Zcash NU7 Upgrade Set to Freeze $16 Million in Sprout Pool Coins

Zcash will render roughly 12,224 ZEC — worth $15 million to $16 million at recent prices — permanently unspendable when its NU7 network upgrade activates at block 3,543,405, expected Thursday evening in the United States. The coins sit in Sprout, the privacy coin's original shielded pool, and the deadline depends on block production speed, not a fixed clock time. As of publication, the chain had reached block 3,543,027.

ZecStats, which tracks the data, states the consequence plainly: "NU7 (block 3,543,405) makes v4 transactions invalid, so what remains in Sprout is unspendable: frozen, not burned."

Why is Zcash shutting down Sprout?

Zcash launched in 2016 with Sprout as its first privacy system. Unlike Bitcoin, where transaction amounts and addresses are visible on-chain, Zcash uses zero-knowledge proofs to validate transactions without revealing their details. Sprout introduced that technology, but the project has since shipped better alternatives: Sapling, Orchard, and Ironwood. Sprout has been closed to new deposits for years, though existing holders could still withdraw.

NU7 eliminates version-4 transactions, the only format capable of moving coins out of Sprout. After activation, any transaction using that format becomes invalid under the network's technical specification.

The rationale is operational. Supporting obsolete technology adds complexity and potential security vulnerabilities. Sprout's original privacy system demanded substantial computing resources, and its aging transaction-verification mechanisms carry risks the development team wants gone.

Are the coins burned or frozen?

Frozen, technically. The coins are not destroyed — they will still count toward Zcash's circulating issuance calculations. A future upgrade could theoretically restore access, but the specification explicitly warns that spending those funds may never be re-enabled. The team has shown no interest in reversing the change.

There's also a measurement problem. The blockchain cannot reveal who owns the remaining Sprout balance, so nobody knows how much belongs to active users versus how much is already lost with abandoned private keys.

What do holders need to do?

Legacy holders face the exposure. Anyone with ZEC still in Sprout must move it through a compatible withdrawal mechanism before activation or risk losing access indefinitely. Sprout addresses begin with "zc," which helps users spot old wallet records. Holders using modern supported wallets don't need to migrate anything, though keeping wallet software updated remains standard practice.

The stakes are real even for people who did everything right: owners who still hold their passwords and private keys will lose access anyway if they miss the block deadline.

What else changes in NU7?

The upgrade isn't only about retiring Sprout. Zcash's target block interval falls from 75 seconds to 25 seconds, meaning transactions receive their first confirmation roughly three times faster, according to the Zcash Foundation. For everyday users and merchants, that shortens the practical wait before a payment counts as confirmed.

The move also strips deprecated technology from the codebase, reducing the maintenance burden and attack surface the old pool imposed on every node operator.

Once block 3,543,405 lands, the freeze takes effect under the new rules — and any holder still watching from the sidelines will have run out of blocks to act on.