diff --git a/codex-rs/core/src/client.rs b/codex-rs/core/src/client.rs
index 438c7c5eeee..326d81e0e91 100644
--- a/codex-rs/core/src/client.rs
+++ b/codex-rs/core/src/client.rs
@@ -31,6 +31,7 @@ use codex_otel::OtelManager;
 
 use codex_protocol::ThreadId;
 use codex_protocol::config_types::ReasoningSummary as ReasoningSummaryConfig;
+use codex_protocol::config_types::WebSearchMode;
 use codex_protocol::models::ResponseItem;
 use codex_protocol::openai_models::ModelInfo;
 use codex_protocol::openai_models::ReasoningEffort as ReasoningEffortConfig;
@@ -64,6 +65,8 @@ use crate::model_provider_info::WireApi;
 use crate::tools::spec::create_tools_json_for_chat_completions_api;
 use crate::tools::spec::create_tools_json_for_responses_api;
 
+pub const WEB_SEARCH_ELIGIBLE_HEADER: &str = "x-oai-web-search-eligible";
+
 #[derive(Debug)]
 struct ModelClientState {
     config: Arc<Config>,
@@ -319,7 +322,7 @@ impl ModelClientSession {
             store_override: None,
             conversation_id: Some(conversation_id),
             session_source: Some(self.state.session_source.clone()),
-            extra_headers: beta_feature_headers(&self.state.config),
+            extra_headers: build_responses_headers(&self.state.config),
             compression,
         }
     }
@@ -635,6 +638,21 @@ fn beta_feature_headers(config: &Config) -> ApiHeaderMap {
     headers
 }
 
+fn build_responses_headers(config: &Config) -> ApiHeaderMap {
+    let mut headers = beta_feature_headers(config);
+    headers.insert(
+        WEB_SEARCH_ELIGIBLE_HEADER,
+        HeaderValue::from_static(
+            if matches!(config.web_search_mode, Some(WebSearchMode::Disabled)) {
+                "false"
+            } else {
+                "true"
+            },
+        ),
+    );
+    headers
+}
+
 fn map_response_stream<S>(api_stream: S, otel_manager: OtelManager) -> ResponseStream
 where
     S: futures::Stream<Item = std::result::Result<ResponseEvent, ApiError>>
diff --git a/codex-rs/core/src/codex.rs b/codex-rs/core/src/codex.rs
index 158443ee49f..e54e997d168 100644
--- a/codex-rs/core/src/codex.rs
+++ b/codex-rs/core/src/codex.rs
@@ -2416,7 +2416,7 @@ async fn spawn_review_thread(
     let tools_config = ToolsConfig::new(&ToolsConfigParams {
         model_info: &review_model_info,
         features: &review_features,
-        web_search_mode: review_web_search_mode,
+        web_search_mode: Some(review_web_search_mode),
     });
 
     let base_instructions = REVIEW_PROMPT.to_string();
@@ -2429,7 +2429,7 @@ async fn spawn_review_thread(
     let mut per_turn_config = (*config).clone();
     per_turn_config.model = Some(model.clone());
     per_turn_config.features = review_features.clone();
-    per_turn_config.web_search_mode = review_web_search_mode;
+    per_turn_config.web_search_mode = Some(review_web_search_mode);
 
     let otel_manager = parent_turn_context
         .client
diff --git a/codex-rs/core/src/config/mod.rs b/codex-rs/core/src/config/mod.rs
index 5e5d26c791a..034783da15b 100644
--- a/codex-rs/core/src/config/mod.rs
+++ b/codex-rs/core/src/config/mod.rs
@@ -337,7 +337,8 @@ pub struct Config {
     /// model info's default preference.
     pub include_apply_patch_tool: bool,
 
-    pub web_search_mode: WebSearchMode,
+    /// Explicit or feature-derived web search mode.
+    pub web_search_mode: Option<WebSearchMode>,
 
     /// If set to `true`, used only the experimental unified exec tool.
     pub use_experimental_unified_exec_tool: bool,
@@ -1182,24 +1183,22 @@ pub fn resolve_oss_provider(
     }
 }
 
