diff --git a/hyperactor_mesh/src/v1/actor_mesh.rs b/hyperactor_mesh/src/v1/actor_mesh.rs
index 1fb9e76ff..05f29aa22 100644
--- a/hyperactor_mesh/src/v1/actor_mesh.rs
+++ b/hyperactor_mesh/src/v1/actor_mesh.rs
@@ -469,6 +469,7 @@ mod tests {
     use crate::v1::ActorMeshRef;
     use crate::v1::Name;
     use crate::v1::ProcMesh;
+    use crate::v1::proc_mesh::ACTOR_SPAWN_MAX_IDLE;
     use crate::v1::proc_mesh::GET_ACTOR_STATE_MAX_IDLE;
     use crate::v1::testactor;
     use crate::v1::testing;
@@ -938,4 +939,97 @@ mod tests {
             n, count
         );
     }
+
+    /// Test that actors not responding within stop timeout are
+    /// forcibly aborted. This is the V1 equivalent of
+    /// hyperactor_multiprocess/src/proc_actor.rs::test_stop_timeout.
+    #[async_timed_test(timeout_secs = 30)]
+    #[cfg(fbcode_build)]
+    async fn test_actor_mesh_stop_timeout() {
+        hyperactor_telemetry::initialize_logging_for_test();
+
+        // Override ACTOR_SPAWN_MAX_IDLE to make test fast and
+        // deterministic. ACTOR_SPAWN_MAX_IDLE is the maximum idle
+        // time between status updates during mesh operations
+        // (spawn/stop). When stop() is called, it waits for actors to
+        // report they've stopped. If actors don't respond within this
+        // timeout, they're forcibly aborted via JoinHandle::abort().
+        // We set this to 1 second (instead of default 30s) so hung
+        // actors (sleeping 5s in this test) get aborted quickly,
+        // making the test fast.
+        let config = hyperactor::config::global::lock();
+        let _guard = config.override_key(ACTOR_SPAWN_MAX_IDLE, std::time::Duration::from_secs(1));
+
+        let instance = testing::instance().await;
+
+        // Create proc mesh with 2 replicas
+        let meshes = testing::proc_meshes(instance, extent!(replicas = 2)).await;
+        let proc_mesh = &meshes[1]; // Use ProcessAllocator version
+
+        // Spawn SleepActors across the mesh that will block longer
+        // than timeout
+        let sleep_mesh = proc_mesh
+            .spawn::<testactor::SleepActor>(instance, "sleepers", &())
+            .await
+            .unwrap();
+
+        // Send each actor a message to sleep for 5 seconds (longer
+        // than 1-second timeout)
+        for actor_ref in sleep_mesh.values() {
+            actor_ref
+                .send(instance, std::time::Duration::from_secs(5))
+                .unwrap();
+        }
+
+        // Give actors time to start sleeping
+        RealClock.sleep(std::time::Duration::from_millis(200)).await;
+
+        // Count how many actors we spawned (for verification later)
+        let expected_actors = sleep_mesh.values().count();
+
+        // Now stop the mesh - actors won't respond in time, should be
+        // aborted. Time this operation to verify abort behavior.
+        let stop_start = RealClock.now();
+        let result = sleep_mesh.stop(instance).await;
+        let stop_duration = RealClock.now().duration_since(stop_start);
+
+        // Stop will return an error because actors didn't stop within
+        // the timeout. This is expected - the actors were forcibly
+        // aborted, and V1 reports this as an error.
+        match result {
+            Ok(_) => {
+                // It's possible actors stopped in time, but unlikely
+                // given 5-second sleep vs 1-second timeout
+                tracing::warn!("Actors stopped gracefully (unexpected but ok)");
+            }
+            Err(ref e) => {
+                // Expected: timeout error indicating actors were aborted
+                let err_str = format!("{:?}", e);
+                assert!(
+                    err_str.contains("Timeout"),
+                    "Expected Timeout error, got: {:?}",
+                    e
+                );
+                tracing::info!(
+                    "Stop timed out as expected for {} actors, they were aborted",
+                    expected_actors
+                );
+            }
+        }
+
+        // Verify that stop completed quickly (~1-2 seconds for
+        // timeout + abort) rather than waiting the full 5 seconds for
+        // actors to finish sleeping. This proves actors were aborted,
+        // not waited for.
