eteq · Feb 25, 2021 · Oct 16, 2020 · Oct 16, 2020 · Oct 16, 2020 · Oct 16, 2020
diff --git a/APE10.rst b/APE10.rst
@@ -270,3 +270,6 @@ After v3.0, a decision was made to adjust the release calendar by +3 months.
 The table above has been updated appropriately.  v3.3 was also removed on this
 basis, as the timing for the end of Python 2.x support is better aligned with an
 end-of-2019 4.0 release.
+
+This APE is superceded by `APE18 <APE18.rst>`_, which contains the version
+support plan for versions from 4.0 on.
diff --git a/APE18.rst b/APE18.rst
@@ -0,0 +1,70 @@
+Adopt NEP 29 for CPython and Numpy Version Support
+--------------------------------------------------
+
+author: Stuart Mumford and Thomas Robitaille
+
+date-created: 2020 October 16
+
+date-last-revised: 2021 February 25
+
+type: Standard Track
+
+status: Accepted
+
+
+Abstract
+--------
+
+APE 10 previously determined supported CPython versions, and provided a list up to the 4.0 release.
+Since APE 10 was written the wider scientific Python community have written and largely adopted `NEP 29`_ as a policy for supported versions of both CPython and Numpy.
+This APE proposes that Astropy adopt this policy following other projects in the scientific ecosystem.
+
+
+Detailed description
+--------------------
+
+This APE fully adopts `NEP 29`_ for both CPython and Numpy versions for the core astropy package, and it supersedes APE 10 wherever there is a conflict between that APE and this APE or `NEP 29`_.
+
+This APE will not replicate the content of `NEP 29`_, and the full text of `NEP 29`_ is adopted via this APE.
+In addition to the content of `NEP 29`_, the APE also extends the numpy policy to all of the core package dependencies.
+This leads to the following support policy for dependencies of the core package.
+
+Astropy core will support:
+
+* All minor versions of Python released 42 months prior to a non-bugfix, and at minimum the two latest minor versions.
+* All minor versions of numpy released in the 24 months prior to a non-bugfix, and at minimum the last three minor versions.
+* Versions of other runtime dependencies released 24 months prior to a non-bugfix release.
+
-
+
+Note that, as stated in `NEP 29`_, these timelines all apply for the versions
+set at the time of the non-bugfix release.  This means that the full
+support timelines for LTS versions of astropy are 66 and 48 months for Python
+and numpy, respectively.
+
-
+set at the time of the non-bugfix release.  So for example the v4.0 release, an
+LTS, would support Python 3.6 (released 23 mo earlier), and would continue to
+support it until the end of the LTS window (24 mo after the 4.0 release).
+Whereas 4.2, planned for late 2020, would  unambiguously only support 3.7 (as
+its full lifetime falls within the 3.7 window).
-
+
+Note that, as stated in `NEP 29`_, these timelines all apply for the versions
+set at the time of the non-bugfix release.  This means that the full
+support timelines for LTS versions of astropy are 66 and 48 months for Python
+and numpy, respectively.
+
-
+set at the time of the non-bugfix release.  So for example the v4.0 release, an
+LTS, would support Python 3.6 (released 23 mo earlier), and would continue to
+support it until the end of the LTS window (24 mo after the 4.0 release).
+Whereas 4.2, planned for late 2020, would  unambiguously only support 3.7 (as
+its full lifetime falls within the 3.7 window).
+These versions of the dependencies are to be supported for bugfix lifetime of the given astropy version.
+
+This version support policy allows, at the discretion of the maintainers, to adopt the supported version of the next release in situations where it is judged to be valuable.
+For example, this could be done in the case of an important change in numpy or a change over date very close to the release.
+
+
+Implementation
+--------------
+
+Some initial work has been done in `#10900 <https://github.com/astropy/astropy/pull/10900>`__ on bumping the minimum Python version in the core astropy package to Python 3.7+.
+
+The release calendar for the astropy core package will be updated over time to include the minimum Python and Numpy version for upcoming releases.
+Backward compatibility
+----------------------
+
+The version schedule here is more rapid than that proposed in APE 10, however, this allows the core library to adopt modern features, and reduces burden on maintainers.
+In addition to this, aligning ourselves with other projects in the ecosystem is consistent and prevents potential minimum version conflicts.
+See the text of `NEP 29`_ for further justification.
+
+This APE fully replaces APE10 where they are in conflict.
+
+Alternatives
+------------
+
+See `NEP 29`_.
+
+Decision rationale
+------------------
+
+After discussion and some revision in the PR, there was broad support and no
+objections to adopting this plan.
+
+.. _NEP 29: https://numpy.org/neps/nep-0029-deprecation_policy.html