Meteor 3.5 Switches to MongoDB Change Streams, Boosting Capacity by 40%

Meteor 3.5, released on June 30, 2026, replaces the decade-old oplog tailing mechanism with MongoDB Change Streams as the default reactivity system. The key difference is that filtering now happens inside MongoDB itself, meaning the application only processes writes relevant to active publications rather than every database write. Benchmark tests showed the new driver handled 1,680 concurrent virtual users compared to 1,200 under oplog — a 40% increase — and crucially avoided the Out of Memory crashes that plagued high-traffic Meteor deployments. The change requires no modifications to application code, functioning as an internal engine swap rather than an API overhaul. Because fewer servers are needed to handle the same load, the upgrade also translates into reduced infrastructure costs for production teams.