diff --git a/codex-rs/analytics/src/analytics_client_tests.rs b/codex-rs/analytics/src/analytics_client_tests.rs
index 73ea42d760..b44a360364 100644
--- a/codex-rs/analytics/src/analytics_client_tests.rs
+++ b/codex-rs/analytics/src/analytics_client_tests.rs
@@ -454,6 +454,7 @@ fn subagent_thread_started_review_serializes_expected_shape() {
     let event = TrackEventRequest::ThreadInitialized(subagent_thread_started_event_request(
         SubAgentThreadStartedInput {
             thread_id: "thread-review".to_string(),
+            parent_thread_id: None,
             product_client_id: "codex-tui".to_string(),
             client_name: "codex-tui".to_string(),
             client_version: "1.0.0".to_string(),
@@ -496,6 +497,7 @@ fn subagent_thread_started_thread_spawn_serializes_parent_thread_id() {
     let event = TrackEventRequest::ThreadInitialized(subagent_thread_started_event_request(
         SubAgentThreadStartedInput {
             thread_id: "thread-spawn".to_string(),
+            parent_thread_id: None,
             product_client_id: "codex-tui".to_string(),
             client_name: "codex-tui".to_string(),
             client_version: "1.0.0".to_string(),
@@ -526,6 +528,7 @@ fn subagent_thread_started_memory_consolidation_serializes_expected_shape() {
     let event = TrackEventRequest::ThreadInitialized(subagent_thread_started_event_request(
         SubAgentThreadStartedInput {
             thread_id: "thread-memory".to_string(),
+            parent_thread_id: None,
             product_client_id: "codex-tui".to_string(),
             client_name: "codex-tui".to_string(),
             client_version: "1.0.0".to_string(),
@@ -550,6 +553,7 @@ fn subagent_thread_started_other_serializes_expected_shape() {
     let event = TrackEventRequest::ThreadInitialized(subagent_thread_started_event_request(
         SubAgentThreadStartedInput {
             thread_id: "thread-guardian".to_string(),
+            parent_thread_id: None,
             product_client_id: "codex-tui".to_string(),
             client_name: "codex-tui".to_string(),
             client_version: "1.0.0".to_string(),
@@ -562,6 +566,31 @@ fn subagent_thread_started_other_serializes_expected_shape() {
 
     let payload = serde_json::to_value(&event).expect("serialize other subagent event");
     assert_eq!(payload["event_params"]["subagent_source"], "guardian");
+    assert_eq!(payload["event_params"]["parent_thread_id"], json!(null));
+}
+
+#[test]
+fn subagent_thread_started_other_serializes_explicit_parent_thread_id() {
+    let event = TrackEventRequest::ThreadInitialized(subagent_thread_started_event_request(
+        SubAgentThreadStartedInput {
+            thread_id: "thread-guardian".to_string(),
+            parent_thread_id: Some("parent-thread-guardian".to_string()),
+            product_client_id: "codex-tui".to_string(),
+            client_name: "codex-tui".to_string(),
+            client_version: "1.0.0".to_string(),
+            model: "gpt-5".to_string(),
+            ephemeral: false,
+            subagent_source: SubAgentSource::Other("guardian".to_string()),
+            created_at: 126,
+        },
+    ));
+
+    let payload = serde_json::to_value(&event).expect("serialize guardian subagent event");
+    assert_eq!(payload["event_params"]["subagent_source"], "guardian");
+    assert_eq!(
+        payload["event_params"]["parent_thread_id"],
+        "parent-thread-guardian"
+    );
 }
 
 #[tokio::test]
@@ -574,6 +603,7 @@ async fn subagent_thread_started_publishes_without_initialize() {
             AnalyticsFact::Custom(CustomAnalyticsFact::SubAgentThreadStarted(
                 SubAgentThreadStartedInput {
                     thread_id: "thread-review".to_string(),
+                    parent_thread_id: None,
                     product_client_id: "codex-tui".to_string(),
