diff --git a/codex-rs/core/src/client.rs b/codex-rs/core/src/client.rs
index 48623a00e8..a8ef00bcc1 100644
--- a/codex-rs/core/src/client.rs
+++ b/codex-rs/core/src/client.rs
@@ -1912,6 +1912,7 @@ where
         let mut logged_error = false;
         let mut tx_last_response = Some(tx_last_response);
         let mut items_added: Vec<ResponseItem> = Vec::new();
+        let (request_start, mut ttft_ms) = (Instant::now(), None);
         let mut api_stream = api_stream;
         let upstream_request_id = upstream_request_id.as_deref();
         if let Some(upstream_request_id) = upstream_request_id {
@@ -1961,6 +1962,7 @@ where
                             Some(usage.cached_input_tokens),
                             Some(usage.reasoning_output_tokens),
                             usage.total_tokens,
+                            ttft_ms,
                         );
                     }
                     inference_trace_attempt.record_completed(
@@ -1988,6 +1990,11 @@ where
                     }
                 }
                 Ok(event) => {
+                    if matches!(&event, ResponseEvent::OutputItemAdded(_)) && ttft_ms.is_none() {
+                        ttft_ms = Some(
+                            i64::try_from(request_start.elapsed().as_millis()).unwrap_or(i64::MAX),
+                        );
+                    }
                     if tx_event.send(Ok(event)).await.is_err() {
                         inference_trace_attempt.record_cancelled(
                             STREAM_DROPPED_REASON,
diff --git a/codex-rs/core/tests/suite/otel.rs b/codex-rs/core/tests/suite/otel.rs
index e3415d945b..4a2b2993ad 100644
--- a/codex-rs/core/tests/suite/otel.rs
+++ b/codex-rs/core/tests/suite/otel.rs
@@ -567,19 +567,22 @@ async fn process_sse_emits_completed_telemetry() {
 
     mount_sse_once(
         &server,
-        sse(vec![serde_json::json!({
-            "type": "response.completed",
-            "response": {
-                "id": "resp1",
-                "usage": {
-                    "input_tokens": 3,
-                    "input_tokens_details": { "cached_tokens": 1 },
-                    "output_tokens": 5,
-                    "output_tokens_details": { "reasoning_tokens": 2 },
-                    "total_tokens": 9
+        sse(vec![
+            ev_reasoning_item_added("reasoning-1", &[]),
+            serde_json::json!({
+                "type": "response.completed",
+                "response": {
+                    "id": "resp1",
+                    "usage": {
+                        "input_tokens": 3,
+                        "input_tokens_details": { "cached_tokens": 1 },
+                        "output_tokens": 5,
+                        "output_tokens_details": { "reasoning_tokens": 2 },
+                        "total_tokens": 9
+                    }
                 }
-            }
-        })]),
+            }),
+        ]),
     )
     .await;
 
@@ -612,6 +615,9 @@ async fn process_sse_emits_completed_telemetry() {
                     && line.contains("cached_token_count=1")
                     && line.contains("reasoning_token_count=2")
                     && line.contains("tool_token_count=9")
+                    && extract_log_field(line, "ttft_ms")
+                        .and_then(|ttft_ms| ttft_ms.parse::<i64>().ok())
+                        .is_some()
             })
             .map(|_| Ok(()))
             .unwrap_or(Err("missing response.completed telemetry".to_string()))
diff --git a/codex-rs/otel/src/events/session_telemetry.rs b/codex-rs/otel/src/events/session_telemetry.rs
index 8210c0e5b9..440f8f04a5 100644
--- a/codex-rs/otel/src/events/session_telemetry.rs
+++ b/codex-rs/otel/src/events/session_telemetry.rs
@@ -910,6 +910,7 @@ impl SessionTelemetry {
         cached_token_count: Option<i64>,
         reasoning_token_count: Option<i64>,
         tool_token_count: i64,
+        ttft_ms: Option<i64>,
     ) {
         log_and_trace_event!(
             self,
@@ -921,6 +922,7 @@ impl SessionTelemetry {
                 cached_token_count = cached_token_count,
                 reasoning_token_count = reasoning_token_count,
                 tool_token_count = %tool_token_count,
+                ttft_ms = ttft_ms,
                 service_tier = self.metadata.service_tier.as_deref(),
                 model_reasoning_effort = self.metadata.model_reasoning_effort.as_deref(),
             },