MongoDB 3.1.8 has been released as a development release and is not intended for production use. The 3.1 series will evolve into 3.2, which will be suitable for production. This release includes several new features and fixes, including support for filtered partial indexes, improved index access statistics, and a built-in diagnostic data capture facility. Additionally, it addresses performance issues, such as a 30% regression on simple insert workloads on primary servers. The release also includes bug fixes and enhancements to existing functionality.