Zcash NU7 to Freeze $16 Million in Oldest Privacy Pool

Zcash's next network upgrade will close the door on the network's oldest privacy pool. NU7 makes version 4 transactions invalid, and a version 4 transaction is the only way to reach Sprout, the shielded pool Zcash launched in 2016. About 12,227 ZEC sits there today, worth roughly $16 million.

The coins are not burned, and no one is seizing private keys. They stay counted in Zcash's total supply. But once NU7 is live, any attempt to move them will fail.

• NU7 disables version 4 transactions, while versions 5 and 6 stay valid (ZIP 259).
• ZecStats puts the Sprout pool at 12,227 ZEC, down 45.1% from 22,263 ZEC a week earlier.
• Zcash's total supply is 17.02 million ZEC, and ZEC traded at $1,293 in the same table.
• At that price, the remaining Sprout balance is worth about $16 million.

What NU7 Changes on Zcash

NU7 does more than retire old transactions. It cuts the block target spacing from 75 seconds to 25 seconds, adds per-pool and global limits on shielded actions, and introduces the Network Sustainability Mechanism. It also removes 60% of transaction fees from circulation.

Why Version 4 Transactions Matter

Sprout is the original shielded pool, the part of the ledger where transaction details stay private. Only version 4 transactions can reach it. ZIP 2003, the proposal behind the change, is direct about the reach: disallowing v4 affects every workflow that creates v4 transactions, and Sprout transfers are only one of them. The v4 block also covers transparent-only and Sapling transactions.

What Happens to the Stranded Sprout Coins

ZIP 2003 says the plan does not unissue, burn, or make Sprout funds permanently unavailable. That leaves a narrow path open. The community could re-enable v4 transactions, or build another facility to retrieve the funds. The same ZIP warns that spending Sprout funds may never be re-enabled.

Sending into Sprout was already blocked. Four years before this proposal, the Canopy upgrade changed consensus rules to prohibit sending funds into the pool, so the balance could only shrink.

When NU7 Takes Effect

NU7 is scheduled for block 3,543,405. That is the point where version 4 transactions stop being valid. If you are checking old wallet records, Sprout addresses begin with "zc".

What the Sprout Balance Shows and Hides

ZecStats computes supply and pool balances from a full Zebra node it runs, not a third-party API, and calls the figures consensus-verified. That makes the 45% weekly fall a real movement of coins rather than an estimate.

What it cannot show is who holds them, or how much belongs to wallets whose keys are lost. A pool balance is a single number, and it does not come with a holder list.

The nearest dated event is block 3,543,405. When it arrives, the Sprout coins stay counted in supply but stop moving, and any return depends on a future upgrade that ZIP 2003 says may never come.