Release notes of the 3.13-rc.1 release:

The 3.13.0-rc.0 release was only partially successful due to the migration from NPM to PNPM and subsequent CI issues, so most of the changes in this release candidate are CI/build-related. The only user-facing change is:

• [CHANGE] UI: Third-party npm dependency licenses are now embedded in the Prometheus binary and served at /assets/third-party-licenses.txt, replacing the npm_licenses.tar.bz2 archive previously shipped in release tarballs and container images. #18997

Release notes of the 3.13-rc.0 release, as it was not published in partial state:

• [SECURITY] UI: Bump sanitize-html to fix a cross-site scripting vulnerability (CVE-2026-44990). #18697
• [CHANGE] API: Use SHA-256 instead of SHA-1 to generate rule group pagination tokens. #18927
• [CHANGE] HTTP clients: Credentials (Authorization header, basic auth, bearer token, OAuth2, configured headers) are no longer forwarded when following a redirect to a different host; affects scraping, remote read/write, alerting, and service discovery. Via prometheus/common v0.69.0 (CVE-2025-4673 CVE-2023-45289). #18949
• [CHANGE] promtool: Relative file paths in the file passed to --http.config.file are now resolved relative to that config file's directory instead of its parent directory. Via prometheus/common v0.69.0. #18949
• [CHANGE] PromQL: Rename the min() and max() duration-expression functions (experimental feature flag experimental-duration-expr) to min_of() and max_of() to avoid confusion with the min and max aggregate operators. #18687
• [FEATURE] API: Add experimental search endpoints to search metric names, label names, and label values. #18573
• [FEATURE] Discovery/AWS: Add ability to filter RDS instances. #18859
• [FEATURE] PromQL: Add min_of(a, b) and max_of(a, b) scalar experimental functions, returning the smaller or larger of two scalar values. #18687
• [FEATURE] PromQL: Add support for smoothed/anchored rate with native histograms. #18564
• [FEATURE] PromQL: Expose per-query samplesRead (and samplesReadPerStep with stats=all and the promql-per-step-stats feature flag) in the query stats response, and add the prometheus_engine_query_samples_read_total engine counter. samplesRead reflects storage I/O distinct from totalQueryableSamples, which counts samples loaded into the evaluator (and so over-counts when a sample is reused across multiple range-vector windows). #18081
• [FEATURE] Scrape: Add __convert_classic_histograms_to_nhcb__ internal label to allow per-target override of convert_classic_histograms_to_nhcb scrape configuration via relabeling. #18840
• [FEATURE] TSDB: Add storage.tsdb.chunk_encoding.floats configuration field to select float chunk encoding (xor or xor2) at runtime, independently of the --enable-feature=xor2-encoding flag. #18769
• [FEATURE] remote_write: Add Certificate support for ingesting data into an Azure Monitor Workspace. #18217
• [FEATURE] Scrape: Add __always_scrape_classic_histograms__ and __scrape_native_histograms__ internal labels to allow per-target override of the always_scrape_classic_histograms and scrape_native_histograms scrape configuration via relabeling. #18929
• [ENHANCEMENT] Release: Container images are now also published to the GitHub Container Registry (ghcr.io). #18791
• [ENHANCEMENT] PromQL: Prettify fill_left(x) fill_right(x) as fill(x) when both fill values are equal. #18851
• [ENHANCEMENT] UI: Improve autocompletion after closing a function bracket. #18894
• [PERF] Labels: Add case-insensitive prefix matching to speed up evaluation of long case-insensitive regular expressions (up to ~2x faster). #18540
• [PERF] TSDB: Reduce per-sample overhead in chunk population, speeding up affected queries by ~12-15% in benchmarks. #18699
• [PERF] TSDB: Eliminate unnecessary heap allocations in the V2 histogram WAL decoder, reducing allocations by up to 50% and memory by up to 10% for deployments using native histograms with created-timestamp storage enabled (--enable-feature=created-timestamp-zero-ingestion). #18813
• [BUGFIX] Discovery/AWS: Fix failure when processing an AWS RDS cluster without instances. #18845
• [BUGFIX] Fix race condition in initTime that could cause ErrOutOfBounds. #18629
• [BUGFIX] PromQL: A range query whose end was not aligned to step caused subqueries inside it to evaluate past the parent's last actual step, inflating peakSamples in the query stats and against the query.max-samples limit, and wasting storage I/O reading samples that were never used in the result. #18081
• [BUGFIX] PromQL: A range query containing an at-modifier-unsafe function over a range-vector with an @ modifier (e.g. predict_linear(metric[60s] @ T, X)) silently under-counted totalQueryableSamples for steps after step 0. #18081
• [BUGFIX] PromQL: Fix fill_left/fill_right producing missing samples in range queries when using group_left/group_right. #18850
• [BUGFIX] PromQL: Fix for resets() and changes() in anchored range extenders with histograms. #18906
• [BUGFIX] PromQL: Fix panic on 1[5m] smoothed and similar expressions when extended range selectors are enabled. #18764
• [BUGFIX] PromQL: Fix panic when a smoothed instant vector selector produces no samples for a series. #18943
• [BUGFIX] PromQL: Fix panic when using a parenthesised plain number as an offset (e.g. foo offset -(5)). #18768
• [BUGFIX] promtool: Fix panic when parsing exposition text containing empty braces {}. Via prometheus/common v0.69.0. #18949
• [BUGFIX] Promtool: Fix check healthy and check ready when --url ends with a trailing slash. #18854
• [BUGFIX] Rules: Close PromQL query after each rule evaluation to ensure resources are released. #18733
• [BUGFIX] Scaleway SD: Resolve VPC/IPAM-only instances that have no legacy private_ip or public_ip field, but do have private NICs attached. #18772
• [BUGFIX] TSDB: Do not leak head series when an integer histogram append is rejected (e.g. out-of-order). #18838
• [BUGFIX] UI: Escape label values offered by PromQL autocomplete. #18658
• [BUGFIX] TSDB: Fix chunk snapshot encoding for EncXOR2 chunks, preventing corruption on TSDB restart when EncXOR2-encoded series were present. #18739
• [BUGFIX] TSDB: Store a millisecond timestamp (not a WAL segment number) in walExpiries when a series is evicted via CompactStaleHead/CompactSelectedSeries, so the series's label record is correctly retained in the next WAL checkpoint and replays cleanly. #18847
• [BUGFIX] TSDB: Prevent loss of samples at the chunk-range boundary when CompactSelectedSeries (and CompactStaleHead) evict the series — the per-slice compaction loop now runs one more iteration so the boundary timestamp is captured in a block before the in-memory copy is removed. #18849