diff --git a/HACKING.rst b/HACKING.rst
index bb55ac5..1c084f8 100644
--- a/HACKING.rst
+++ b/HACKING.rst
@@ -419,3 +419,34 @@
 tested is considered stable and adheres to the OpenStack API stability
 guidelines. If an API is still considered experimental or in development then
 it should not be tested by Tempest until it is considered stable.
+
+Stable Support Policy
+---------------------
+
+Since the `Extended Maintenance policy`_ for stable branches was adopted
+OpenStack projects will keep stable branches around after a "stable" or
+"maintained" period for a phase of indeterminate length called "Extended
+Maintenance". Prior to this resolution Tempest supported all stable branches
+which were supported upstream. This policy does not scale under the new model
+as Tempest would be responsible for gating proposed changes against an ever
+increasing number of branches. Therefore due to resource constraints, Tempest
+will only provide support for branches in the "Maintained" phase from the
+documented `Support Phases`_. When a branch moves from the *Maintained* to the
+*Extended Maintenance* phase, Tempest will tag the removal of support for that
+branch as it has in the past when a branch goes end of life.
+
+The expectation for *Extended Maintenance* phase branches is that they will continue
+running Tempest during that phase of support. Since the REST APIs are stable
+interfaces across release boundaries, branches in these phases should run
+Tempest from master as long as possible. But, because we won't be actively
+testing branches in these phases, it's possible that we'll introduce changes to
+Tempest on master which will break support on *Extended Maintenance* phase
+branches. When this happens the expectation for those branches is to either
+switch to running Tempest from a tag with support for the branch, or blacklist
+a newly introduced test (if that is the cause of the issue). Tempest will not
+be creating stable branches to support *Extended Maintenance* phase branches, as
+the burden is on the *Extended Maintenance* phase branche maintainers, not the Tempest
+project, to support that branch.
+
+.. _Extended Maintenance policy: https://governance.openstack.org/tc/resolutions/20180301-stable-branch-eol.html
+.. _Support Phases: https://docs.openstack.org/project-team-guide/stable-branches.html#maintenance-phases