocks version 4 transactions, including Sprout transfers, from NU7 onward. The blockchain upgrade's activation height is pending, with a final decision due October 20. Zebra 7.0.0-rc.0 was released October 2, with testnet activation around October 6.
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