diff --git a/hyperactor_multiprocess/src/system_actor.rs b/hyperactor_multiprocess/src/system_actor.rs
index 2712a3950..f668b5a54 100644
--- a/hyperactor_multiprocess/src/system_actor.rs
+++ b/hyperactor_multiprocess/src/system_actor.rs
@@ -1890,6 +1890,14 @@ mod tests {
         }
     }
 
+    // V0-specific test - no V1 equivalent. Unit test for
+    // SystemSupervisionState which tracks proc health and failed
+    // actors centrally at world level. Tests heartbeat timeout
+    // detection (marks procs expired if no heartbeat within timeout)
+    // and failed actor aggregation. V1 does not have centralized
+    // supervision state - V1 uses local supervision where actors
+    // handle ActorSupervisionEvent locally rather than reporting to a
+    // central SystemActor for world-level health monitoring.
     #[tokio::test]
     async fn test_supervision_state() {
         let mut sv = SystemSupervisionState::new(Duration::from_secs(1));
@@ -1989,6 +1997,16 @@ mod tests {
         );
     }
 
+    // V0-specific test - no V1 equivalent. Tests SystemActor world
+    // orchestration where hosts can join before world is created.
+    // Flow: hosts send Join messages → queued by SystemActor →
+    // UpsertWorld defines world topology → SystemActor sends
+    // SpawnProc messages telling each host which procs to spawn.
+    // Verifies correct proc assignment across hosts. V1 does not have
+    // this orchestration model - V1 uses coordinated ProcMesh
+    // allocation where meshes are allocated in one operation, not
+    // assembled from hosts independently joining a central
+    // SystemActor.
     #[tracing_test::traced_test]
     #[tokio::test]
     async fn test_host_join_before_world() {
@@ -2064,6 +2082,14 @@ mod tests {
         }
     }
 
+    // V0-specific test - no V1 equivalent. Tests SystemActor world
+    // orchestration where world is created before hosts join (reverse
+    // order of test_host_join_before_world). Flow: UpsertWorld
+    // defines topology → hosts send Join messages → SystemActor
+    // immediately sends SpawnProc messages. Tests that join order
+    // doesn't matter. V1 does not have this orchestration model - V1
+    // uses coordinated ProcMesh allocation where meshes are allocated
+    // in one operation.
     #[tokio::test]
     async fn test_host_join_after_world() {
         // Spins up a new world with 2 hosts, with 3 procs each.
@@ -2138,6 +2164,12 @@ mod tests {
         }
     }
 
+    // V0-specific test - no V1 equivalent. Unit test for
+    // SystemSnapshotFilter which filters worlds by name and labels
+    // when querying SystemActor. Tests world_matches() and
+    // labels_match() logic. V1 does not have SystemActor or
+    // SystemSnapshot - V1 uses mesh-based iteration and state queries
+    // instead.
     #[test]
     fn test_snapshot_filter() {
         let test_world = World::new(
@@ -2176,6 +2208,13 @@ mod tests {
         ));
     }
 
+    // V0-specific test - no V1 equivalent. Tests SystemActor
+    // supervision behavior when mailbox server crashes: undeliverable
+    // messages are handled AND system supervision detects the
+    // unhealthy world state. V1 does not have SystemActor or world
+    // supervision. V1 undeliverable message handling (without
+    // supervision) is tested in
+    // hyperactor_mesh/src/v1/actor_mesh.rs::test_undeliverable_message_return.
     #[tokio::test]
     async fn test_undeliverable_message_return() {
         // System can't send a message to a remote actor because the
@@ -2349,6 +2388,13 @@ mod tests {
         ));
     }
 
+    // V0-specific test - no V1 equivalent. Tests SystemActor stop
+    // when system is empty (no worlds). Sends SystemMessage::Stop to
+    // central SystemActor which coordinates shutdown of all worlds.
+    // V1 does not have a central SystemActor - V1 uses mesh-level
+    // stop operations (ProcMesh::stop(), HostMesh::shutdown()) where
+    // you stop individual meshes rather than a system-wide
+    // coordinator.
     #[tokio::test]
     async fn test_stop_fast() -> Result<()> {
         let server_handle = System::serve(
@@ -2380,6 +2426,12 @@ mod tests {
         Ok(())
     }
 
+    // V0-specific test - no V1 equivalent. Tests ReportingRouter's
+    // UpdateAddress behavior in simnet mode. When messages are sent,
+    // post_update_address() sends MailboxAdminMessage::UpdateAddress
+    // to update address caches with simnet source routing info. V1
+    // does not have ReportingRouter or dynamic address updates - V1
+    // uses static/direct addressing.
     #[tokio::test]
     async fn test_update_sim_address() {
         simnet::start();