+        assert!(
+            stop_duration < std::time::Duration::from_secs(3),
+            "Stop took {:?}, expected < 3s (actors should have been aborted, not waited for)",
+            stop_duration
+        );
+        assert!(
+            stop_duration >= std::time::Duration::from_millis(900),
+            "Stop took {:?}, expected >= 900ms (should have waited for timeout)",
+            stop_duration
+        );
+    }
 }
diff --git a/hyperactor_mesh/src/v1/testactor.rs b/hyperactor_mesh/src/v1/testactor.rs
index df56443d4..49a15939d 100644
--- a/hyperactor_mesh/src/v1/testactor.rs
+++ b/hyperactor_mesh/src/v1/testactor.rs
@@ -29,9 +29,7 @@ use hyperactor::Named;
 use hyperactor::PortRef;
 use hyperactor::RefClient;
 use hyperactor::Unbind;
-#[cfg(test)]
 use hyperactor::clock::Clock as _;
-#[cfg(test)]
 use hyperactor::clock::RealClock;
 use hyperactor::config;
 use hyperactor::config::global::Source;
@@ -159,6 +157,27 @@ impl Handler<ActorSupervisionEvent> for TestActorWithSupervisionHandling {
     }
 }
 
+/// A test actor that sleeps when it receives a Duration message.
+/// Used for testing timeout and abort behavior.
+#[derive(Actor, Default, Debug)]
+#[hyperactor::export(
+    spawn = true,
+    handlers = [std::time::Duration],
+)]
+pub struct SleepActor;
+
+#[async_trait]
+impl Handler<std::time::Duration> for SleepActor {
+    async fn handle(
+        &mut self,
+        _cx: &Context<Self>,
+        duration: std::time::Duration,
+    ) -> Result<(), anyhow::Error> {
+        RealClock.sleep(duration).await;
+        Ok(())
+    }
+}
+
 /// A message to forward to a visit list of ports.
 /// Each port removes the next entry, and adds it to the
 /// 'visited' list.
diff --git a/hyperactor_multiprocess/src/proc_actor.rs b/hyperactor_multiprocess/src/proc_actor.rs
index 62725cacd..9ee0784f3 100644
--- a/hyperactor_multiprocess/src/proc_actor.rs
+++ b/hyperactor_multiprocess/src/proc_actor.rs
@@ -1063,16 +1063,14 @@ mod tests {
         }
     }
 
-    // V0 test - V1 needs equivalent coverage. Tests that actors not
+    // V0 test - V1 has equivalent coverage. Tests that actors not
     // responding within stop timeout are forcibly aborted
     // (JoinHandle::abort). Spawns SleepActors that block for 5
     // seconds, calls stop() with 1-second timeout, verifies abort
-    // counts and "aborting JoinHandle" logs. V1 uses the same
-    // underlying mechanism (Proc::destroy_and_wait) but lacks test
-    // coverage. V1's ActorMesh::stop() uses global config timeout
-    // (ACTOR_SPAWN_MAX_IDLE) and doesn't expose stopped/aborted
-    // counts, but equivalent tests should verify timeout and abort
-    // behavior work correctly.
+    // counts and "aborting JoinHandle" logs. V1 equivalent:
+    // hyperactor_mesh/src/v1/actor_mesh.rs::test_actor_mesh_stop_timeout.
+    // Both use the same underlying mechanism (Proc::destroy_and_wait),
+    // but V1 returns Err(Timeout) instead of Ok with abort counts.
     #[tracing_test::traced_test]
     #[tokio::test]
     #[cfg_attr(not(fbcode_build), ignore)]
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();