diff --git a/doc/source/tenants.rst b/doc/source/tenants.rst
index a82031366a..1b0469ea6c 100644
--- a/doc/source/tenants.rst
+++ b/doc/source/tenants.rst
@@ -232,6 +232,45 @@ configuration. Some examples of tenant definitions are:
             It will not exclude a branch which already matched
             *include-branches*.
 
+         .. attr:: always-dynamic-branches
+
+            A list of regular expressions matching branches which
+            should be treated as if every change newly proposes
+            dynamic Zuul configuration.  In other words, the only time
+            Zuul will realize any configuration related to these
+            branches is during the time it is running jobs for a
+            proposed change.
+
+            This is potentially useful for situations with large
+            numbers of rarely used feature branches, but comes at the
+            cost of a significant reduction in Zuul features for these
+            branches.
+
+            Every regular expression listed here will also implicitly
+            be included in *exclude-branches*, therefore Zuul will not
+            load any static in-repo configuration from this branch.
+            These branches will not be available for use in overriding
+            checkouts of repos, nor will they be included in the git
+            repos that Zuul prepares for *required-projects* (unless
+            there is a change in the dependency tree for this branch).
+
+            In particular, this means that the only jobs which can be
+            specified for these branches are pre-merge and gating jobs
+            (such as :term:`check` and :term:`gate`).  No post-merge
+            or periodic jobs will run for these branches.
+
+            Using this setting also incurs additional processing for
+            each change submitted for these branches as Zuul must
+            recalculate the configuration layout it uses for such a
+            change as if it included a change to a ``zuul.yaml`` file,
+            even if the change does not alter the configuration).
+
+            With all these caveats in mind, this can be useful for
+            repos with large numbers of rarely used branches as it
+            allows Zuul to omit their configuration in most
+            circumstances and only calculate the configuration of a
+            single additional branch when it is used.
+
          .. attr:: extra-config-paths
 
