diff --git a/codex-rs/codex-api/src/endpoint/responses_websocket.rs b/codex-rs/codex-api/src/endpoint/responses_websocket.rs
index 559a8faf0..202a57416 100644
--- a/codex-rs/codex-api/src/endpoint/responses_websocket.rs
+++ b/codex-rs/codex-api/src/endpoint/responses_websocket.rs
@@ -225,9 +225,7 @@ impl ResponsesWebsocketConnection {
         let models_etag = self.models_etag.clone();
         let server_model = self.server_model.clone();
         let telemetry = self.telemetry.clone();
-        let request_body = serde_json::to_value(&request).map_err(|err| {
-            ApiError::Stream(format!("failed to encode websocket request: {err}"))
-        })?;
+        let request_text = serialize_websocket_request(&request)?;
 
         let current_span = Span::current();
         tokio::spawn(
@@ -261,7 +259,7 @@ impl ResponsesWebsocketConnection {
                     run_websocket_response_stream(
                         ws_stream,
                         tx_event.clone(),
-                        request_body,
+                        request_text,
                         idle_timeout,
                         telemetry,
                         connection_reused,
@@ -629,7 +627,7 @@ fn json_header_value(value: Value) -> Option<HeaderValue> {
 async fn run_websocket_response_stream(
     ws_stream: &mut WsStream,
     tx_event: mpsc::Sender<std::result::Result<ResponseEvent, ApiError>>,
-    request_body: Value,
+    request_text: String,
     idle_timeout: Duration,
     telemetry: Option<Arc<dyn WebsocketTelemetry>>,
     connection_reused: bool,
@@ -638,7 +636,7 @@ async fn run_websocket_response_stream(
     let mut last_server_model: Option<String> = None;
     send_websocket_request(
         ws_stream,
-        request_body,
+        request_text,
         idle_timeout,
         telemetry.as_ref(),
         connection_reused,
@@ -758,19 +756,11 @@ async fn run_websocket_response_stream(
 
 async fn send_websocket_request(
     ws_stream: &WsStream,
-    request_body: Value,
+    request_text: String,
     idle_timeout: Duration,
     telemetry: Option<&Arc<dyn WebsocketTelemetry>>,
     connection_reused: bool,
 ) -> Result<(), ApiError> {
-    let request_text = match serde_json::to_string(&request_body) {
-        Ok(text) => text,
-        Err(err) => {
-            return Err(ApiError::Stream(format!(
-                "failed to encode websocket request: {err}"
-            )));
-        }
-    };
     trace!("websocket request: {request_text}");
 
     let request_start = Instant::now();
@@ -797,11 +787,64 @@ async fn send_websocket_request(
     Ok(())
 }
 
+fn serialize_websocket_request(request: &ResponsesWsRequest) -> Result<String, ApiError> {
+    serde_json::to_string(request)
+        .map_err(|err| ApiError::Stream(format!("failed to encode websocket request: {err}")))
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;
+    use crate::common::ResponseCreateWsRequest;
+    use codex_protocol::models::ContentItem;
+    use codex_protocol::models::ResponseItem;
     use pretty_assertions::assert_eq;
     use serde_json::json;
+    use std::collections::HashMap;
+
+    #[test]
+    fn direct_serialization_preserves_websocket_request_payload() {
+        let request = ResponsesWsRequest::ResponseCreate(ResponseCreateWsRequest {
+            model: "gpt-test".to_string(),
+            instructions: "Use the available tools.".to_string(),
+            previous_response_id: Some("resp-1".to_string()),
+            input: vec![ResponseItem::Message {
+                id: Some("msg-1".to_string()),
+                role: "user".to_string(),
+                content: vec![ContentItem::InputText {
+                    text: "hello".to_string(),
+                }],
+                phase: None,
+            }],
+            tools: vec![json!({
+                "type": "function",
+                "name": "lookup",
+                "parameters": {"type": "object"}
+            })],
+            tool_choice: "auto".to_string(),
+            parallel_tool_calls: true,
+            reasoning: None,
+            store: false,
+            stream: true,
+            include: vec!["reasoning.encrypted_content".to_string()],
+            service_tier: Some("priority".to_string()),
+            prompt_cache_key: Some("cache-key".to_string()),
+            text: None,
+            generate: Some(false),
+            client_metadata: Some(HashMap::from([(
+                "traceparent".to_string(),
+                "00-0123456789abcdef0123456789abcdef-0123456789abcdef-01".to_string(),
+            )])),
+        });
+
+        let previous_payload = serde_json::to_value(&request).expect("serialize previous payload");
+        let request_text =
+            serialize_websocket_request(&request).expect("serialize websocket request");
+        let wire_payload =
+            serde_json::from_str::<Value>(&request_text).expect("parse websocket request");
+
+        assert_eq!(wire_payload, previous_payload);
+    }
 
     #[test]
     fn websocket_config_enables_permessage_deflate() {