Mina’s Mesa upgrade halted transaction processing for about eight hours on September 3 as the layer-1 blockchain moved its mainnet to the Mesa release. Exchanges suspended MINA deposits and withdrawals from the 10:00 UTC transaction cutoff until the Mesa network became operational, although each exchange controls when transfers resume. For five hours, upgraded block producers continued producing empty blocks for 100 slots; block production then stopped at 15:00 UTC for roughly three hours. The official runbook marks the transaction cutoff, empty-block period, halt, Mesa package release at 16:30 UTC and first Mesa slot at 18:00 UTC as completed, while archive-node and manual node upgrades remained in progress this morning. Mesa reduces slot times from three minutes to 90 seconds and temporarily limits zkApp transactions to 12 per block after stress tests found memory spikes when developers tested removing the soft limit. Deployed zkApps must be rebuilt with o1js 3.0 and receive new on-chain verification keys because Mesa changes protocol constants and circuit constraints. Until a compatible key is recorded, proof-authorized activity remains paused, although the deployed contract itself has not permanently failed. Mina’s migration path allows proof and impossible permission settings to fall back temporarily to signature authorization, except that accounts set to impossible remain locked. After a successful key update, the transaction version advances and the original verification-key permissions return. The fallback has no fixed deadline and remains active until the zkApp updates its key. The material also references XRPL’s May 27 upgrade as an example of how validators and markets manage a blockchain upgrade.