Zcash NU7 Upgrade Could Freeze 22,309 ZEC Left in the Sprout Pool

Update 00:04 UTC: In September, Aurora Intents handled more than $19 million through 1,718 transactions in a ZEC-denominated zkSNARKs auction, showing substantial demand for cross-chain paths into the coin.

22,309 ZEC Exposed to the Sprout Freeze

Anyone still holding ZEC in the protocol's first privacy pool is now working against a hard deadline. The warning turns a routine upgrade into a migration problem for every legacy wallet still in use. On-chain data counted about 22,309 ZEC left in the Sprout pool as of October 18, and the pending NU7 network upgrade is built in a way that would leave those coins unspendable after activation, even for holders who still control their private keys. The mechanism is Zcash's ZIP 2003, the improvement proposal bundled into NU7, which withdraws support for version 4 transactions. Sprout balances can only move through that legacy format, while the newer version 5 and version 6 formats that remain valid after NU7 do not handle Sprout transfers at all. Once the upgrade goes live, a coin sitting in Sprout can no longer be converted into a transaction the network will accept, so withdrawals and transfers to fresh addresses both fail regardless of key ownership. That last part is the unusual one: on most networks losing access to coins means losing the key, but here the key survives and the coins still stop moving.

Sprout dates back to the 2016 launch and the trusted setup performed for the original Zcash ceremony, making it the network's oldest shielded pool. It shares parts of its cryptography with the later Sapling pool but requires its own verification structure, a separate validation path that has weighed on network operations for years. Policy has moved in steps: ZIP 211 already stopped new funds from entering Sprout, and ZIP 2003 closes the exit as well. Zooko Wilcox, who co-founded the project, said on X that users should move any Sprout balance to another address before NU7 activates. He cautioned that recovering some holdings needs additional data, which can stretch the withdrawal into a lengthy process.

November 5 Activation Target

The timetable is set. A final decision on NU7's mainnet activation is due on October 20, and the conditional target date for applying the upgrade is November 5, which leaves Sprout holders a narrow window to act once that decision lands. NU7 is not only a removal: it also shortens Zcash's block time from 75 seconds to 25 seconds, speeding transaction confirmations across the network, and it adjusts the pace of new ZEC issuance while keeping the existing halving schedule intact. The package is framed around long-term operational efficiency, trimming the verification work node operators carry for a pool with a separate validation structure. If the October 20 decision confirms activation, wallet developers and node operators have a little over two weeks to ship version 5 and version 6 support, the formats every post-upgrade transaction must use. The market view around the upgrade is that these changes lower the network's running costs over time, with the caveat that unmigrated Sprout balances face restricted movement after the cutoff. Price action has run hot this month, which is why the freeze question reaches beyond archives and long-dormant wallets. Our earlier coverage followed ZEC's rebound from $1,077 to test the $1,229–$1,288 band, then a stretch of holding near $1,124 ahead of the October 28 Fed meeting. Speculation about the coin's trajectory has run alongside the technical work, including cofounder Eli Ben-Sasson's $2,000 target for 2026. Shielded-pool flows already draw close scrutiny: wallets linked to the Bitget hack moved 2,746 ZEC into the Ironwood shielded pool, a case that showed how closely Zcash's pool-level accounting gets watched. A pool that becomes unusable is a different kind of event, one measured in inaccessible balances rather than in flows.

Our reading is that NU7 amounts to protocol hygiene rather than a market event, and the price impact should stay muted while the operational risk concentrates in one specific group. About 22,309 ZEC is small against ZEC's circulating supply, but the cutoff is absolute: coins that fail to migrate become inaccessible, not merely delayed, because no supported transaction format can express a Sprout spend. Zcash technical analysis this month has centered on price bands, yet the binding number for these holders is a date, November 5. The party that has not moved yet is the legacy wallet holder, and for that group the workable paths are a migration to a modern shielded address or a deposit address at a crypto exchange, both of which require action before activation.

Separate work on the protocol's privacy side has also surfaced. The team behind Zakura, a newer release of Zcash's node software, published an engineering proposal that would give every ZEC swap made through NEAR Intents its own viewing key, so a refund address posted on NEAR's public chain could not, if cracked by a future quantum computer running Shor's algorithm, expose the rest of a user's payment history. Spending keys stay with the main account, and a private information retrieval database would let a wallet locate its refunds without revealing which addresses it is asking about. Zakura says compatible software wallets, including Vizor, could ship the open-source feature within weeks, with hardware wallets waiting on firmware support, ahead of the January target Zcash developers set for quantum-resistant payments.

The proposal, published on Zakura's engineering page, spells out the mechanics behind that quantum worry: when a user swaps ZEC for USDC through NEAR Intents, the service posts a refund address on NEAR's public chain, and that address is derived from the wallet's viewing key through elliptic curve cryptography. Shor's algorithm, first described in 1994, is the method a sufficiently capable quantum computer would use to reverse that derivation, and Zakura's writeup cites Google's Willow chip, which the company says recently produced core components needed for this type of attack. Because a single Zcash wallet's addresses typically share one viewing key, a cracked refund address would let an attacker link every incoming payment, including amounts and encrypted memo contents, to the same account. Zakura frames the per-swap key design as damage control: funds would stay safe, but a quantum compromise would be confined to a single transaction instead of the full payment history.

The NEAR Intents angle behind Zakura's proposal is not hypothetical, according to new reporting on the team's plan. In September, Aurora Intents handled more than $19 million through 1,718 transactions in a ZEC-denominated zkSNARKs auction, showing substantial demand for cross-chain paths into the coin. That volume is what makes the permanently posted refund addresses a live privacy concern, since multiple Zcash addresses currently share one underlying incoming viewing key that a capable quantum computer could in theory recover from a public address and use to link that account's payments. The one-key-per-swap design would confine any future compromise to a single exchange, while spending keys stay unchanged, so funds received via one-time addresses remain spendable from the same account without the burden of separate wallets.