MongoDB 4.4 introduces "user-driven engineering" with new features including Union aggregation pipeline stage, custom aggregation expressions, connection monitoring and pooling, global read and write concerns, and improved MongoDB Query Language (MQL) with simplified syntax for searching strings and evaluating array elements. The release also includes enhancements to the MongoDB Rust Driver and Swift Driver, providing support for async programming and a universal programming experience. With these features, developers can build more efficient, scalable, and secure applications, while reducing the amount of data they need to pull back from the database, delivering higher performance to their users.