Zcash Draft Upgrade Could Strand 22,309 ZEC in Sprout Pool

A draft rule for Zcash’s next network upgrade would cut off spending from the legacy Sprout pool, leaving its remaining funds inaccessible if the change takes effect on mainnet. The proposal targets the transaction format Sprout requires, so control of a private key would not provide a way around the rule.

The proposed NU7 rules would make all version 4 transactions invalid. Sprout transfers use version 4, while version 5 and version 6 transactions do not support the pool, leaving no supported post-activation transaction format for Sprout spending. The restriction would also catch version 4 transactions unrelated to Sprout, not only withdrawals from the pool.

The Sprout pool held 22,309.39145128 ZEC at block height 3,522,228 in a snapshot updated Sunday, Oct. 18, at 11:28 a.m. ET (15:28 UTC). That is the recorded pool balance ahead of NU7’s scheduled mainnet decision and target activation.

Under the proposed rule, any Sprout balance remaining after activation would stay issued and count toward Zcash’s supply calculations. The funds would not be burned, even though the upgraded network would no longer accept a supported spending transaction from the pool. The coins’ status in supply calculations would remain separate from a holder’s ability to authorize a transfer. A later protocol change could offer a retrieval method, but none is specified, and spending may never be restored.

Sprout was Zcash’s first shielded protocol. The Canopy upgrade stopped new value from entering the pool but left funds already there spendable. NU7’s proposed rule would end that remaining ability to move Sprout balances through version 4 transactions.

A migration procedure allows Sprout funds to move into Sapling, another shielded pool. The total amount leaving Sprout is visible in public pool accounting. The migration process uses staggered timing and varied transfer amounts to make individual transfers harder to link to holders.

NU7 activated on public testnet Oct. 4 at block height 4,465,026. TokenPost previously covered the testnet rollout and its 25-second block target. The mainnet rules remain in draft form, with a decision on activation and block height scheduled for Tuesday, Oct. 20. Nov. 5 is the listed target activation date, contingent on that decision.