Calendar versioning has a long history, and CalVer users can be found in all areas. This ever-growing, never-complete list of project names and example versions is open to expansion. To keep it useful, a listed project should be recognizable within its ecosystem and have either a public adoption announcement or a sustained calendar-versioned release history. For the order in which projects switched, see the timeline.

Schemes are written in the notation from the CalVer overview: M, D, and W are unpadded; 0M, 0D, and 0W are zero-padded; YY is the short year and 0Y the zero-padded one. See the overview for detailed case studies.

Operating systems and platforms

Whole systems have many parts and long support windows, which is where a date in the version pays off most.

Databases and infrastructure

Infrastructure software tends to publish support windows, and a calendar version lets operators read the window off the number.

See the NVIDIA case study for how one company ended up with both padding styles.

Languages and standards

Programming language standards are conventionally named for their year (YY/YYYY), and comprise some of the oldest notable usages of calendar versioning.

Python itself came close. PEP 2026 proposed calendar versioning for CPython (3.26 in 2026, 3.YY) in 2024. The Steering Council rejected it in early 2025 on a close vote, citing ecosystem churn rather than the idea itself.

Libraries

CalVer software libraries allow developers to evaluate their software freshness with just a glance at the dependency list.

Utilities and tools

Tools ship often and get installed everywhere, so the version people report in bug reports should say how old it is.

APIs and services

Versioned APIs pin a date, and the date tells both sides of the integration how far behind it is.

Stripe integrations pin a dated version, and since 2024 the twice-yearly breaking releases carry a plant name. Shopify cuts a version each quarter, supports each for at least twelve months with at least nine months of overlap, and echoes the version a request was served with in the X-Shopify-API-Version header.

Tooling

Implementations that compute, bump, or validate calendar versions. Notation compatibility with this site is noted where it matters.

• bumpver (Python CLI): pattern-based bumping for any language's version files, with the most complete calver.org token support. Its MM, DD, and WW are the pre-26.0 deprecated spellings of M, D, and W, with the same unpadded meaning.
• calver (setuptools plugin): derives a version from the build date via strftime. Used by PyPA's trove-classifiers.
• hatch-calver (Hatch plugin): date-derived versions for Hatch-built Python packages.
• node-calver (JavaScript): parse, validate, and increment calendar versions in Node.
• release-please (Google's release automation): a calendar versioning strategy is in review as of this writing.
• calver-adoption (agent skill): walks a coding agent through adopting CalVer in an existing project, from detecting the current version to cutting the first calendar release.

Other

If you know of a CalVer usage that does not fit into these categories, please submit it here.