Zcash has set a firm date for its next network upgrade: the Ironwood hard fork will activate at block height 3,428,143 — roughly 8 a.m. EST on July 28. The announcement from core developer Sean Bowe confirms a one-week delay from the originally planned July 21 rollout and says all major ecosystem players are committed to activating NU6.3 at that height.
Why Ironwood matters
- Ironwood was proposed in response to a serious bug discovered in Zcash’s Orchard shielded pool — the privacy-focused transaction system used for shielded ZEC transfers. The so-called “infinity” bug could, in theory, have allowed an attacker to mint unlimited counterfeit ZEC.
- Shielded Labs, which disclosed the issue, said it found no evidence the flaw had been exploited. Developers issued emergency fixes, temporarily disabled Orchard transactions, and deployed the NU6.2 hard fork on June 3 to patch the underlying vulnerability and restore the pool.
- When Ironwood activates, the existing Orchard pool will stop accepting new activity and funds will be migrated into a newly created private pool. Coins leaving Orchard must pass through an accounting checkpoint before entering Ironwood — a mechanism Shielded Labs says should reveal any anomalous coin creation. That means users migrating funds effectively force any hypothetical counterfeiter to either move fake coins and risk exposure or abandon them.
Operational friction and timing
- Some ecosystem participants — exchanges, mining pools, and wallet providers — raised concerns about the speed of the transition. Many were also swapping out the long-running zcashd client for the new Z3 stack (Zebra, Zaino, and Zallet), which created preparation pressure. Shielded Labs briefly floated delaying Ironwood, but Bowe’s announcement confirms the upgrade will go ahead on July 28.
Market and supply context
- The public disclosure of the Orchard vulnerability on June 3 hit sentiment hard: ZEC briefly plunged about 50%, from $602.68 to $299.25. The token has since recovered some ground and was trading around $492.61 at the time of reporting.
- Separately, Zcash hit a supply milestone this week. A post from ruZCASH showed circulating supply reached 16,806,723 ZEC — more than 80% of the 21 million maximum supply (roughly four-fifths mined).
Bottom line
Ironwood’s activation will close the current Orchard pool and route migratory activity through checkpoints intended to surface any evidence of counterfeit coins. With major organizations committed to the NU6.3 activation and emergency fixes already deployed, the network is moving toward a controlled transition — even as operators race to finish upgrades to the Z3 stack ahead of the July 28 switch.
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