diff --git a/letta/server/rest_api/routers/v1/sources.py b/letta/server/rest_api/routers/v1/sources.py
index 082fe6e1..fb41bf80 100644
--- a/letta/server/rest_api/routers/v1/sources.py
+++ b/letta/server/rest_api/routers/v1/sources.py
@@ -324,6 +324,19 @@ async def upload_file_to_source(
     return file_metadata
 
 
+@router.get("/{source_id}/agents", response_model=List[str], operation_id="get_agents_for_source")
+async def get_agents_for_source(
+    source_id: str,
+    server: SyncServer = Depends(get_letta_server),
+    actor_id: Optional[str] = Header(None, alias="user_id"),
+):
+    """
+    Get all agent IDs that have the specified source attached.
+    """
+    actor = await server.user_manager.get_actor_or_default_async(actor_id=actor_id)
+    return await server.source_manager.get_agents_for_source_id(source_id=source_id, actor=actor)
+
+
 @router.get("/{source_id}/passages", response_model=List[Passage], operation_id="list_source_passages")
 async def list_source_passages(
     source_id: str,
diff --git a/letta/services/source_manager.py b/letta/services/source_manager.py
index b3cd2c04..02357c06 100644
--- a/letta/services/source_manager.py
+++ b/letta/services/source_manager.py
@@ -1,7 +1,7 @@
 import asyncio
 from typing import List, Optional
 
-from sqlalchemy import select
+from sqlalchemy import and_, exists, select
 
 from letta.orm import Agent as AgentModel
 from letta.orm.errors import NoResultFound
@@ -19,6 +19,30 @@ from letta.utils import enforce_types, printd
 class SourceManager:
     """Manager class to handle business logic related to Sources."""
 
+    @trace_method
+    async def _validate_source_exists_async(self, session, source_id: str, actor: PydanticUser) -> None:
+        """
+        Validate that a source exists and user has access to it using raw SQL for efficiency.
+
+        Args:
+            session: Database session
+            source_id: ID of the source to validate
+            actor: User performing the action
+
+        Raises:
+            NoResultFound: If source doesn't exist or user doesn't have access
+        """
+        source_exists_query = select(
+            exists().where(
+                and_(SourceModel.id == source_id, SourceModel.organization_id == actor.organization_id, SourceModel.is_deleted == False)
+            )
+        )
+
+        result = await session.execute(source_exists_query)
+
+        if not result.scalar():
+            raise NoResultFound(f"Source with ID {source_id} not found")
+
     @enforce_types
     @trace_method
     async def create_source(self, source: PydanticSource, actor: PydanticUser) -> PydanticSource:
@@ -93,20 +117,20 @@ class SourceManager:
 
     @enforce_types
     @trace_method
-    async def list_attached_agents(self, source_id: str, actor: Optional[PydanticUser] = None) -> List[PydanticAgentState]:
+    async def list_attached_agents(self, source_id: str, actor: PydanticUser) -> List[PydanticAgentState]:
         """
         Lists all agents that have the specified source attached.
 
         Args:
             source_id: ID of the source to find attached agents for
-            actor: User performing the action (optional for now, following existing pattern)
+            actor: User performing the action
 
         Returns:
             List[PydanticAgentState]: List of agents that have this source attached
         """
         async with db_registry.async_session() as session:
             # Verify source exists and user has permission to access it
-            source = await SourceModel.read_async(db_session=session, identifier=source_id, actor=actor)
+            await self._validate_source_exists_async(session, source_id, actor)
 
             # Use junction table query instead of relationship to avoid performance issues
             query = (
@@ -114,7 +138,7 @@ class SourceManager:
                 .join(SourcesAgents, AgentModel.id == SourcesAgents.agent_id)
                 .where(
                     SourcesAgents.source_id == source_id,
-                    AgentModel.organization_id == actor.organization_id if actor else True,
+                    AgentModel.organization_id == actor.organization_id,
                     AgentModel.is_deleted == False,
                 )
                 .order_by(AgentModel.created_at.desc(), AgentModel.id)
@@ -125,6 +149,31 @@ class SourceManager:
 
             return await asyncio.gather(*[agent.to_pydantic_async() for agent in agents_orm])
 
+    @enforce_types
+    @trace_method
+    async def get_agents_for_source_id(self, source_id: str, actor: PydanticUser) -> List[str]:
+        """
+        Get all agent IDs associated with a given source ID.
+
+        Args:
+            source_id: ID of the source to find agents for
+            actor: User performing the action
+
+        Returns:
+            List[str]: List of agent IDs that have this source attached
+        """
+        async with db_registry.async_session() as session:
+            # Verify source exists and user has permission to access it
+            await self._validate_source_exists_async(session, source_id, actor)
+
+            # Query the junction table directly for performance
+            query = select(SourcesAgents.agent_id).where(SourcesAgents.source_id == source_id)
+
+            result = await session.execute(query)
+            agent_ids = result.scalars().all()
+
+            return list(agent_ids)
+
     # TODO: We make actor optional for now, but should most likely be enforced due to security reasons
     @enforce_types
     @trace_method