Flask End of Life - Dates and Lifecycle

Flask has been part of the Python web ecosystem since 2010, built on Werkzeug and Jinja to offer a minimal core with extensions handling everything else. It's one of the most widely used Python web frameworks, valued for giving developers control over structure rather than imposing one.

Flask Lifecycle Explained

Flask has no formal, published end of life policy, and its own maintainers have confirmed this directly in response to user questions. As maintainer davidism put it, "the latest feature branch gets bug fixes... when a new feature release is made, that will become the new supported branch." Maintainer tachyondecay added explicitly that Flask does not use semantic versioning in the way that implies long-term support for older lines, only the most recently released version is supported at any given time.

In practice, this means every prior release becomes unsupported the moment a new one ships, security fixes included. Flask's own guidance to application developers is to pin dependencies deliberately, using standard Python packaging tools, rather than relying on the framework itself to maintain older branches. New releases also periodically drop support for older Python versions in step with Python's own end of life schedule.

A February 2022 incident illustrates why this matters in practice, not just in theory. Flask versions before 2.0 specified only a lower bound on their itsdangerous dependency (itsdangerous >= 0.24), with no upper limit. When itsdangerous 2.1.0 shipped, it removed code that older Flask versions relied on, and installing Flask 1.1.2 or similar would silently pull in the newest itsdangerous and crash with an ImportError, even for teams who had deliberately stayed on an older Flask version. Maintainer davidism's response was direct: the affected versions were unsupported, and the real fix was to pin the full dependency tree with a tool like pip-tools rather than expect Flask to keep old branches compatible with newer releases of its own dependencies.