The MongoDB Connector for Apache Kafka version 1.9 introduces several key features, including support for pre and post document states, which allows for retrieving the before and after state of an entire document. This enables more accurate change event data to be included in the change stream event. Additionally, a new parameter called `startup.mode` has been added, allowing users to start processing data at a specific point in time or copy existing data first. The connector also now reports MongoDB errors to the dead letter queue, and changes behavior on inferring schema for arrays with different data type values. These updates aim to improve the accuracy and reliability of the connector's operations.