Zcash Activates Critical Ironwood Upgrade Amidst Rapid User Migration

Zcash recently activated its Ironwood upgrade, also known as NU6.3, on July 28, 2026, at block height 3,428,143.

The upgrade replaced Orchard, the network's main privacy pool, with a new pool called Ironwood due to a bug discovered in Orchard's zero-knowledge proof circuit by Shielded Labs researcher Taylor Hornby on May 29, 2026.

The 'infinity' bug could have allowed attackers to mint counterfeit ZEC without leaving a public trace, but fortunately, there is no evidence it was exploited. Still, the uncertainty led developers to build and ship a replacement shielded pool rather than patching Orchard.

Ironwood has been gaining users rapidly since its activation, with over 1.2 million ZEC moved into the new pool in just three weeks. The migration is voluntary, but it's one-way, meaning coins can only be withdrawn from Orchard through a turnstile that caps withdrawals at verifiable deposits.