Zcash Sets July 28 Ironwood Fork to Seal Orchard Upgrade

Ironwood hard fork aims to resolve Orchard supply uncertainty

Zcash has scheduled the Ironwood upgrade (NU6.3) to activate at block 3,428,143 on July 28. The hard fork will retire the current Orchard shielded pool and deploy a new, corrected shielded circuit. The primary objective is not to retroactively identify any counterfeit ZEC, but to close the old pool and prevent any hypothetical excess hidden supply from leaving the shielded environment and entering wider circulation.

Activation details and what changes

Block activation and new shielded pool

Ironwood is set to trigger at block 3,428,143. Once activated, the protocol will disable sending and receiving inside the legacy Orchard pool and instantiate a new shielded pool using the patched cryptographic circuit. This migration completes the network’s earlier cryptographic fixes and formalizes a controlled path forward for shielded transactions.

Turnstile mechanism and supply controls

Instead of attempting to trace or freeze individual coins, Ironwood introduces a turnstile constraint on withdrawals from the old Orchard pool. The turnstile only allows ZEC to leave the legacy pool up to the amount that legitimately entered it, so node operators can verify that the circulating ZEC supply respects the protocol’s monetary rules. The upgrade therefore focuses on limiting the risk of excess value escaping a privacy-preserving pool, rather than proving whether a past exploit occurred.

Technical background: the Orchard flaw and prior mitigation

Security researcher Taylor Hornby discovered the Orchard vulnerability on May 29 during an audit of Zcash’s shielded system. The flaw could have made it possible to create counterfeit ZEC inside Orchard without a transparent public trail, because Orchard’s privacy features obscure transaction details.

After the discovery, the development team temporarily disabled some Orchard activity and deployed corrective cryptography in the NU6.2 update. No evidence to date points to unauthorized value creation, but the nature of shielded pools means that developers and users cannot independently prove with absolute certainty that no counterfeit ZEC was ever created. Ironwood is designed to address that residual supply uncertainty by sealing the old pool and limiting withdrawal pathways.

Impact on wallets, exchanges, and users

Service pauses and migration requirements

General users do not need to take immediate action before July 28. However, exchanges, custodial wallets, and other service providers are likely to pause deposits, withdrawals, or related services temporarily while they upgrade software and add migration tooling. Wallets will need updates to support moving funds into the new shielded pool; funds stored in wallets that have not integrated these migration tools could be temporarily inaccessible.

Migration from legacy clients

The Ironwood activation also follows Zcash’s ongoing migration away from the legacy zcashd client. Providers still in the process of moving to supported clients may need extra time to complete upgrades and resume full service for users.

Security audits, AI-assisted review, and formal verification

The Orchard incident prompted broader security hardening across the Zcash ecosystem. An AI-assisted code review using Anthropic’s Mythos system reportedly found no additional high-severity vulnerabilities following the initial disclosure. In parallel, Zcash developers are pursuing independent audits and formal verification of the revised cryptographic circuits to reduce the chance of another hidden counterfeiting risk and to strengthen assurances around supply correctness.

Ironwood’s approach puts emphasis on protocol-level proofs and system checks rather than transaction-level tracing. Developers hope that formal verification, combined with external audits, will deliver stronger guarantees for privacy-focused features while preserving monetary integrity.

What users and node operators should know

• Users: No immediate action is required, but check announcements from your wallet provider or exchange and expect short maintenance windows around July 28. If you use shielded addresses, confirm that your wallet will support the migration into the new Orchard pool.
• Node operators: Upgrade nodes and validate new client releases so you can enforce the turnstile constraints and help the network confirm that circulating ZEC adheres to protocol rules.
• Service providers: Coordinate testing and deployment timelines to reduce downtime and communicate clearly with customers about deposit and withdrawal windows.

Bottom line

Ironwood is a carefully targeted hard fork intended to neutralize an unresolved supply risk introduced by an Orchard cryptography flaw. While it cannot retroactively identify or freeze specific counterfeit coins, the upgrade seals the vulnerable pool and uses a turnstile mechanism to prevent any hypothetical excess from entering circulation. Combined with audits and formal verification efforts, Ironwood is a pragmatic step toward restoring greater confidence in Zcash’s privacy-preserving ledger and supply integrity.