Use model catalog default for reasoning summary fallback (openai#12873)

## Summary
- make `Config.model_reasoning_summary` optional so unset means use
model default
- resolve the optional config value to a concrete summary when building
`TurnContext`
- add protocol support for `default_reasoning_summary` in model metadata

## Validation
- `cargo test -p codex-core --lib client::tests -- --nocapture`

---------

Co-authored-by: Codex <noreply@openai.com>

Author: pakrym-oai

codex-rs/app-server/tests/common/models_cache.rs

@@ -1,6 +1,7 @@
 use chrono::DateTime;
 use chrono::Utc;
 use codex_core::test_support::all_model_presets;
+use codex_protocol::config_types::ReasoningSummary;
 use codex_protocol::openai_models::ConfigShellToolType;
 use codex_protocol::openai_models::ModelInfo;
 use codex_protocol::openai_models::ModelPreset;
@@ -30,6 +31,7 @@ fn preset_to_info(preset: &ModelPreset, priority: i32) -> ModelInfo {
         base_instructions: "base instructions".to_string(),
         model_messages: None,
         supports_reasoning_summaries: false,
+        default_reasoning_summary: ReasoningSummary::Auto,
         support_verbosity: false,
         default_verbosity: None,
         apply_patch_tool_type: None,

codex-rs/codex-api/tests/models_integration.rs

@@ -3,6 +3,7 @@ use codex_api::ModelsClient;
 use codex_api::provider::Provider;
 use codex_api::provider::RetryConfig;
 use codex_client::ReqwestTransport;
+use codex_protocol::config_types::ReasoningSummary;
 use codex_protocol::openai_models::ConfigShellToolType;
 use codex_protocol::openai_models::ModelInfo;
 use codex_protocol::openai_models::ModelVisibility;
@@ -78,6 +79,7 @@ async fn models_client_hits_models_endpoint() {
             base_instructions: "base instructions".to_string(),
             model_messages: None,
             supports_reasoning_summaries: false,
+            default_reasoning_summary: ReasoningSummary::Auto,
             support_verbosity: false,
             default_verbosity: None,
             apply_patch_tool_type: None,

codex-rs/core/src/codex.rs

@@ -754,7 +754,7 @@ pub(crate) struct SessionConfiguration {
     provider: ModelProviderInfo,
 
     collaboration_mode: CollaborationMode,
-    model_reasoning_summary: ReasoningSummaryConfig,
+    model_reasoning_summary: Option<ReasoningSummaryConfig>,
 
     /// Developer instructions that supplement the base instructions.
     developer_instructions: Option<String>,
@@ -824,7 +824,7 @@ impl SessionConfiguration {
             next_configuration.collaboration_mode = collaboration_mode;
         }
         if let Some(summary) = updates.reasoning_summary {
-            next_configuration.model_reasoning_summary = summary;
+            next_configuration.model_reasoning_summary = Some(summary);
         }
         if let Some(personality) = updates.personality {
             next_configuration.personality = Some(personality);
@@ -985,7 +985,9 @@ impl Session {
         skills_outcome: Arc<SkillLoadOutcome>,
     ) -> TurnContext {
         let reasoning_effort = session_configuration.collaboration_mode.reasoning_effort();
-        let reasoning_summary = session_configuration.model_reasoning_summary;
+        let reasoning_summary = session_configuration
+            .model_reasoning_summary
+            .unwrap_or(model_info.default_reasoning_summary);
         let otel_manager = otel_manager.clone().with_model(
             session_configuration.collaboration_mode.model(),
             model_info.slug.as_str(),
@@ -1271,7 +1273,9 @@ impl Session {
         otel_manager.conversation_starts(
             config.model_provider.name.as_str(),
             session_configuration.collaboration_mode.reasoning_effort(),
-            config.model_reasoning_summary,
+            config
+                .model_reasoning_summary
+                .unwrap_or(ReasoningSummaryConfig::Auto),
             config.model_context_window,
             config.model_auto_compact_token_limit,
             config.permissions.approval_policy.value(),
@@ -4635,7 +4639,9 @@ async fn spawn_review_thread(
     let provider_for_context = provider.clone();
     let otel_manager_for_context = otel_manager.clone();
     let reasoning_effort = per_turn_config.model_reasoning_effort;
-    let reasoning_summary = per_turn_config.model_reasoning_summary;
+    let reasoning_summary = per_turn_config
+        .model_reasoning_summary
+        .unwrap_or(model_info.default_reasoning_summary);
     let session_source = parent_turn_context.session_source.clone();
 
     let per_turn_config = Arc::new(per_turn_config);

codex-rs/core/src/config/mod.rs

@@ -412,9 +412,9 @@ pub struct Config {
     /// global default").
     pub plan_mode_reasoning_effort: Option<ReasoningEffort>,
 
