diff --git a/codex-rs/analytics/src/analytics_client_tests.rs b/codex-rs/analytics/src/analytics_client_tests.rs
index 44fc65c792..895c0962cd 100644
--- a/codex-rs/analytics/src/analytics_client_tests.rs
+++ b/codex-rs/analytics/src/analytics_client_tests.rs
@@ -32,6 +32,7 @@ use crate::events::ReviewTrigger;
 use crate::events::Reviewer;
 use crate::events::ThreadInitializedEvent;
 use crate::events::ThreadInitializedEventParams;
+use crate::events::ThreadStartTimingEventParams;
 use crate::events::ToolItemTerminalStatus;
 use crate::events::TrackEventRequest;
 use crate::events::codex_app_metadata;
@@ -1329,10 +1330,12 @@ fn thread_initialized_event_serializes_expected_shape() {
             initialization_mode: ThreadInitializationMode::New,
             subagent_source: None,
             parent_thread_id: None,
-            thread_start_duration_ms: Some(321),
-            thread_start_prepare_duration_ms: Some(111),
-            thread_start_spawn_duration_ms: Some(123),
-            thread_start_finalize_duration_ms: Some(87),
+            thread_start_timing: ThreadStartTimingEventParams {
+                thread_start_duration_ms: Some(321),
+                thread_start_prepare_duration_ms: Some(111),
+                thread_start_spawn_duration_ms: Some(123),
+                thread_start_finalize_duration_ms: Some(87),
+            },
             created_at: 1,
         },
     });
diff --git a/codex-rs/analytics/src/events.rs b/codex-rs/analytics/src/events.rs
index 873b2bdc4d..870de097c6 100644
--- a/codex-rs/analytics/src/events.rs
+++ b/codex-rs/analytics/src/events.rs
@@ -159,6 +159,14 @@ pub(crate) struct CodexAppServerStartedEventRequest {
     pub(crate) event_params: CodexAppServerStartedEventParams,
 }
 
+#[derive(Default, Serialize)]
+pub(crate) struct ThreadStartTimingEventParams {
+    pub(crate) thread_start_duration_ms: Option<u64>,
+    pub(crate) thread_start_prepare_duration_ms: Option<u64>,
+    pub(crate) thread_start_spawn_duration_ms: Option<u64>,
+    pub(crate) thread_start_finalize_duration_ms: Option<u64>,
+}
+
 #[derive(Serialize)]
 pub(crate) struct ThreadInitializedEventParams {
     pub(crate) thread_id: String,
@@ -170,10 +178,8 @@ pub(crate) struct ThreadInitializedEventParams {
     pub(crate) initialization_mode: ThreadInitializationMode,
     pub(crate) subagent_source: Option<String>,
     pub(crate) parent_thread_id: Option<String>,
-    pub(crate) thread_start_duration_ms: Option<u64>,
-    pub(crate) thread_start_prepare_duration_ms: Option<u64>,
-    pub(crate) thread_start_spawn_duration_ms: Option<u64>,
-    pub(crate) thread_start_finalize_duration_ms: Option<u64>,
+    #[serde(flatten)]
+    pub(crate) thread_start_timing: ThreadStartTimingEventParams,
     pub(crate) created_at: u64,
 }
 
@@ -1061,10 +1067,7 @@ pub(crate) fn subagent_thread_started_event_request(
         parent_thread_id: input
             .parent_thread_id
             .or_else(|| subagent_parent_thread_id(&input.subagent_source)),
-        thread_start_duration_ms: None,
-        thread_start_prepare_duration_ms: None,
-        thread_start_spawn_duration_ms: None,
-        thread_start_finalize_duration_ms: None,
+        thread_start_timing: ThreadStartTimingEventParams::default(),
         created_at: input.created_at,
     };
     ThreadInitializedEvent {
diff --git a/codex-rs/analytics/src/reducer.rs b/codex-rs/analytics/src/reducer.rs
index 5075e5baec..1476dc5f3e 100644
--- a/codex-rs/analytics/src/reducer.rs
+++ b/codex-rs/analytics/src/reducer.rs
@@ -47,6 +47,7 @@ use crate::events::SkillInvocationEventParams;
 use crate::events::SkillInvocationEventRequest;
 use crate::events::ThreadInitializedEvent;
 use crate::events::ThreadInitializedEventParams;
+use crate::events::ThreadStartTimingEventParams;
 use crate::events::ToolItemFailureKind;
 use crate::events::ToolItemTerminalStatus;
 use crate::events::TrackEventRequest;
@@ -1309,13 +1310,15 @@ impl AnalyticsReducer {
                     initialization_mode,
                     subagent_source: thread_metadata.subagent_source.clone(),
                     parent_thread_id: thread_metadata.parent_thread_id,
-                    thread_start_duration_ms: thread_start_timing.map(|timing| timing.duration_ms),
-                    thread_start_prepare_duration_ms: thread_start_timing
-                        .map(|timing| timing.prepare_duration_ms),
-                    thread_start_spawn_duration_ms: thread_start_timing
-                        .map(|timing| timing.spawn_duration_ms),
-                    thread_start_finalize_duration_ms: thread_start_timing
-                        .map(|timing| timing.finalize_duration_ms),
+                    thread_start_timing: match thread_start_timing {
+                        Some(timing) => ThreadStartTimingEventParams {
+                            thread_start_duration_ms: Some(timing.duration_ms),
+                            thread_start_prepare_duration_ms: Some(timing.prepare_duration_ms),
+                            thread_start_spawn_duration_ms: Some(timing.spawn_duration_ms),
+                            thread_start_finalize_duration_ms: Some(timing.finalize_duration_ms),
+                        },
+                        None => ThreadStartTimingEventParams::default(),
+                    },
                     created_at: u64::try_from(thread.created_at).unwrap_or_default(),
                 },
             },