                     client_name: "codex-tui".to_string(),
                     client_version: "1.0.0".to_string(),
diff --git a/codex-rs/analytics/src/events.rs b/codex-rs/analytics/src/events.rs
index 885e93bbb9..d2e59f8608 100644
--- a/codex-rs/analytics/src/events.rs
+++ b/codex-rs/analytics/src/events.rs
@@ -249,7 +249,9 @@ pub(crate) fn subagent_thread_started_event_request(
         thread_source: Some("subagent"),
         initialization_mode: ThreadInitializationMode::New,
         subagent_source: Some(subagent_source_name(&input.subagent_source)),
-        parent_thread_id: subagent_parent_thread_id(&input.subagent_source),
+        parent_thread_id: input
+            .parent_thread_id
+            .or_else(|| subagent_parent_thread_id(&input.subagent_source)),
         created_at: input.created_at,
     };
     ThreadInitializedEvent {
diff --git a/codex-rs/analytics/src/facts.rs b/codex-rs/analytics/src/facts.rs
index e19d15d847..e55309fe31 100644
--- a/codex-rs/analytics/src/facts.rs
+++ b/codex-rs/analytics/src/facts.rs
@@ -54,6 +54,7 @@ pub struct AppInvocation {
 #[derive(Clone)]
 pub struct SubAgentThreadStartedInput {
     pub thread_id: String,
+    pub parent_thread_id: Option<String>,
     pub product_client_id: String,
     pub client_name: String,
     pub client_version: String,
diff --git a/codex-rs/core/src/agent/control.rs b/codex-rs/core/src/agent/control.rs
index 529615a7a5..d60d1a9fff 100644
--- a/codex-rs/core/src/agent/control.rs
+++ b/codex-rs/core/src/agent/control.rs
@@ -283,6 +283,7 @@ impl AgentControl {
                     .analytics_events_client,
                 client_metadata,
                 new_thread.thread_id,
+                /*parent_thread_id*/ None,
                 thread_config,
                 subagent_source.clone(),
             );
diff --git a/codex-rs/core/src/codex.rs b/codex-rs/core/src/codex.rs
index 1d38280fa9..2dea5e3a3e 100644
--- a/codex-rs/core/src/codex.rs
+++ b/codex-rs/core/src/codex.rs
@@ -4582,6 +4582,7 @@ pub(crate) fn emit_subagent_session_started(
     analytics_events_client: &AnalyticsEventsClient,
     client_metadata: AppServerClientMetadata,
     thread_id: ThreadId,
+    parent_thread_id: Option<ThreadId>,
     thread_config: ThreadConfigSnapshot,
     subagent_source: SubAgentSource,
 ) {
@@ -4599,6 +4600,7 @@ pub(crate) fn emit_subagent_session_started(
         .as_secs();
     analytics_events_client.track_subagent_thread_started(SubAgentThreadStartedInput {
         thread_id: thread_id.to_string(),
+        parent_thread_id: parent_thread_id.map(|thread_id| thread_id.to_string()),
         product_client_id: client_name.clone(),
         client_name,
         client_version,
diff --git a/codex-rs/core/src/codex_delegate.rs b/codex-rs/core/src/codex_delegate.rs
index 3d74773ba7..1e07c6d1ff 100644
--- a/codex-rs/core/src/codex_delegate.rs
+++ b/codex-rs/core/src/codex_delegate.rs
@@ -104,6 +104,7 @@ pub(crate) async fn run_codex_thread_interactive(
             &parent_session.services.analytics_events_client,
             client_metadata,
             codex.session.conversation_id,
+            Some(parent_session.conversation_id),
             thread_config,
             subagent_source,
         );
diff --git a/codex-rs/core/src/memories/phase2.rs b/codex-rs/core/src/memories/phase2.rs
index fde135d5e2..203a19075c 100644
--- a/codex-rs/core/src/memories/phase2.rs
+++ b/codex-rs/core/src/memories/phase2.rs
@@ -156,6 +156,7 @@ pub(super) async fn run(session: &Arc<Session>, config: Arc<Config>) {
                 &session.services.analytics_events_client,
                 client_metadata,
                 thread_id,
+                /*parent_thread_id*/ None,
                 thread_config,
                 SubAgentSource::MemoryConsolidation,
             );