-    /// If not "none", the value to use for `reasoning.summary` when making a
-    /// request using the Responses API.
-    pub model_reasoning_summary: ReasoningSummary,
+    /// Optional value to use for `reasoning.summary` when making a request
+    /// using the Responses API. When unset, the model catalog default is used.
+    pub model_reasoning_summary: Option<ReasoningSummary>,
 
     /// Optional override to force-enable reasoning summaries for the configured model.
     pub model_supports_reasoning_summaries: Option<bool>,
@@ -2141,8 +2141,7 @@ impl Config {
                 .or(cfg.plan_mode_reasoning_effort),
             model_reasoning_summary: config_profile
                 .model_reasoning_summary
-                .or(cfg.model_reasoning_summary)
-                .unwrap_or_default(),
+                .or(cfg.model_reasoning_summary),
             model_supports_reasoning_summaries: cfg.model_supports_reasoning_summaries,
             model_catalog,
             model_verbosity: config_profile.model_verbosity.or(cfg.model_verbosity),
@@ -4764,7 +4763,7 @@ model_verbosity = "high"
                 show_raw_agent_reasoning: false,
                 model_reasoning_effort: Some(ReasoningEffort::High),
                 plan_mode_reasoning_effort: None,
-                model_reasoning_summary: ReasoningSummary::Detailed,
+                model_reasoning_summary: Some(ReasoningSummary::Detailed),
                 model_supports_reasoning_summaries: None,
                 model_catalog: None,
                 model_verbosity: None,
@@ -4890,7 +4889,7 @@ model_verbosity = "high"
             show_raw_agent_reasoning: false,
             model_reasoning_effort: None,
             plan_mode_reasoning_effort: None,
-            model_reasoning_summary: ReasoningSummary::default(),
+            model_reasoning_summary: None,
             model_supports_reasoning_summaries: None,
             model_catalog: None,
             model_verbosity: None,
@@ -5014,7 +5013,7 @@ model_verbosity = "high"
             show_raw_agent_reasoning: false,
             model_reasoning_effort: None,
             plan_mode_reasoning_effort: None,
-            model_reasoning_summary: ReasoningSummary::default(),
+            model_reasoning_summary: None,
             model_supports_reasoning_summaries: None,
             model_catalog: None,
             model_verbosity: None,
@@ -5124,7 +5123,7 @@ model_verbosity = "high"
             show_raw_agent_reasoning: false,
             model_reasoning_effort: Some(ReasoningEffort::High),
             plan_mode_reasoning_effort: None,
-            model_reasoning_summary: ReasoningSummary::Detailed,
+            model_reasoning_summary: Some(ReasoningSummary::Detailed),
             model_supports_reasoning_summaries: None,
             model_catalog: None,
             model_verbosity: Some(Verbosity::High),

codex-rs/core/src/models_manager/model_info.rs

@@ -1,3 +1,4 @@
+use codex_protocol::config_types::ReasoningSummary;
 use codex_protocol::openai_models::ConfigShellToolType;
 use codex_protocol::openai_models::ModelInfo;
 use codex_protocol::openai_models::ModelInstructionsVariables;
@@ -72,6 +73,7 @@ pub(crate) fn model_info_from_slug(slug: &str) -> ModelInfo {
         base_instructions: BASE_INSTRUCTIONS.to_string(),
         model_messages: local_personality_messages_for_slug(slug),
         supports_reasoning_summaries: false,
+        default_reasoning_summary: ReasoningSummary::Auto,
         support_verbosity: false,
         default_verbosity: None,
         apply_patch_tool_type: None,

codex-rs/core/src/tools/handlers/multi_agents.rs

@@ -914,7 +914,7 @@ fn build_agent_shared_config(turn: &TurnContext) -> Result<Config, FunctionCallE
     config.model = Some(turn.model_info.slug.clone());
     config.model_provider = turn.provider.clone();
     config.model_reasoning_effort = turn.reasoning_effort;
-    config.model_reasoning_summary = turn.reasoning_summary;
+    config.model_reasoning_summary = Some(turn.reasoning_summary);
     config.developer_instructions = turn.developer_instructions.clone();
     config.compact_prompt = turn.compact_prompt.clone();
     apply_spawn_agent_runtime_overrides(&mut config, turn)?;
@@ -2046,7 +2046,7 @@ mod tests {
         expected.model = Some(turn.model_info.slug.clone());
         expected.model_provider = turn.provider.clone();
         expected.model_reasoning_effort = turn.reasoning_effort;
-        expected.model_reasoning_summary = turn.reasoning_summary;
+        expected.model_reasoning_summary = Some(turn.reasoning_summary);
         expected.developer_instructions = turn.developer_instructions.clone();
         expected.compact_prompt = turn.compact_prompt.clone();
         expected.permissions.shell_environment_policy = turn.shell_environment_policy.clone();
@@ -2098,7 +2098,7 @@ mod tests {
         expected.model = Some(turn.model_info.slug.clone());
         expected.model_provider = turn.provider.clone();
         expected.model_reasoning_effort = turn.reasoning_effort;
-        expected.model_reasoning_summary = turn.reasoning_summary;
+        expected.model_reasoning_summary = Some(turn.reasoning_summary);
         expected.developer_instructions = turn.developer_instructions.clone();
         expected.compact_prompt = turn.compact_prompt.clone();
         expected.permissions.shell_environment_policy = turn.shell_environment_policy.clone();

