diff --git a/api-ref/source/v3/ext-backups.inc b/api-ref/source/v3/ext-backups.inc
index a96dee52465..0fe80953a37 100644
--- a/api-ref/source/v3/ext-backups.inc
+++ b/api-ref/source/v3/ext-backups.inc
@@ -87,6 +87,7 @@ Response Parameters
    - is_incremental: is_incremental
    - data_timestamp: data_timestamp
    - snapshot_id: snapshot_id_2
+   - os-backup-project-attr:project_id: os-backup-project-attr:project_id
 
 Response Example
 ----------------
@@ -139,6 +140,7 @@ Response Parameters
    - is_incremental: is_incremental
    - data_timestamp: data_timestamp
    - snapshot_id: snapshot_id_2
+   - os-backup-project-attr:project_id: os-backup-project-attr:project_id
 
 Response Example
 ----------------
diff --git a/api-ref/source/v3/parameters.yaml b/api-ref/source/v3/parameters.yaml
index 5e48821a294..1441157c3a6 100644
--- a/api-ref/source/v3/parameters.yaml
+++ b/api-ref/source/v3/parameters.yaml
@@ -1383,6 +1383,16 @@ os-attach:
   in: body
   required: true
   type: object
+os-backup-project-attr:project_id:
+  description: |
+    The UUID of the owning project.
+  in: body
+  required: true
+  type: string.
+  in: body
+  required: true
+  type: string
+  min_version: 3.18
 os-detach:
   description: |
     The ``os-detach`` action.
diff --git a/api-ref/source/v3/samples/backup-show-response.json b/api-ref/source/v3/samples/backup-show-response.json
index c4fe0ffc4e5..2b7a2dd86fa 100644
--- a/api-ref/source/v3/samples/backup-show-response.json
+++ b/api-ref/source/v3/samples/backup-show-response.json
@@ -18,8 +18,10 @@
         ],
         "name": "backup001",
         "object_count": 22,
+        "os-backup-project-attr:project_id": "2c67a14be9314c5dae2ee6c4ec90cf0b",
         "size": 1,
         "status": "available",
+        "updated_at": "2013-04-02T10:35:27.000000",
         "volume_id": "e5185058-943a-4cb4-96d9-72c184c337d6",
         "is_incremental": true,
         "has_dependent_backups": false
diff --git a/api-ref/source/v3/samples/backups-list-detailed-response.json b/api-ref/source/v3/samples/backups-list-detailed-response.json
index d729ada6848..d4cb687bf08 100644
--- a/api-ref/source/v3/samples/backups-list-detailed-response.json
+++ b/api-ref/source/v3/samples/backups-list-detailed-response.json
@@ -19,8 +19,10 @@
             ],
             "name": "backup001",
             "object_count": 22,
+            "os-backup-project-attr:project_id": "2c67a14be9314c5dae2ee6c4ec90cf0b",
             "size": 1,
             "status": "available",
+            "updated_at": "2013-04-02T10:35:27.000000",
             "volume_id": "e5185058-943a-4cb4-96d9-72c184c337d6",
             "is_incremental": true,
             "has_dependent_backups": false
@@ -44,8 +46,10 @@
             ],
             "name": "backup002",
             "object_count": 22,
+            "os-backup-project-attr:project_id": "2c67a14be9314c5dae2ee6c4ec90cf0b",
             "size": 1,
             "status": "available",
+            "updated_at": "2013-04-02T10:21:48.000000",
             "volume_id": "e5185058-943a-4cb4-96d9-72c184c337d6",
             "is_incremental": true,
             "has_dependent_backups": false