             Normally Zuul loads in-repo configuration from the first
diff --git a/releasenotes/notes/always-dynamic-dce165ca8b6e212f.yaml b/releasenotes/notes/always-dynamic-dce165ca8b6e212f.yaml
new file mode 100644
index 0000000000..0d0fe82260
--- /dev/null
+++ b/releasenotes/notes/always-dynamic-dce165ca8b6e212f.yaml
@@ -0,0 +1,10 @@
+---
+features:
+  - |
+    Added a new
+    :attr:`tenant.untrusted-projects.<project>.always-dynamic-branches`
+    tenant project configuration option.  This may be used to specify
+    branches from which Zuul should never load static configuration
+    and instead treat every change as if it newly proposed dynamic
+    configuration.  This is potentially useful for large numbers of
+    rarely-used feature branches.
diff --git a/tests/fixtures/config/dynamic-only-project/dynamic.yaml b/tests/fixtures/config/dynamic-only-project/dynamic.yaml
new file mode 100644
index 0000000000..d11451181b
--- /dev/null
+++ b/tests/fixtures/config/dynamic-only-project/dynamic.yaml
@@ -0,0 +1,10 @@
+- tenant:
+    name: tenant-one
+    source:
+      gerrit:
+        config-projects:
+          - common-config
+        untrusted-projects:
+          - org/project:
+              always-dynamic-branches:
+                - "^feature/.*"
diff --git a/tests/fixtures/config/dynamic-only-project/exclude.yaml b/tests/fixtures/config/dynamic-only-project/exclude.yaml
new file mode 100644
index 0000000000..58a0b03f10
--- /dev/null
+++ b/tests/fixtures/config/dynamic-only-project/exclude.yaml
@@ -0,0 +1,10 @@
+- tenant:
+    name: tenant-one
+    source:
+      gerrit:
+        config-projects:
+          - common-config
+        untrusted-projects:
+          - org/project:
+              exclude-branches:
+                - "^feature/.*"
diff --git a/tests/fixtures/config/dynamic-only-project/git/common-config/playbooks/run.yaml b/tests/fixtures/config/dynamic-only-project/git/common-config/playbooks/run.yaml
new file mode 100644
index 0000000000..ed97d539c0
--- /dev/null
+++ b/tests/fixtures/config/dynamic-only-project/git/common-config/playbooks/run.yaml
@@ -0,0 +1 @@
+---
diff --git a/tests/fixtures/config/dynamic-only-project/git/common-config/zuul.yaml b/tests/fixtures/config/dynamic-only-project/git/common-config/zuul.yaml
new file mode 100644
index 0000000000..331abc54e3
--- /dev/null
+++ b/tests/fixtures/config/dynamic-only-project/git/common-config/zuul.yaml
@@ -0,0 +1,67 @@
+- pipeline:
+    name: check
+    manager: independent
+    trigger:
+      gerrit:
+        - event: patchset-created
+        - event: comment-added
+          comment: '^(Patch Set [0-9]+:\n\n)?(?i:recheck)$'
+    success:
+      gerrit:
+        Verified: 1
+    failure:
+      gerrit:
+        Verified: -1
+
+- pipeline:
+    name: gate
+    manager: dependent
+    success-message: Build succeeded (gate).
+    trigger:
+      gerrit:
+        - event: comment-added
+          approval:
+            - Approved: 1
+    success:
+      gerrit:
+        Verified: 2
+        submit: true
+    failure:
+      gerrit:
+        Verified: -2
+    start:
+      gerrit:
+        Verified: 0
+    precedence: high
+
+- pipeline:
+    name: post
+    manager: independent
+    trigger:
+      gerrit:
+        - event: ref-updated
+          ref: ^(?!refs/).*$
+    precedence: low
+
+- job:
+    name: base
+    parent: null
+    run: playbooks/run.yaml
+
+- job:
+    name: central-test
+
+- job:
+    name: central-post
+
+- project:
+    name: "^org/project.*"
+    check:
+      jobs:
+        - central-test
+    gate:
+      jobs:
+        - central-test
+    post:
+      jobs:
+        - central-post
diff --git a/tests/fixtures/config/dynamic-only-project/git/org_project/README b/tests/fixtures/config/dynamic-only-project/git/org_project/README
new file mode 100644
index 0000000000..9daeafb986
--- /dev/null
+++ b/tests/fixtures/config/dynamic-only-project/git/org_project/README
@@ -0,0 +1 @@
+test
diff --git a/tests/fixtures/config/dynamic-only-project/git/org_project/zuul.yaml b/tests/fixtures/config/dynamic-only-project/git/org_project/zuul.yaml
new file mode 100644
index 0000000000..9712c08280
--- /dev/null
+++ b/tests/fixtures/config/dynamic-only-project/git/org_project/zuul.yaml
@@ -0,0 +1,17 @@
+- job:
+    name: project-test
+
+# Note: this job is not expected to run
+- job:
+    name: project-post
+
+- project:
+    check:
+      jobs:
+        - project-test
+    gate:
+      jobs:
+        - project-test
+    post:
+      jobs:
+        - project-post
diff --git a/tests/fixtures/config/dynamic-only-project/include.yaml b/tests/fixtures/config/dynamic-only-project/include.yaml
new file mode 100644
index 0000000000..315eccc547
--- /dev/null
+++ b/tests/fixtures/config/dynamic-only-project/include.yaml
@@ -0,0 +1,11 @@
+- tenant:
+    name: tenant-one
+    source:
+      gerrit:
+        config-projects:
+          - common-config
+        untrusted-projects:
+          - org/project:
+              include-branches:
+                - master
+                - stable
diff --git a/tests/unit/test_v3.py b/tests/unit/test_v3.py
index 37a9c092fa..24943b4ecb 100644
--- a/tests/unit/test_v3.py
+++ b/tests/unit/test_v3.py
@@ -8048,3 +8048,120 @@ class TestConnectionVars(AnsibleZuulTestCase):
