At Notion we are building a productivity suite used by more than 100 million people worldwide. At its core is a document editor with content organized in 'blocks' that can be split, merged and moved around.

To properly support real-time collaboration, as well as enable our offline editing feature, we needed to introduce conflict resolution. In this talk I'll discuss how we achieved this by implementing a CRDT (conflict-free replicated data type), some unique challenges we faced given our block model, and how we did this at scale.