Prometheus v3.15.0 released on 25-09-2026
Prometheus v3.15.0 is out now. It delivers PromQL correctness and reliability fixes, TSDB and storage stability and performance improvements, plus scraping, discovery and runtime changes that reduce query errors and improve on-disk safety.
See the project’s GitHub release notes for full details, tests and upgrade guidance.
What’s in this release
- PromQL correctness fixes — a range-query/subquery alignment bug is fixed so subqueries no longer evaluate past a parent’s last step, plus many fixes to info() enrichment, @/offset handling, FastRegexMatcher false-positives and range-selector/offset validation.
- TSDB and storage improvements — XOR2 float chunk encoding stabilised and recommended via storage.tsdb.chunk_encoding.floats: xor2, fast-path XOR decompression for faster queries, new head metrics and fixes to prevent dropped samples, deadlocks and WAL-related panics.
- Scraping, discovery and UI changes — support for scraping via Unix domain sockets and the OM2.0 scrape format, optional zstd-compressed scrape responses behind a feature flag, faster shutdown of scrape pools and improved native-histogram UI formatting.
Upgrade notes
- Deprecated flag: –log.level is deprecated. Use runtime.log_level to supply the default level and change log level on configuration reload.
- Storage and rollback: the xor2-encoding flag is deprecated — enable XOR2 via storage.tsdb.chunk_encoding.floats: xor2 only after confirming any direct-TSDB readers (for example Thanos sidecar) support XOR2; Agent mode now ignores unknown WAL record types to ease rollbacks.
Share any problems or wins after upgrading on the project’s issue tracker or community channels — feedback helps catch edge cases.
