TL;DR
- Zcash activated Ironwood at block 3,428,143, sealing Orchard to new deposits and opening a new shielded pool that began with zero ZEC.
- Orchard held about 3.66 million ZEC worth roughly $1.7 billion, while a turnstile now caps withdrawals at verified historical deposits.
- Ironwood adds quantum-resilient records and formal proof verification, but migration remains voluntary, leaving most private ZEC inside the retired Orchard pool until individual holders choose to move it.
Zcash activated its Ironwood upgrade, formally known as NU6.3, at block 3,428,143 on Tuesday, closing the Orchard shielded pool to new deposits and opening a fresh private pool with zero coins. Orchard held about 3.66 million ZEC, valued near $1.7 billion, making the transition unusually consequential for a privacy network. Ironwood forces Zcash to rebuild its shielded supply from a clean starting point. Every holder must voluntarily move funds, leaving the pace of migration dependent on users rather than an automatic protocol transfer. The retired pool can no longer accept deposits.
— Zcash Open Development Lab (@zodl_co) July 28, 2026
A turnstile contains uncertainty left by Orchard’s hidden flaw
The upgrade follows the discovery of a bug in Orchard’s proof circuit that could have allowed counterfeit ZEC to be created without leaving an onchain trace. Researcher Taylor Hornby identified the flaw on May 29, four years after Orchard launched. Developers patched it within days, but privacy itself created an impossible accounting problem. Nobody can prove that counterfeit coins were never created during the vulnerability window. Evidence suggests exploitation was unlikely because Orchard’s balance kept growing, even when selling during last year’s rally would have been profitable, yet absolute certainty remains unavailable. That ambiguity is precisely what made retirement necessary.
Ironwood addresses that uncertainty with a turnstile mechanism at Orchard’s boundary. Deposits into and withdrawals from shielded pools are publicly measurable even when internal transactions and participants remain hidden. The network therefore knows how much legitimate ZEC entered Orchard and will not permit more than that amount to leave. Any counterfeit coins that might exist are effectively trapped inside the retired pool. By publication time, approximately 1,500 ZEC had already migrated, while the remaining private supply still depended on individual holders choosing to complete the transition. That ceiling turns transparency into direct containment.
The new pool also introduces protections that Orchard lacked. Coin records are designed to remain recoverable if quantum computers eventually break today’s cryptography, while Ironwood’s proof circuit is undergoing formal verification to mathematically test its behavior across all possible cases. Zcash is pairing immediate containment with longer-term cryptographic resilience. ZEC traded near $463 before activation, down 8% for the day and 15% for the week, though still roughly ten times higher over the past year. The central question is now how quickly users move the remaining 3.66 million ZEC. Most private ZEC therefore remains inside Orchard.
