Zcash seals $1.7 billion shielded pool as Ironwood upgrade activates The upgrade retires Orchard, where a counterfeiting bug sat undetected for four years. Every coin inside now has to leave through a gate that caps withdrawals at verified deposits. - Zcash has activated its Ironwood (NU6.3) upgrade, sealing the Orchard shielded pool that held about 3.66 million ZEC and opening a new private pool that starts with zero coins. - A previously undisclosed bug in Orchard’s proof circuit could have allowed the creation of counterfeit ZEC without onchain traces, prompting the move to Ironwood and a turnstile mechanism that caps withdrawals to verifiable deposits. - Ironwood introduces quantum-resilient record-keeping and formally verified proof circuits, but the pace at which users voluntarily migrate funds from Orchard will determine how quickly Zcash’s private supply shifts to the new pool. Zcash activated its Ironwood upgrade at block 3,428,143 on Tuesday, sealing the so-called “shielded pool” that holds most of the network's private funds and opening a migration into a pool that starts from zero tokens. Ironwood, formally known as NU6.3, retired the previous pool known as Orchard, which holds about 3.66 million ZEC, worth roughly $1.7 billion at current prices. Ironwood held zero ZEC at activation, trackers showed. Every coin has to be moved across by its owner, and the only route out of Orchard is a turnstile — an accounting rule at the pool's boundary that caps total withdrawals at the amount verifiably deposited. Shielded pools are the private side of Zcash, where the amounts of coins and participants are hidden. A zero-knowledge proof provides evidence that the amount deposited is reflected publicly. On May 29, Shielded Labs researcher Taylor Hornby found that Orchard's proof circuit contained a bug that would let an attacker mint counterfeit ZEC, leaving no onchain trace. The