diff --git a/neutron_lib/api/definitions/__init__.py b/neutron_lib/api/definitions/__init__.py
index 1fbc15042..55df729a6 100644
--- a/neutron_lib/api/definitions/__init__.py
+++ b/neutron_lib/api/definitions/__init__.py
@@ -33,6 +33,7 @@ from neutron_lib.api.definitions import l2_adjacency
 from neutron_lib.api.definitions import l3
 from neutron_lib.api.definitions import l3_ext_gw_mode
 from neutron_lib.api.definitions import l3_ext_ha_mode
+from neutron_lib.api.definitions import l3_flavors
 from neutron_lib.api.definitions import logging
 from neutron_lib.api.definitions import logging_resource
 from neutron_lib.api.definitions import network
@@ -81,6 +82,7 @@ _ALL_API_DEFINITIONS = {
     l3,
     l3_ext_gw_mode,
     l3_ext_ha_mode,
+    l3_flavors,
     logging,
     logging_resource,
     network,
diff --git a/neutron_lib/api/definitions/l3_flavors.py b/neutron_lib/api/definitions/l3_flavors.py
new file mode 100644
index 000000000..6ef438107
--- /dev/null
+++ b/neutron_lib/api/definitions/l3_flavors.py
@@ -0,0 +1,41 @@
+# Licensed under the Apache License, Version 2.0 (the "License"); you may
+# not use this file except in compliance with the License. You may obtain
+# a copy of the License at
+#
+#      http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+# WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+# License for the specific language governing permissions and limitations
+# under the License.
+
+from neutron_lib.api.definitions import l3
+from neutron_lib import constants
+
+
+FLAVOR_ID = 'flavor_id'
+
+ALIAS = 'l3-flavors'
+IS_SHIM_EXTENSION = False
+IS_STANDARD_ATTR_EXTENSION = False
+NAME = 'Router Flavor Extension'
+API_PREFIX = ''
+DESCRIPTION = 'Flavor support for routers.'
+UPDATED_TIMESTAMP = '2016-05-17T00:00:00-00:00'
+RESOURCE_NAME = l3.ROUTER
+COLLECTION_NAME = l3.ROUTERS
+RESOURCE_ATTRIBUTE_MAP = {
+    COLLECTION_NAME: {
+        FLAVOR_ID: {
+            'allow_post': True, 'allow_put': False,
+            'default': constants.ATTR_NOT_SPECIFIED,
+            'is_visible': True, 'enforce_policy': True
+        }
+    }
+}
+SUB_RESOURCE_ATTRIBUTE_MAP = {}
+ACTION_MAP = {}
+REQUIRED_EXTENSIONS = ['flavors', l3.ALIAS]
+OPTIONAL_EXTENSIONS = []
+ACTION_STATUS = {}
diff --git a/neutron_lib/tests/unit/api/definitions/test_l3_flavors.py b/neutron_lib/tests/unit/api/definitions/test_l3_flavors.py
new file mode 100644
index 000000000..ed3a20ee9
--- /dev/null
+++ b/neutron_lib/tests/unit/api/definitions/test_l3_flavors.py
@@ -0,0 +1,20 @@
+#    Licensed under the Apache License, Version 2.0 (the "License"); you may
+#    not use this file except in compliance with the License. You may obtain
+#    a copy of the License at
+#
+#         http://www.apache.org/licenses/LICENSE-2.0
+#
+#    Unless required by applicable law or agreed to in writing, software
+#    distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+#    WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+#    License for the specific language governing permissions and limitations
+#    under the License.
+
+from neutron_lib.api.definitions import l3_flavors
+from neutron_lib.tests.unit.api.definitions import base
+
+
+class L3FlavorsDefinitionTestCase(base.DefinitionBaseTestCase):
+    extension_module = l3_flavors
+    extension_resources = ()
+    extension_attributes = (l3_flavors.FLAVOR_ID,)
diff --git a/releasenotes/notes/rehome-l3flavors-apidef-da5e9b5d46df5cc7.yaml b/releasenotes/notes/rehome-l3flavors-apidef-da5e9b5d46df5cc7.yaml
new file mode 100644
index 000000000..090bf2a4d
--- /dev/null
+++ b/releasenotes/notes/rehome-l3flavors-apidef-da5e9b5d46df5cc7.yaml
@@ -0,0 +1,4 @@
+---
+features:
+  - The ``l3-flavors`` extension's API definition is now available in
+    ``neutron_lib.api.definitions.l3_flavors``.