codex-rs/core/tests/responses_headers.rs

@@ -111,7 +111,14 @@ async fn responses_stream_includes_subagent_header_on_review() {
     }];
 
     let mut stream = client_session
-        .stream(&prompt, &model_info, &otel_manager, effort, summary, None)
+        .stream(
+            &prompt,
+            &model_info,
+            &otel_manager,
+            effort,
+            summary.unwrap_or(model_info.default_reasoning_summary),
+            None,
+        )
         .await
         .expect("stream failed");
     while let Some(event) = stream.next().await {
@@ -216,7 +223,14 @@ async fn responses_stream_includes_subagent_header_on_other() {
     }];
 
     let mut stream = client_session
-        .stream(&prompt, &model_info, &otel_manager, effort, summary, None)
+        .stream(
+            &prompt,
+            &model_info,
+            &otel_manager,
+            effort,
+            summary.unwrap_or(model_info.default_reasoning_summary),
+            None,
+        )
         .await
         .expect("stream failed");
     while let Some(event) = stream.next().await {
@@ -267,7 +281,7 @@ async fn responses_respects_model_info_overrides_from_config() {
     config.model_provider_id = provider.name.clone();
     config.model_provider = provider.clone();
     config.model_supports_reasoning_summaries = Some(true);
-    config.model_reasoning_summary = ReasoningSummary::Detailed;
+    config.model_reasoning_summary = Some(ReasoningSummary::Detailed);
     let effort = config.model_reasoning_effort;
     let summary = config.model_reasoning_summary;
     let model = config.model.clone().expect("model configured");
@@ -320,7 +334,14 @@ async fn responses_respects_model_info_overrides_from_config() {
     }];
 
     let mut stream = client_session
-        .stream(&prompt, &model_info, &otel_manager, effort, summary, None)
+        .stream(
+            &prompt,
+            &model_info,
+            &otel_manager,
+            effort,
+            summary.unwrap_or(model_info.default_reasoning_summary),
+            None,
+        )
         .await
         .expect("stream failed");
     while let Some(event) = stream.next().await {

codex-rs/core/tests/suite/client.rs

@@ -31,6 +31,7 @@ use codex_protocol::models::ReasoningItemContent;
 use codex_protocol::models::ReasoningItemReasoningSummary;
 use codex_protocol::models::ResponseItem;
 use codex_protocol::models::WebSearchAction;
+use codex_protocol::openai_models::ModelsResponse;
 use codex_protocol::openai_models::ReasoningEffort;
 use codex_protocol::protocol::EventMsg;
 use codex_protocol::protocol::Op;
@@ -980,7 +981,9 @@ async fn user_turn_collaboration_mode_overrides_model_and_effort() -> anyhow::Re
             sandbox_policy: config.permissions.sandbox_policy.get().clone(),
             model: session_configured.model.clone(),
             effort: Some(ReasoningEffort::Low),
-            summary: config.model_reasoning_summary,
+            summary: config
+                .model_reasoning_summary
+                .unwrap_or(ReasoningSummary::Auto),
             collaboration_mode: Some(collaboration_mode),
             final_output_json_schema: None,
             personality: None,
@@ -1014,7 +1017,7 @@ async fn configured_reasoning_summary_is_sent() -> anyhow::Result<()> {
     .await;
     let TestCodex { codex, .. } = test_codex()
         .with_config(|config| {
-            config.model_reasoning_summary = ReasoningSummary::Concise;
+            config.model_reasoning_summary = Some(ReasoningSummary::Concise);
         })
         .build(&server)
         .await?;
@@ -1058,7 +1061,7 @@ async fn reasoning_summary_is_omitted_when_disabled() -> anyhow::Result<()> {
     .await;
     let TestCodex { codex, .. } = test_codex()
         .with_config(|config| {
-            config.model_reasoning_summary = ReasoningSummary::None;
+            config.model_reasoning_summary = Some(ReasoningSummary::None);
         })
         .build(&server)
         .await?;
@@ -1089,6 +1092,60 @@ async fn reasoning_summary_is_omitted_when_disabled() -> anyhow::Result<()> {
     Ok(())
 }
 
