diff --git a/spec/changelog.yml b/spec/changelog.yml
index 16797f49..696ec167 100644
--- a/spec/changelog.yml
+++ b/spec/changelog.yml
@@ -2,6 +2,11 @@
 ## This file documents changes in the package specification. It is NOT a package specification file.
 ## Newer entries go at the bottom of each in-development version.
 ##
+- version: 2.0.0-next
+  changes:
+  - description: Add setting to configure the source mode of a data stream
+    type: enhancement
+    link: https://github.com/elastic/package-spec/issues/340
 - version: 2.0.0-rc2
   changes:
   - description: Add map as another reference type to check to show warnings
diff --git a/spec/integration/data_stream/manifest.spec.yml b/spec/integration/data_stream/manifest.spec.yml
index b54411cc..5cb27c5f 100644
--- a/spec/integration/data_stream/manifest.spec.yml
+++ b/spec/integration/data_stream/manifest.spec.yml
@@ -222,5 +222,19 @@ spec:
               type: array
               items:
                 type: string
+        source_mode:
+          description: |-
+            Source mode to use. This configures how the document source (`_source`) is stored
+            for this data stream.
+            If configured as `default`, this mode is not configured and it uses Elasticsearch defaults.
+            If configured as `synthetic`, it enables [synthetic source](https://www.elastic.co/guide/en/elasticsearch/reference/8.4/mapping-source-field.html#synthetic-source),
+            that doesn't store the source, but tries to rebuild it from the indexed fields when queried.
+            If no configured or set to `synthetic`, users may override the setting from Fleet UI.
+          type: string
+          enum:
+          - "default"
+          - "synthetic"
+          examples:
+          - "synthetic"
   required:
   - title
diff --git a/test/packages/good/data_stream/k8s_data_stream/manifest.yml b/test/packages/good/data_stream/k8s_data_stream/manifest.yml
index 9348ebc2..bedfa836 100644
--- a/test/packages/good/data_stream/k8s_data_stream/manifest.yml
+++ b/test/packages/good/data_stream/k8s_data_stream/manifest.yml
@@ -12,3 +12,5 @@ streams:
         default: /server-status
     title: Nginx access logs
     description: Collect Nginx access logs
+elasticsearch:
+  source_mode: "default"
diff --git a/test/packages/time_series/data_stream/example/manifest.yml b/test/packages/time_series/data_stream/example/manifest.yml
index 3a3147c6..a4d2bbeb 100644
--- a/test/packages/time_series/data_stream/example/manifest.yml
+++ b/test/packages/time_series/data_stream/example/manifest.yml
@@ -11,6 +11,7 @@ streams:
         default: 10s
 
 elasticsearch:
+  source_mode: "synthetic"
   index_mode: "time_series"
   index_template:
     settings: