The MongoDB Java Driver 3.0 introduces significant changes to its design and architecture, aiming to improve performance and simplify the API. The new features include pluggable codecs, predictable cluster management, and additional connection pool settings. Deprecation of certain methods and classes is also planned for future releases. An alpha version of the driver is available for testing in a development environment, but it's not recommended for production use yet. The driver's architecture is designed to be backwards compatible with the existing API, allowing for a smooth transition from the 2.x driver to the new 3.0 version.