Zcash NU7 proposal would freeze about 22,309 ZEC in its legacy Sprout pool

What ZIP 2003 proposes

The change is laid out in ZIP 2003, a Zcash improvement proposal whose listed owner is Daira-Emma Hopwood. It proposes rejecting version 4 transactions from NU7 onward.

The restriction technically reaches every version 4 transaction, including transparent-only and Sapling ones. The consequences differ by pool, though. Transparent-only and Sapling transactions can be recreated in a supported format where possible, CryptoSlate noted. Sprout has no equivalent replacement (its transfers require version 4, and neither version 5 nor version 6 supports them).

The funds wouldn't disappear. ZIP 2003 keeps Sprout's remaining balance in issued supply and allows for the theoretical possibility of re-enabling version 4 transactions or building another retrieval facility. It also warns that spending may never be restored.

Hopwood's proposal argues that Sprout's specialized verification and its handling of private notes and spent-note identifiers add work to live transaction acceptance even though the pool sees little use. It also ties those costs to denial-of-service exposure in pending-transaction and block processing. (It notes that Sprout shares cryptographic components with Sapling, and that pool accounting checks limit potential balance violations.)

Timing is still open

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, CryptoSlate reported. The NU7 deployment specification leaves the activation height unassigned, with a final decision planned for Oct. 20 after testnet experience. Nov. 5 is the target, but only if that decision goes ahead.

Nothing's final yet.

Getting out, and what it exposes

Zallet's migration documentation excludes Sprout spending keys and funds from its import process and tells users to keep their original wallet.dat. The Argos recovery tool documents a route for holders with a legacy wallet file or standalone Sprout spending keys. With only a key, recovery may require reconstructing the extra data needed to build a valid spend. For a full-block scan, Argos estimates roughly 280 GB of transfer and potentially days of processing, while keeping less than 500 MB on disk.

According to its documentation, Argos's Sprout sweeps land in Sapling, a newer shielded pool, even when a Unified Address is supplied. That has privacy implications. ZIP 308's migration design says Sprout-to-Sapling value passes through public pool accounting, which exposes the amount without requiring a transparent address. Its scheme coordinates timing and randomizes amounts to reduce linkability, and ZIP 2003 warns that a short or poorly coordinated exit period can make distinctive amounts and timing easier to tie to holders.