diff --git a/neutron_lib/api/definitions/__init__.py b/neutron_lib/api/definitions/__init__.py
index dfa72429b..634640919 100644
--- a/neutron_lib/api/definitions/__init__.py
+++ b/neutron_lib/api/definitions/__init__.py
@@ -31,6 +31,7 @@ from neutron_lib.api.definitions import firewallrouterinsertion
 from neutron_lib.api.definitions import ip_allocation
 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 logging
 from neutron_lib.api.definitions import logging_resource
 from neutron_lib.api.definitions import network
@@ -76,6 +77,7 @@ _ALL_API_DEFINITIONS = {
     ip_allocation,
     l2_adjacency,
     l3,
+    l3_ext_gw_mode,
     logging,
     logging_resource,
     network,
diff --git a/neutron_lib/api/definitions/l3_ext_gw_mode.py b/neutron_lib/api/definitions/l3_ext_gw_mode.py
new file mode 100644
index 000000000..0a73b5481
--- /dev/null
+++ b/neutron_lib/api/definitions/l3_ext_gw_mode.py
@@ -0,0 +1,59 @@
+# Copyright 2013 VMware, Inc.
+# All rights reserved.
+#
+#    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 import converters
+from neutron_lib.api.definitions import l3
+
+
+ALIAS = 'ext-gw-mode'
+IS_SHIM_EXTENSION = False
+IS_STANDARD_ATTR_EXTENSION = False
+NAME = 'Neutron L3 Configurable external gateway mode'
+API_PREFIX = ''
+DESCRIPTION = ('Extension of the router abstraction for specifying whether '
+               'SNAT should occur on the external gateway')
+UPDATED_TIMESTAMP = '2013-03-28T10:00:00-00:00'
+RESOURCE_NAME = l3.ROUTER
+COLLECTION_NAME = l3.ROUTERS
+RESOURCE_ATTRIBUTE_MAP = {
+    COLLECTION_NAME: {
+        l3.EXTERNAL_GW_INFO: {
+            'allow_post': True,
+            'allow_put': True,
+            'is_visible': True,
+            'default': None,
+            'enforce_policy': True,
+            'validate': {
+                'type:dict_or_nodata': {
+                    'network_id': {'type:uuid': None, 'required': True},
+                    'enable_snat': {'type:boolean': None, 'required': False,
+                                    'convert_to':
+                                        converters.convert_to_boolean},
+                    'external_fixed_ips': {
+                        'convert_list_to': converters.convert_kvp_list_to_dict,
+                        'type:fixed_ips': None,
+                        'default': None,
+                        'required': False
+                    }
+                }
+            }
+        }
+    }
+}
+SUB_RESOURCE_ATTRIBUTE_MAP = {}
+ACTION_MAP = {}
+REQUIRED_EXTENSIONS = [l3.ALIAS]
+OPTIONAL_EXTENSIONS = []
+ACTION_STATUS = {}
diff --git a/neutron_lib/tests/unit/api/definitions/test_l3_ext_gw_mode.py b/neutron_lib/tests/unit/api/definitions/test_l3_ext_gw_mode.py
new file mode 100644
index 000000000..17e85d731
--- /dev/null
+++ b/neutron_lib/tests/unit/api/definitions/test_l3_ext_gw_mode.py
@@ -0,0 +1,19 @@
+#    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_ext_gw_mode
+from neutron_lib.tests.unit.api.definitions import base
+
+
+class L3ExtendedGatewayModeDefinitionTestCase(base.DefinitionBaseTestCase):
+    extension_module = l3_ext_gw_mode
+    extension_attributes = ('external_gateway_info',)
diff --git a/releasenotes/notes/rehome-l3extgwmode-apidef-8f83e0f6cf0515e7.yaml b/releasenotes/notes/rehome-l3extgwmode-apidef-8f83e0f6cf0515e7.yaml
new file mode 100644
index 000000000..262e3b7d5
--- /dev/null
+++ b/releasenotes/notes/rehome-l3extgwmode-apidef-8f83e0f6cf0515e7.yaml
@@ -0,0 +1,4 @@
+---
+features:
+  - The API defintion for the ``ext-gw-mode`` extension is now available in
+    ``neutron_lib.api.definitions.l3_ext_gw_mode``.