Jeff Carpenter, author of "Cassandra: The Definitive Guide," is working on the third edition of the book to keep up with the evolving Cassandra database system. The new edition will cover updates from version 4.0, including performance improvements, virtual tables for easier monitoring and management, transient replication, and enhanced security features. Additionally, the book will discuss running Cassandra in Docker, using Kubernetes operators, and migrating from legacy relational databases to Cassandra. The third edition is set to release on April 21, 2020, with a free copy available for a limited time through DataStax's sponsorship.