Bitcoin Core 31.0 introduces a cluster-based design for its mempool, the local collection of transactions awaiting confirmation. The release notes explain that related transactions are considered as connected groups.
The change affects local policies used when preparing block templates, relaying transactions and handling replacements. The notes also describe a larger default database cache on machines where enough memory is detected, with a caution about systems whose detected memory exceeds their actual allowance.
Version 31.0 also places the 28.x series and older versions at end of life. These details belong to this release’s documentation; a version number alone does not explain compatibility. The official notes set out the changes that operators need to assess.