Experimental support forzstd on scrape was added, controlled by the requestAccept-Encoding header.
It was enabled by default since version 1.20, but now you need to add a blank import to enable it.
The decision to make it opt-in by default was originally made because the Go standard library was expected to have default zstd support added soon,
golang/go#62513 however, the work took longer than anticipated and it will be postponed to upcoming major Go versions.

e.g.:

import (  _"github.com/prometheus/client_golang/prometheus/promhttp/zstd")

[FEATURE] prometheus: Add new CollectorFunc utility#1724
[CHANGE] Minimum required Go version is now 1.22 (we also test client_golang against latest go version - 1.24)#1738
[FEATURE] api:WithLookbackDelta andWithStats options have been added to API client.#1743
[CHANGE]⚠️ promhttp: Isolate zstd support and klauspost/compress library use to promhttp/zstd package.#1765

All Changes

build(deps): bump golang.org/x/sys from 0.28.0 to 0.29.0 by@dependabot in#1720
build(deps): bump google.golang.org/protobuf from 1.36.1 to 1.36.3 by@dependabot in#1719
Update RELEASE.md by@bwplotka in#1721
chore(docs): Add links for the upstream PRs by@kakkoyun in#1722
Added tips on releasing client and checking with k8s. by@bwplotka in#1723
feat: Add new CollectorFunc utility by@Saumya40-codes in#1724
build(deps): bump google.golang.org/protobuf from 1.36.3 to 1.36.4 by@dependabot in#1725
build(deps): bump the github-actions group with 5 updates by@dependabot in#1726
Synchronize common files from prometheus/prometheus by@prombot in#1727
Synchronize common files from prometheus/prometheus by@prombot in#1731
build(deps): bump golang.org/x/sys from 0.29.0 to 0.30.0 by@dependabot in#1739
build(deps): bump google.golang.org/protobuf from 1.36.4 to 1.36.5 by@dependabot in#1740
Cleanup dependabot config by@SuperQ in#1741
Upgrade Golang version v1.24 by@dongjiang1989 in#1738
build(deps): bump the github-actions group with 2 updates by@dependabot in#1742
Merging 1.21 release back to main. by@bwplotka in#1744
Synchronize common files from prometheus/prometheus by@prombot in#1745
Add support for undocumented query options for API by@mahendrapaipuri in#1743
exp/api: Add experimental exp module; Add remote API with write client and handler. by@bwplotka in#1658
exp/api: Add accepted msg type validation to handler by@saswatamcode in#1750
build(deps): bump the github-actions group with 5 updates by@dependabot in#1751
build(deps): bump github.com/klauspost/compress from 1.17.11 to 1.18.0 by@dependabot in#1752
build(deps): bump github.com/google/go-cmp from 0.6.0 to 0.7.0 by@dependabot in#1753
exp: Reset snappy buf by@saswatamcode in#1756
Merge release 1.21.1 to main. by@bwplotka in#1762
exp: Add dependabot config by@saswatamcode in#1754
build(deps): bump peter-evans/create-pull-request from 7.0.7 to 7.0.8 in the github-actions group by@dependabot in#1764
promhttp: Isolate zstd support and klauspost/compress library use to promhttp/zstd package by@liggitt in#1765
Cut 1.22.0-rc.0 by@kakkoyun in#1768