Bitcoin Core 30.3 fixes an issue that caused the chainstate database to repeatedly rewrite large portions of itself. According to the maintainers, the behaviour produced excessive disk activity during ordinary operation.
The release also contains changes to validation, networking and transaction-handling code. Its change list identifies the individual contributions, allowing a reader to follow an item back to the underlying development discussion.
This maintenance update belongs to the 30.x release series. It should be read alongside that series’ compatibility notes, rather than treated as a description of every version of Bitcoin software. The source page contains the full notes and links to the project’s distribution channels.