Zcash developers have locked in the Ironwood network upgrade for activation tomorrow at block height 3,428,143, roughly 8 a.m. Eastern time. The change, formally known as NU6.3, creates a new shielded pool and forces remaining funds out of the older Orchard pool through a public accounting checkpoint.
The move follows the discovery in late May of a critical soundness flaw in Orchard that could have allowed an attacker to mint unlimited counterfeit ZEC without detection. The vulnerability sat in the code since Orchard launched in 2022.
An emergency fix known as NU6.2 closed the hole in early June. Because Orchard transactions hide amounts and owners, researchers could not prove whether anyone had exploited the bug before the patch.
Core developer Sean Bowe and teams at Shielded Labs and the Zcash Open Development Lab have said they found no evidence of actual counterfeiting, yet the uncertainty remained.
New pool and turnstile close the gap
In a July 10 release, Zcash Foundation described that Ironwood reuses the Orchard proof system and circuit but starts a fresh pool. Once the upgrade height is reached, wallets will route new shielded payments to Ironwood. The old Orchard pool will accept no new deposits or internal transfers.
Any remaining balance can leave only by passing through the network’s existing turnstile, which publicly records the exact amount exiting and entering. That rule prevents more ZEC from leaving the old pool than ever entered it.
Over time, the migration is expected to give node operators a clear, independent way to confirm the circulating supply has not been inflated.
The upgrade also introduces quantum-recoverable notes. If future quantum computers break today’s discrete-log assumptions, a recovery process can still reclaim Ironwood funds. As older pools lack that option, developers stress this is not full quantum resistance; broader post-quantum work remains scheduled for later upgrades.
With the upgrade going live, node operators must run software that supports the new rules before height 3,428,143 or risk falling onto a minority chain. Zebra 6.0.0 already includes full support.
Many wallets plan to prompt users holding Orchard balances to migrate with a single action while many exchanges and services may pause deposits or withdrawals briefly around the activation window while they confirm their systems.
As of Monday morning the chain sat more than 1,500 blocks short of the target. At current average block times the height is projected for mid-afternoon UTC on July 28. Trackers show roughly 3.76 million ZEC still sitting in Orchard, waiting to cross the turnstile once the gate opens.
Also read: Triple-A Hack Losses Reach $11.8M as Deposits Drained for 31 Hours
