Zcash Ironwood Upgrade Activates at Block 3,428,143, Replacing Vulnerable Orchard Pool

The Zcash Ironwood upgrade activated at block height 3,428,143 as part of the NU6.3 hard fork, replacing the Orchard shielded pool after researchers discovered an "infinity" bug in late May that posed a theoretical risk of undetectable counterfeit ZEC creation. Zooko Wilcox, Shielded Labs co-founder, led the strategic decision to scrap and rebuild Orchard entirely rather than rely solely on patching, resulting in a 60-day coordinated development effort across multiple organizations including Project Tachyon and the Zcash Foundation.

A machine-checked mathematical proof consisting of more than 2,700 theorems formally verifies that Ironwood cannot create undetectable counterfeit ZEC under its design assumptions. According to Zcash's migration tracker, approximately 40,207 ZEC have moved to Ironwood since activation, while roughly 3.6 million ZEC remain in Orchard, which now operates in exit-only mode. The upgrade also establishes Zebra as the required node implementation, ending support for legacy zcashd software.