         # job_output = self._get_file(job, 'work/logs/job-output.txt')
         # self.log.debug(job_output)
         # self.assertNotIn("/bin/du", job_output)
+
+
+class IncludeBranchesTestCase(ZuulTestCase):
+    def _test_include_branches(self, history1, history2, history3, history4):
+        self.create_branch('org/project', 'stable')
+        self.create_branch('org/project', 'feature/foo')
+        self.fake_gerrit.addEvent(
+            self.fake_gerrit.getFakeBranchCreatedEvent(
+                'org/project', 'stable'))
+        self.fake_gerrit.addEvent(
+            self.fake_gerrit.getFakeBranchCreatedEvent(
+                'org/project', 'feature/foo'))
+        self.waitUntilSettled()
+
+        # Test the jobs on the master branch.
+        A = self.fake_gerrit.addFakeChange('org/project', 'master', 'A')
+        self.fake_gerrit.addEvent(A.getPatchsetCreatedEvent(1))
+        self.waitUntilSettled()
+
+        self.assertHistory(history1, ordered=False)
+
+        # Test the jobs on the excluded feature branch.
+        B = self.fake_gerrit.addFakeChange('org/project', 'feature/foo', 'A')
+        self.fake_gerrit.addEvent(B.getPatchsetCreatedEvent(1))
+        self.waitUntilSettled()
+
+        self.assertHistory(history1 + history2, ordered=False)
+
+        # Test in-repo config proposed on the excluded feature branch.
+        conf = textwrap.dedent(
+            """
+            - job:
+                name: project-dynamic
+
+            - project:
+                check:
+                  jobs:
+                    - project-dynamic
+            """)
+        file_dict = {'zuul.yaml': conf}
+        C = self.fake_gerrit.addFakeChange('org/project', 'feature/foo', 'A',
+                                           files=file_dict)
+        self.fake_gerrit.addEvent(C.getPatchsetCreatedEvent(1))
+        self.waitUntilSettled()
+
+        self.assertHistory(history1 + history2 + history3, ordered=False)
+
+        # Merge a change to the excluded feature branch.
+        B.addApproval('Code-Review', 2)
+        self.fake_gerrit.addEvent(B.addApproval('Approved', 1))
+        self.waitUntilSettled()
+        self.assertEqual(B.data['status'], 'MERGED')
+        self.assertHistory(history1 + history2 + history3 + history4,
+                           ordered=False)
+
+
+class TestIncludeBranchesProject(IncludeBranchesTestCase):
+    tenant_config_file = 'config/dynamic-only-project/include.yaml'
+
+    def test_include_branches(self):
+        history1 = [
+            dict(name='central-test', result='SUCCESS', changes='1,1'),
+            dict(name='project-test', result='SUCCESS', changes='1,1'),
+        ]
+        history2 = [
+            dict(name='central-test', result='SUCCESS', changes='2,1'),
+        ]
+        history3 = [
+            dict(name='central-test', result='SUCCESS', changes='3,1'),
+        ]
+        history4 = [
+            dict(name='central-test', result='SUCCESS', changes='2,1'),
+        ]
+        self._test_include_branches(history1, history2, history3, history4)
+
+
+class TestExcludeBranchesProject(IncludeBranchesTestCase):
+    tenant_config_file = 'config/dynamic-only-project/exclude.yaml'
+
+    def test_exclude_branches(self):
+        history1 = [
+            dict(name='central-test', result='SUCCESS', changes='1,1'),
+            dict(name='project-test', result='SUCCESS', changes='1,1'),
+        ]
+        history2 = [
+            dict(name='central-test', result='SUCCESS', changes='2,1'),
+        ]
+        history3 = [
+            dict(name='central-test', result='SUCCESS', changes='3,1'),
+        ]
+        history4 = [
+            dict(name='central-test', result='SUCCESS', changes='2,1'),
+        ]
+        self._test_include_branches(history1, history2, history3, history4)
+
+
+class TestDynamicBranchesProject(IncludeBranchesTestCase):
+    tenant_config_file = 'config/dynamic-only-project/dynamic.yaml'
+
+    def test_dynamic_branches(self):
+        history1 = [
+            dict(name='central-test', result='SUCCESS', changes='1,1'),
+            dict(name='project-test', result='SUCCESS', changes='1,1'),
+        ]
+        history2 = [
+            dict(name='central-test', result='SUCCESS', changes='2,1'),
+            dict(name='project-test', result='SUCCESS', changes='2,1'),
+        ]
+        history3 = [
+            dict(name='central-test', result='SUCCESS', changes='3,1'),
+            dict(name='project-dynamic', result='SUCCESS', changes='3,1'),
+        ]
+        history4 = [
+            dict(name='central-test', result='SUCCESS', changes='2,1'),
+            dict(name='project-test', result='SUCCESS', changes='2,1'),
+        ]
+        self._test_include_branches(history1, history2, history3, history4)
diff --git a/zuul/configloader.py b/zuul/configloader.py
index b83a87acb2..70eb8d35ce 100644
--- a/zuul/configloader.py
+++ b/zuul/configloader.py
@@ -1518,6 +1518,7 @@ class TenantParser(object):
         'load-branch': str,
         'include-branches': to_list(str),
         'exclude-branches': to_list(str),
+        'always-dynamic-branches': to_list(str),
         'allow-circular-dependencies': bool,
     }}
 
