diff --git a/label_studio/data_manager/managers.py b/label_studio/data_manager/managers.py
index 70c9b81056a5..9abd636d04bb 100644
--- a/label_studio/data_manager/managers.py
+++ b/label_studio/data_manager/managers.py
@@ -494,6 +494,10 @@ def prepared(self, prepare_params=None):
 
         :param prepare_params: prepare params with project, filters, orderings, etc
         :return: ordered and filtered queryset
+
+        Note: For multi-project queries, filters and ordering will use the first project's
+        configuration (label config, custom fields, etc.). This is backwards compatible
+        with single-project queries.
         """
         from projects.models import Project
 
@@ -502,7 +506,14 @@ def prepared(self, prepare_params=None):
         if prepare_params is None:
             return queryset
 
-        project = Project.objects.get(pk=prepare_params.project)
+        # Get the project for filter/ordering configuration
+        # For multi-project queries, use the first project's configuration
+        if prepare_params.is_multi_project:
+            project = Project.objects.get(pk=prepare_params.projects[0])
+        else:
+            # Backwards compatible: prepare_params.project is an int
+            project = Project.objects.get(pk=prepare_params.project)
+
         request = prepare_params.request
         queryset = apply_filters(queryset, prepare_params.filters, project, request)
         queryset = apply_ordering(queryset, prepare_params.ordering, project, request, view_data=prepare_params.data)
@@ -774,7 +785,11 @@ def get_queryset(
 
     def only_filtered(self, prepare_params=None):
         request = prepare_params.request
-        queryset = TaskQuerySet(self.model).filter(project=prepare_params.project)
+        # Support both single and multiple projects
+        if prepare_params.is_multi_project:
+            queryset = TaskQuerySet(self.model).filter(project__in=prepare_params.projects)
+        else:
+            queryset = TaskQuerySet(self.model).filter(project=prepare_params.project)
         fields_for_filter_ordering = get_fields_for_filter_ordering(prepare_params)
         queryset = self.annotate_queryset(queryset, fields_for_evaluation=fields_for_filter_ordering, request=request)
         return queryset.prepared(prepare_params=prepare_params)
diff --git a/label_studio/data_manager/prepare_params.py b/label_studio/data_manager/prepare_params.py
index 131daa3ac25d..ad087df49638 100644
--- a/label_studio/data_manager/prepare_params.py
+++ b/label_studio/data_manager/prepare_params.py
@@ -37,13 +37,25 @@ class SelectedItems(BaseModel):
 
 
 class PrepareParams(BaseModel):
-    project: int
+    project: Union[int, List[int]]  # Support both single project and multiple projects
     ordering: List[str] = []
     selectedItems: Optional[SelectedItems] = None
     filters: Optional[Filters] = None
     data: Optional[dict] = None
     request: Optional[Any] = None
 
+    @property
+    def projects(self) -> List[int]:
+        """Get project IDs as a list, whether single or multiple were provided."""
+        if isinstance(self.project, list):
+            return self.project
+        return [self.project]
+
+    @property
+    def is_multi_project(self) -> bool:
+        """Check if this PrepareParams includes multiple projects."""
+        return isinstance(self.project, list) and len(self.project) > 1
+
 
 class CustomEnum(Enum):
     def __init__(self, value, description):