diff --git a/idc-assets/app-config-template.js b/idc-assets/app-config-template.js
index ba6b8f6f016..3e2b9ef572e 100644
--- a/idc-assets/app-config-template.js
+++ b/idc-assets/app-config-template.js
@@ -79,11 +79,10 @@ window.config = {
     prefetch: 25,
   },
   /**
-   * Default data source - uses merge to combine IDC + GCP.
-   * When no ?gcp= param, only IDC data is shown.
-   * When ?gcp= param is present, both sources are merged.
+   * Default data source - uses IDC DICOMWeb directly.
+   * When ?gcp= param is present, the GCP extension activates the merge data source.
    */
-  defaultDataSourceName: 'idc-merge',
+  defaultDataSourceName: 'idc-dicomweb',
   dataSources: [
     /**
      * IDC's primary DICOMWeb server (static WADO).
diff --git a/platform/app/public/config/default.js b/platform/app/public/config/default.js
index e47db26a510..4cc9a4d8c96 100644
--- a/platform/app/public/config/default.js
+++ b/platform/app/public/config/default.js
@@ -117,11 +117,10 @@ window.config = {
   showErrorDetails: 'always',
 
   /**
-   * Default data source - uses merge to combine IDC + GCP.
-   * When no ?gcp= param, only IDC data is shown.
-   * When ?gcp= param is present, both sources are merged.
+   * Default data source - uses IDC DICOMWeb directly.
+   * When ?gcp= param is present, the GCP extension activates the merge data source.
    */
-  defaultDataSourceName: 'idc-merge',
+  defaultDataSourceName: 'idc-dicomweb',
 
   dataSources: [
     /**
diff --git a/platform/app/public/config/idc.js b/platform/app/public/config/idc.js
index 0bceea7c083..3d6758d2eb5 100644
--- a/platform/app/public/config/idc.js
+++ b/platform/app/public/config/idc.js
@@ -117,11 +117,10 @@ window.config = {
   showErrorDetails: 'always',
 
   /**
-   * Default data source - uses merge to combine IDC + GCP.
-   * When no ?gcp= param, only IDC data is shown.
-   * When ?gcp= param is present, both sources are merged.
+   * Default data source - uses IDC DICOMWeb directly.
+   * When ?gcp= param is present, the GCP extension activates the merge data source.
    */
-  defaultDataSourceName: 'idc-merge',
+  defaultDataSourceName: 'idc-dicomweb',
 
   dataSources: [
     /**