@@ -1700,11 +1701,18 @@ class TenantParser(object):
             min_ltime = -1
         branches = sorted(tpc.project.source.getProjectBranches(
             tpc.project, tenant, min_ltime))
-        branches = [b for b in branches if tpc.includesBranch(b)]
         if 'master' in branches:
             branches.remove('master')
             branches = ['master'] + branches
-        tpc.branches = branches
+        static_branches = []
+        always_dynamic_branches = []
+        for b in branches:
+            if tpc.includesBranch(b):
+                static_branches.append(b)
+            elif tpc.isAlwaysDynamicBranch(b):
+                always_dynamic_branches.append(b)
+        tpc.branches = static_branches
+        tpc.dynamic_branches = always_dynamic_branches
 
     def _loadProjectKeys(self, connection_name, project):
         project.private_secrets_key, project.public_secrets_key = (
@@ -1730,6 +1738,7 @@ class TenantParser(object):
             project_exclude_unprotected_branches = None
             project_include_branches = None
             project_exclude_branches = None
+            project_always_dynamic_branches = None
             project_load_branch = None
         else:
             project_name = list(conf.keys())[0]
@@ -1754,12 +1763,28 @@ class TenantParser(object):
                 project_include_branches = [
                     re.compile(b) for b in as_list(project_include_branches)
                 ]
-            project_exclude_branches = conf[project_name].get(
+            exclude_branches = conf[project_name].get(
                 'exclude-branches', None)
-            if project_exclude_branches is not None:
+            if exclude_branches is not None:
                 project_exclude_branches = [
-                    re.compile(b) for b in as_list(project_exclude_branches)
+                    re.compile(b) for b in as_list(exclude_branches)
                 ]
+            else:
+                project_exclude_branches = None
+            always_dynamic_branches = conf[project_name].get(
+                'always-dynamic-branches', None)
+            if always_dynamic_branches is not None:
+                if project_exclude_branches is None:
+                    project_exclude_branches = []
+                    exclude_branches = []
+                project_always_dynamic_branches = []
+                for b in always_dynamic_branches:
+                    rb = re.compile(b)
+                    if b not in exclude_branches:
+                        project_exclude_branches.append(rb)
+                    project_always_dynamic_branches.append(rb)
+            else:
+                project_always_dynamic_branches = None
             if conf[project_name].get('extra-config-paths') is not None:
                 extra_config_paths = as_list(
                     conf[project_name]['extra-config-paths'])
@@ -1777,6 +1802,8 @@ class TenantParser(object):
             project_exclude_unprotected_branches
         tenant_project_config.include_branches = project_include_branches
         tenant_project_config.exclude_branches = project_exclude_branches
+        tenant_project_config.always_dynamic_branches = \
+            project_always_dynamic_branches
         tenant_project_config.extra_config_files = extra_config_files
         tenant_project_config.extra_config_dirs = extra_config_dirs
         tenant_project_config.load_branch = project_load_branch
@@ -2577,7 +2604,8 @@ class ConfigLoader(object):
         else:
             # Use the cached branch list; since this is a dynamic
             # reconfiguration there should not be any branch changes.
-            branches = tenant.getProjectBranches(project.canonical_name)
+            branches = tenant.getProjectBranches(project.canonical_name,
+                                                 include_always_dynamic=True)
 
         for branch in branches:
             fns1 = []
diff --git a/zuul/model.py b/zuul/model.py
index 50482138db..aaa324251f 100644
--- a/zuul/model.py
+++ b/zuul/model.py
@@ -5387,6 +5387,9 @@ class Ref(object):
         tpc = tenant.project_configs.get(self.project.canonical_name)
         if tpc is None:
             return False
+        if hasattr(self, 'branch'):
+            if tpc.isAlwaysDynamicBranch(self.branch):
+                return True
         if self.files is None:
             # If self.files is None we don't know if this change updates the
             # config so assume it does as this is a safe default if we don't
@@ -6309,11 +6312,13 @@ class TenantProjectConfig(object):
         self.load_classes = set()
         self.shadow_projects = set()
         self.branches = []
+        self.dynamic_branches = []
         # The tenant's default setting of exclude_unprotected_branches will
         # be overridden by this one if not None.
         self.exclude_unprotected_branches = None
         self.include_branches = None
         self.exclude_branches = None
+        self.always_dynamic_branches = None
         self.parsed_branch_config = {}  # branch -> ParsedConfig
         # The list of paths to look for extra zuul config files
         self.extra_config_files = ()
@@ -6322,6 +6327,13 @@ class TenantProjectConfig(object):
         # Load config from a different branch if this is a config project
         self.load_branch = None
 
+    def isAlwaysDynamicBranch(self, branch):
+        if self.always_dynamic_branches is None:
+            return False
+        for r in self.always_dynamic_branches:
+            if r.fullmatch(branch):
+                return True
+
     def includesBranch(self, branch):
         if self.include_branches is not None:
             included = False
@@ -7574,16 +7586,21 @@ class Tenant(object):
                                 (project,))
         return result
 
-    def getProjectBranches(self, project_canonical_name):
+    def getProjectBranches(self, project_canonical_name,
+                           include_always_dynamic=False):
         """Return a project's branches (filtered by this tenant config)
 
         :arg str project_canonical: The project's canonical name.
+        :arg bool include_always_dynamic: Whether to include
+             always-dynamic-branches
 
         :returns: A list of branch names.
         :rtype: [str]
 
         """
         tpc = self.project_configs[project_canonical_name]
+        if include_always_dynamic:
+            return tpc.branches + tpc.dynamic_branches
         return tpc.branches
 
     def getExcludeUnprotectedBranches(self, project):