Zcash will activate its Ironwood network upgrade, or NU6.3, on July 28, 2026 at block height 3,428,143, about a week later than originally scheduled. The upgrade is centered on fixing a major flaw previously disclosed in the Orchard shielded pool and restoring verifiable token supply through an on-chain migration.
Upgrade targets the Orchard shielded pool flaw
Ironwood follows a disclosure by the development team that the Orchard shielded pool, Zcash’s primary private transaction system, contained an “infinity” flaw. Shielded Labs said the defect could theoretically allow an attacker to mint an unlimited amount of counterfeit ZEC that would not be detectable. At the same time, it said there is currently no evidence that the vulnerability was exploited in the wild.
Because of Orchard’s privacy design, outside observers could not independently verify on-chain whether supply inside the pool had been inflated.
On-chain migration adds an accounting checkpoint
Ironwood’s approach is to require all funds leaving the Orchard pool to pass through an “accounting checkpoint.” That process is designed to reveal whether counterfeit ZEC had ever been minted in the past. After the migration is complete, any full node will be able to independently verify that no fake coins entered the new pool.
According to the report, this marks the first time since the flaw emerged that Zcash restores trustless supply verification at the protocol level.
Most holders do not need to act right away
Core developer Sean Bowe said all major organizations have committed to activating NU6.3 at block height 3,428,143, which is expected at around 8 a.m. U.S. Eastern Time on July 28. For most ZEC holders, no immediate action is expected to be necessary. Wallet providers are expected to offer one-click migration tools, and users will not need to replace their private keys.
Exchanges, mining pools, wallets and other infrastructure providers, however, will need to support the migration to the new pool.
Timeline concerns had focused on software migration
Shielded Labs had earlier raised concerns that operators were being asked not only to prepare for the new pool migration, but also to move away from the long-used zcashd software stack and adopt the new Z3 stack: Zebra, Zaino and Zallet. That led to concerns that the preparation window might be too short, and a delay had briefly been discussed. The upgrade has now been confirmed for the end of this month.
After the activation date was confirmed, ZEC rose about 13% over the past week.