API stability

From its first release, cryptography has had a strong API stability policy.

What does this policy cover?

This policy includes any API or behavior that is documented in this documentation.

What does “stable” mean?

  • Public APIs will not be removed or renamed without providing a compatibility alias.

  • The behavior of existing APIs will not change.

What doesn’t this policy cover?

  • We may add new features, things like the result of dir(obj)) or the contents of obj.__dict__ may change.

  • Objects are not guaranteed to be pickleable, and pickled objects from one version of cryptography may not be loadable in future versions.

  • Unless otherwise documented, types in cryptography are not intended to be sub-classed, and we do not guarantee that behavior with respect to sub-classes will be stable.

  • Development versions of cryptography. Before a feature is in a release, it is not covered by this policy and may change.


One exception to our API stability policy is for security. We will violate this policy as necessary in order to resolve a security issue or harden cryptography against a possible attack.


Version 35.0.0+

Beginning with release 35.0.0 cryptography uses a Firefox-inspired version scheme.

Given a version cryptography X.Y.Z,

  • X indicates the major version number. This is incremented on any feature release.

  • Y is always 0.

  • Z is an integer that is incremented for minor backward-compatible releases (such as fixing security issues or correcting regressions in a major release).

This scheme is compatible with SemVer, though many major releases will not include any backwards-incompatible changes.


From time to time we will want to change the behavior of an API or remove it entirely. In that case, here’s how the process will work:

  • In cryptography X.0.0 the feature exists.

  • In cryptography (X + 1).0.0 using that feature will emit a CryptographyDeprecationWarning (base class UserWarning).

  • In cryptography (X + 2).0.0 using that feature will emit a CryptographyDeprecationWarning.

  • In cryptography (X + 3).0.0 the feature will be removed or changed.

In short, code that runs without warnings will always continue to work for a period of two major releases.

From time to time, we may decide to deprecate an API that is particularly widely used. In these cases, we may decide to provide an extended deprecation period, at our discretion.

Previous Scheme

Before version 35.0.0 this project uses a custom versioning scheme as described below.

Given a version cryptography X.Y.Z,

  • X.Y is a decimal number that is incremented for potentially-backwards-incompatible releases.

    • This increases like a standard decimal. In other words, 0.9 is the ninth release, and 1.0 is the tenth (not 0.10). The dividing decimal point can effectively be ignored.

  • Z is an integer that is incremented for backward-compatible releases.