+#[tokio::test(flavor = "multi_thread", worker_threads = 2)]
+async fn reasoning_summary_none_overrides_model_catalog_default() -> anyhow::Result<()> {
+    skip_if_no_network!(Ok(()));
+    let server = MockServer::start().await;
+
+    let resp_mock = mount_sse_once(
+        &server,
+        sse(vec![ev_response_created("resp1"), ev_completed("resp1")]),
+    )
+    .await;
+
+    let mut model_catalog: ModelsResponse =
+        serde_json::from_str(include_str!("../../models.json")).expect("valid models.json");
+    let model = model_catalog
+        .models
+        .iter_mut()
+        .find(|model| model.slug == "gpt-5.1")
+        .expect("gpt-5.1 exists in bundled models.json");
+    model.supports_reasoning_summaries = true;
+    model.default_reasoning_summary = ReasoningSummary::Detailed;
+
+    let TestCodex { codex, .. } = test_codex()
+        .with_model("gpt-5.1")
+        .with_config(move |config| {
+            config.model_reasoning_summary = Some(ReasoningSummary::None);
+            config.model_catalog = Some(model_catalog);
+        })
+        .build(&server)
+        .await?;
+
+    codex
+        .submit(Op::UserInput {
+            items: vec![UserInput::Text {
+                text: "hello".into(),
+                text_elements: Vec::new(),
+            }],
+            final_output_json_schema: None,
+        })
+        .await
+        .unwrap();
+
+    wait_for_event(&codex, |ev| matches!(ev, EventMsg::TurnComplete(_))).await;
+
+    let request_body = resp_mock.single_request().body_json();
+    pretty_assertions::assert_eq!(
+        request_body
+            .get("reasoning")
+            .and_then(|reasoning| reasoning.get("summary")),
+        None
+    );
+
+    Ok(())
+}
+
 #[tokio::test(flavor = "multi_thread", worker_threads = 2)]
 async fn includes_default_verbosity_in_request() -> anyhow::Result<()> {
     skip_if_no_network!(Ok(()));
@@ -1441,7 +1498,14 @@ async fn azure_responses_request_includes_store_and_reasoning_ids() {
     });
 
     let mut stream = client_session
-        .stream(&prompt, &model_info, &otel_manager, effort, summary, None)
+        .stream(
+            &prompt,
+            &model_info,
+            &otel_manager,
+            effort,
+            summary.unwrap_or(ReasoningSummary::Auto),
+            None,
+        )
         .await
         .expect("responses stream to start");
 

codex-rs/core/tests/suite/collaboration_instructions.rs

@@ -169,7 +169,10 @@ async fn collaboration_instructions_added_on_user_turn() -> Result<()> {
             sandbox_policy: test.config.permissions.sandbox_policy.get().clone(),
             model: test.session_configured.model.clone(),
             effort: None,
-            summary: test.config.model_reasoning_summary,
+            summary: test
+                .config
+                .model_reasoning_summary
+                .unwrap_or(codex_protocol::config_types::ReasoningSummary::Auto),
             collaboration_mode: Some(collaboration_mode),
             final_output_json_schema: None,
             personality: None,
@@ -275,7 +278,10 @@ async fn user_turn_overrides_collaboration_instructions_after_override() -> Resu
             sandbox_policy: test.config.permissions.sandbox_policy.get().clone(),
             model: test.session_configured.model.clone(),
             effort: None,
-            summary: test.config.model_reasoning_summary,
+            summary: test
+                .config
+                .model_reasoning_summary
+                .unwrap_or(codex_protocol::config_types::ReasoningSummary::Auto),
             collaboration_mode: Some(turn_mode),
             final_output_json_schema: None,
             personality: None,

codex-rs/core/tests/suite/model_switching.rs

@@ -234,6 +234,7 @@ async fn model_change_from_image_to_text_strips_prior_image_content() -> Result<
         base_instructions: "base instructions".to_string(),
         model_messages: None,
         supports_reasoning_summaries: false,
+        default_reasoning_summary: ReasoningSummary::Auto,
         support_verbosity: false,
         default_verbosity: None,
         apply_patch_tool_type: None,
@@ -391,6 +392,7 @@ async fn model_switch_to_smaller_model_updates_token_context_window() -> Result<
         base_instructions: "base instructions".to_string(),
         model_messages: None,
         supports_reasoning_summaries: false,
+        default_reasoning_summary: ReasoningSummary::Auto,
         support_verbosity: false,
         default_verbosity: None,
         apply_patch_tool_type: None,