diff --git a/codex-rs/core/src/client_common.rs b/codex-rs/core/src/client_common.rs
index 5aa0d8cf..fd894a63 100644
--- a/codex-rs/core/src/client_common.rs
+++ b/codex-rs/core/src/client_common.rs
@@ -84,8 +84,10 @@ pub enum ResponseEvent {
 
 #[derive(Debug, Serialize)]
 pub(crate) struct Reasoning {
-    pub(crate) effort: ReasoningEffortConfig,
-    pub(crate) summary: ReasoningSummaryConfig,
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub(crate) effort: Option<ReasoningEffortConfig>,
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub(crate) summary: Option<ReasoningSummaryConfig>,
 }
 
 /// Controls under the `text` field in the Responses API for GPT-5.
@@ -146,7 +148,10 @@ pub(crate) fn create_reasoning_param_for_request(
         return None;
     }
 
-    effort.map(|effort| Reasoning { effort, summary })
+    Some(Reasoning {
+        effort,
+        summary: Some(summary),
+    })
 }
 
 pub(crate) fn create_text_param_for_request(
diff --git a/codex-rs/core/tests/suite/client.rs b/codex-rs/core/tests/suite/client.rs
index 23278807..8360a836 100644
--- a/codex-rs/core/tests/suite/client.rs
+++ b/codex-rs/core/tests/suite/client.rs
@@ -450,7 +450,6 @@ async fn chatgpt_auth_sends_correct_request() {
     // Init session
     let codex_home = TempDir::new().unwrap();
     let mut config = load_default_config_for_test(&codex_home);
-    let include_reasoning = config.model_reasoning_effort.is_some();
     config.model_provider = model_provider;
     let conversation_manager = ConversationManager::with_auth(create_dummy_codex_auth());
     let NewConversation {
@@ -492,18 +491,10 @@ async fn chatgpt_auth_sends_correct_request() {
     );
     assert_eq!(request_chatgpt_account_id.to_str().unwrap(), "account_id");
     assert!(request_body["stream"].as_bool().unwrap());
-    if include_reasoning {
-        assert_eq!(
-            request_body["include"][0].as_str().unwrap(),
-            "reasoning.encrypted_content"
-        );
-    } else {
-        assert!(
-            request_body["include"]
-                .as_array()
-                .is_none_or(|items| items.is_empty())
-        );
-    }
+    assert_eq!(
+        request_body["include"][0].as_str().unwrap(),
+        "reasoning.encrypted_content"
+    );
 }
 
 #[tokio::test(flavor = "multi_thread", worker_threads = 2)]