diff --git a/codex-rs/core/src/client.rs b/codex-rs/core/src/client.rs
index 74a2f15c1..25de3d33e 100644
--- a/codex-rs/core/src/client.rs
+++ b/codex-rs/core/src/client.rs
@@ -315,7 +315,10 @@ impl ModelClient {
             instructions: &instructions,
         };
 
-        let extra_headers = self.build_subagent_headers();
+        let mut extra_headers = self.build_subagent_headers();
+        extra_headers.extend(build_conversation_headers(Some(
+            self.state.conversation_id.to_string(),
+        )));
         client
             .compact_input(&payload, extra_headers)
             .await
diff --git a/codex-rs/core/tests/suite/compact_remote.rs b/codex-rs/core/tests/suite/compact_remote.rs
index 1d450f9b1..573f38930 100644
--- a/codex-rs/core/tests/suite/compact_remote.rs
+++ b/codex-rs/core/tests/suite/compact_remote.rs
@@ -77,6 +77,7 @@ async fn remote_compact_replaces_history_for_followups() -> Result<()> {
     )
     .await?;
     let codex = harness.test().codex.clone();
+    let session_id = harness.test().session_configured.session_id.to_string();
 
     let responses_mock = responses::mount_sse_sequence(
         harness.server(),
@@ -137,6 +138,10 @@ async fn remote_compact_replaces_history_for_followups() -> Result<()> {
         compact_request.header("authorization").as_deref(),
         Some("Bearer Access Token")
     );
+    assert_eq!(
+        compact_request.header("session_id").as_deref(),
+        Some(session_id.as_str())
+    );
     let compact_body = compact_request.body_json();
     assert_eq!(
         compact_body.get("model").and_then(|v| v.as_str()),
@@ -195,6 +200,7 @@ async fn remote_compact_runs_automatically() -> Result<()> {
     )
     .await?;
     let codex = harness.test().codex.clone();
+    let session_id = harness.test().session_configured.session_id.to_string();
 
     mount_sse_once(
         harness.server(),
@@ -237,6 +243,13 @@ async fn remote_compact_runs_automatically() -> Result<()> {
     wait_for_event(&codex, |event| matches!(event, EventMsg::TurnComplete(_))).await;
     assert!(message);
     assert_eq!(compact_mock.requests().len(), 1);
+    assert_eq!(
+        compact_mock
+            .single_request()
+            .header("session_id")
+            .as_deref(),
+        Some(session_id.as_str())
+    );
     let follow_up_request = responses_mock.single_request();
     let follow_up_body = follow_up_request.body_json().to_string();
     assert!(follow_up_body.contains("REMOTE_COMPACTED_SUMMARY"));