Zcash NU7 upgrade could freeze about $15 million left in old Sprout pool

About 12,224 ZEC still sit in Sprout ahead of NU7

Zcash is preparing to shut down its oldest privacy technology, which could leave millions of dollars in cryptocurrency inaccessible to their owners. This could happen even if owners still have the passwords and private keys needed to access their wallets.

About 12,224 ZEC remain in Sprout, the cryptocurrency's original privacy pool, according to ZecStats data updated Thursday. At recent market prices, those holdings are worth roughly $15 million to $16 million.

The NU7 upgrade is scheduled for block 3,543,405, expected Thursday evening in the United States. The exact time depends on how fast the blockchain, which is a shared digital record of transactions, processes new blocks. At the time of publication, the latest block was 3,543,027.

Key numbers behind the freeze

• About 12,224 ZEC remain in Sprout, worth roughly $15 million to $16 million at recent prices.
• NU7 activates at block 3,543,405.
• After activation, version-4 transactions will be invalid, so what remains in Sprout will be unspendable.
• Zcash's target block interval will fall from 75 seconds to 25 seconds.

Why the old privacy pool is closing

Unlike Bitcoin, where transactions are generally visible to anyone examining the blockchain, Zcash allows users to conceal transaction amounts and the addresses involved. It does this with zero-knowledge proofs, a technology that can verify a transaction is valid without revealing its private details.

Sprout introduced this technology when Zcash launched in 2016. The team later introduced improved privacy systems, including Sapling, Orchard, and Ironwood. Sprout has been closed to new deposits for years, but existing holders could still withdraw their funds.

NU7 changes that by eliminating version-4 transactions, the only format capable of moving coins out of Sprout. ZecStats says: "NU7 (block 3,543,405) makes v4 transactions invalid, so what remains in Sprout is unspendable: frozen, not burned."

The decision addresses the problem of supporting obsolete technology. Develops say Sprout's original privacy system required substantial computing resources, and its outdated transaction-verification mechanisms create risks that developers want to eliminate.

What Sprout holders need to do before activation

Anyone whose ZEC remains in Sprout must move it through a compatible withdrawal mechanism before the upgrade activates, or risk losing access indefinitely.

Sprout addresses begin with "zc," which can help users recognize old wallet records. A wallet is software that holds cryptocurrency and private keys. Regular ZEC holders using modern supported wallets do not need to migrate their coins out of Sprout, although keeping wallet software updated remains important.

Developers have not technically destroyed the coins. They will continue counting toward Zcash's circulating issuance calculations.

What is still unclear about the remaining coins

The blockchain cannot reveal who owns the remaining Sprout balance. That means nobody knows how much belongs to active users and how much is already inaccessible because its owners lost their keys.

A future network upgrade could theoretically restore access, but that is not guaranteed. The team has not shown any interest in doing so, and the specification explicitly warns that spending those funds may never be re-enabled.

How NU7 changes transactions for other users

NU7 brings a benefit for other users, according to the Zcash Foundation. The target block interval falls from 75 seconds to 25 seconds, meaning transactions should receive their first confirmation approximately three times faster.

Sources

• Decrypt

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