Zcash's NU7 Upgrade Will Lock Remaining Sprout Funds, With About $16 Million Reported

By Matthew Brienen

Published: 2026-11-05T15:00:00+00:00

An old pool faces a spending cutoff

Zcash's NU7 upgrade is set to make funds remaining in Sprout, its oldest shielded pool, unspendable under the new network rules. CoinDesk reported about 12,226 ZEC remained early November 5, worth roughly $16 million using a price of $1,300 per coin.

That is a dated balance estimate, not a confirmed final amount frozen. Further withdrawals before activation would reduce it, and the dollar value moves with ZEC's market price. CoinDesk reported the pool had held roughly 22,263 ZEC a week earlier, with most of the intervening reduction occurring on Sunday.

The cutoff is associated with mainnet block 3,543,405. CoinDesk estimated activation near 9:30 p.m. Eastern on November 5, while stressing that mining speed could shift the timing. A projected clock time should not be treated as a guaranteed deadline.

Why a valid private key will not be enough

ZIP 2003, the specification for retiring version-4 transactions, explains the mechanism. Sprout spending depends on that format. Once the network rejects it, possession of the correct private key cannot make a Sprout transaction valid under the new rules.

The proposal does not burn or unissue those coins. It leaves open the theoretical possibility of a future mechanism restoring access, while explicitly warning that spending may never be re-enabled. Holders therefore cannot assume a later recovery upgrade will arrive.

This is a change to transaction validity at the protocol level. It differs from a custodian temporarily disabling its withdrawal button: the restriction applies when the network checks the transaction itself. The distinction explains how an owner can retain proof of control while losing the ability to move a balance.

The format change reaches beyond Sprout

NU7's deployment specification says the version-4 prohibition also covers transparent-only and Sapling transactions constructed in that format. Newer version-5 and version-6 formats remain available, but Sprout has no supported replacement format after activation.

For other affected transactions, rebuilding them in a supported format may be possible. Simply signing the same invalid version-4 transaction again does not resolve the problem. Saved and offline-signed transactions also need activation checks, according to the specification.

The upgrade documentation separately warns that unsupported nodes may continue following pre-NU7 rules. That creates a software-readiness issue for operators alongside the balance-access issue for Sprout owners. A wallet displaying funds and a node accepting the current network's rules are different pieces of the same payment workflow.

Why developers are retiring the machinery

ZIP 2003 describes a maintenance burden from retaining obsolete Sprout components in live transaction-validation paths. The old system adds complexity and potential denial-of-service exposure despite limited use. Sapling and Orchard introduced newer privacy designs with substantial improvements.

Retiring old code can simplify what nodes must validate, but the cost is concrete for anyone with value still dependent on that code. The published aggregate balance cannot identify its owners or establish how much belongs to people who have lost their keys. It therefore cannot show how much is still practically recoverable before the cutoff.

The unanswered recovery question matters more than a headline about supply disappearing. Coins remaining in Sprout continue to count as issued under the specification. Treating them as formally burned would misdescribe the change and imply a supply adjustment the proposal does not make.

Faster blocks are another part of NU7

NU7 also reduces target block spacing from 75 seconds to 25 seconds. Its deployment specification pairs that increased frequency with limits intended to bound validation and shielded synchronization work. A shorter target interval concerns the expected wait between blocks; individual blocks still arrive at variable times.

For this story, the decisive observations are the chain reaching the activation height and the Sprout balance remaining then. The approximately $16 million figure describes the earlier snapshot. Confirmation of the final inaccessible amount requires a balance measured at the cutoff.