This a stable release.
https://github.com/anza-xyz/agave/blob/v4.0/CHANGELOG.md
What's Changed
- v4.0: Drop current channel version test (backport of #12662) by @mergify[bot] in #12663
- v4.0: Freeze cargo-build-sbf version by @levsha in #12656
- v4.0: freeze spl-token-cli version by @levsha in #12657
- v4.0: Bank::get_slot_history() is fallible (backport of #12598) by @mergify[bot] in #12629
- v4.0: Fix secondary index memory (backport of #12726) by @mergify[bot] in #12741
- v4.0: ci: Specify user-agent for crates.io curl (backport of #12825) by @mergify[bot] in #12835
- Bump version to 4.0.1 by @github-actions[bot] in #12841
Full Changelog: v4.0.0...v4.0.1