MongoDB 3.1.6 has been released as a development release and is not intended for production use. This release includes several user-facing features such as aggregation stage random document sampling, bitwise query operators, improved performance under high thread counts, and compact 2dsphere geo index formats. Additionally, the release addresses various issues including oplog performance degradation over time, mongodump single collection output issues, and keyfile support for encrypted storage engine functionality. The MongoDB team encourages users to report any issues encountered with this release.