This release addresses a performance regression introduced in #1661 -- thanks to all who reported this quickly: @chlunde, @dethi, @aaronbee @tsuna @kakkoyun 💪🏽. This patch release also fixes the iOS build.

We will be hardening the release process even further (#1759, #1761) to prevent this in future, sorry for the inconvenience!

The high concurrency optimization is planned to be eventually reintroduced, however in a much safer manner, potentially in a separate API.

• [BUGFIX] prometheus: Revert of Inc, Add and Observe cumulative metric CAS optimizations (#1661), causing regressions on low concurrency cases #1757
• [BUGFIX] prometheus: Fix GOOS=ios build, broken due to process_collector_* wrong build tags. #1758

All commits

• Revert "exponential backoff for CAS operations on floats" and cut 1.21.1 by @bwplotka in https://github.com/prometheus/client_golang/pull/1757
• Fix ios build for 1.21.1 by @bwplotka in https://github.com/prometheus/client_golang/pull/1758

Full Changelog: https://github.com/prometheus/client_golang/compare/v1.21.0...v1.21.1