Zcash has activated its Ironwood upgrade (formally NU6.3) at block 3,428,143, effectively sealing the previous "Orchard" shielded pool. The Orchard pool holds approximately 3.66 million ZEC, valued at about $1.7 billion. This upgrade was prompted by the discovery of a counterfeiting bug in Orchard's proof circuit, which could have allowed attackers to mint undetected ZEC for four years since May 2022.

The Ironwood upgrade introduces a new shielded pool, starting from zero tokens. To mitigate the risk from the old bug, coins can only exit the Orchard pool via a "turnstile" rule, which caps total withdrawals at the amount verifiably deposited, ensuring any potential counterfeit coins remain trapped. The new pool also features quantum-resistant cryptography and formal verification of its proof circuit to enhance security. ZEC traded near $463 ahead of the switch.