-/// Resolve the web search mode from the config, profile, and features.
+/// Resolve the web search mode from explicit config and feature flags.
 fn resolve_web_search_mode(
     config_toml: &ConfigToml,
     config_profile: &ConfigProfile,
     features: &Features,
-) -> WebSearchMode {
-    // Enum gets precedence over features flags
+) -> Option<WebSearchMode> {
     if let Some(mode) = config_profile.web_search.or(config_toml.web_search) {
-        return mode;
+        return Some(mode);
     }
     if features.enabled(Feature::WebSearchCached) {
-        return WebSearchMode::Cached;
+        return Some(WebSearchMode::Cached);
     }
     if features.enabled(Feature::WebSearchRequest) {
-        return WebSearchMode::Live;
+        return Some(WebSearchMode::Live);
     }
-    // Fall back to default
-    WebSearchMode::default()
+    None
 }
 
 impl Config {
@@ -2202,15 +2201,12 @@ trust_level = "trusted"
     }
 
     #[test]
-    fn web_search_mode_uses_default_if_unset() {
+    fn web_search_mode_uses_none_if_unset() {
         let cfg = ConfigToml::default();
         let profile = ConfigProfile::default();
         let features = Features::with_defaults();
 
-        assert_eq!(
-            resolve_web_search_mode(&cfg, &profile, &features),
-            WebSearchMode::default()
-        );
+        assert_eq!(resolve_web_search_mode(&cfg, &profile, &features), None);
     }
 
     #[test]
@@ -2225,7 +2221,7 @@ trust_level = "trusted"
 
         assert_eq!(
             resolve_web_search_mode(&cfg, &profile, &features),
-            WebSearchMode::Live
+            Some(WebSearchMode::Live)
         );
     }
 
@@ -2241,7 +2237,7 @@ trust_level = "trusted"
 
         assert_eq!(
             resolve_web_search_mode(&cfg, &profile, &features),
-            WebSearchMode::Disabled
+            Some(WebSearchMode::Disabled)
         );
     }
 
@@ -3581,7 +3577,7 @@ model_verbosity = "high"
                 forced_chatgpt_workspace_id: None,
                 forced_login_method: None,
                 include_apply_patch_tool: false,
-                web_search_mode: WebSearchMode::default(),
+                web_search_mode: None,
                 use_experimental_unified_exec_tool: false,
                 ghost_snapshot: GhostSnapshotConfig::default(),
                 features: Features::with_defaults(),
@@ -3668,7 +3664,7 @@ model_verbosity = "high"
             forced_chatgpt_workspace_id: None,
             forced_login_method: None,
             include_apply_patch_tool: false,
-            web_search_mode: WebSearchMode::default(),
+            web_search_mode: None,
             use_experimental_unified_exec_tool: false,
             ghost_snapshot: GhostSnapshotConfig::default(),
             features: Features::with_defaults(),
@@ -3770,7 +3766,7 @@ model_verbosity = "high"
             forced_chatgpt_workspace_id: None,
             forced_login_method: None,
             include_apply_patch_tool: false,
-            web_search_mode: WebSearchMode::default(),
+            web_search_mode: None,
             use_experimental_unified_exec_tool: false,
             ghost_snapshot: GhostSnapshotConfig::default(),
             features: Features::with_defaults(),
@@ -3858,7 +3854,7 @@ model_verbosity = "high"
             forced_chatgpt_workspace_id: None,
             forced_login_method: None,
             include_apply_patch_tool: false,
-            web_search_mode: WebSearchMode::default(),
+            web_search_mode: None,
             use_experimental_unified_exec_tool: false,
             ghost_snapshot: GhostSnapshotConfig::default(),
             features: Features::with_defaults(),
diff --git a/codex-rs/core/src/lib.rs b/codex-rs/core/src/lib.rs
index 4c6183454d9..498c45748fd 100644
--- a/codex-rs/core/src/lib.rs
+++ b/codex-rs/core/src/lib.rs
@@ -111,6 +111,7 @@ mod user_shell_command;
 pub mod util;
 
 pub use apply_patch::CODEX_APPLY_PATCH_ARG1;
+pub use client::WEB_SEARCH_ELIGIBLE_HEADER;
 pub use command_safety::is_dangerous_command;
 pub use command_safety::is_safe_command;
 pub use exec_policy::ExecPolicyError;
diff --git a/codex-rs/core/src/tasks/review.rs b/codex-rs/core/src/tasks/review.rs
index 353189a6be9..9157e922ecf 100644
--- a/codex-rs/core/src/tasks/review.rs
+++ b/codex-rs/core/src/tasks/review.rs
@@ -86,7 +86,7 @@ async fn start_review_conversation(
     let mut sub_agent_config = config.as_ref().clone();
     // Carry over review-only feature restrictions so the delegate cannot
     // re-enable blocked tools (web search, view image).
-    sub_agent_config.web_search_mode = WebSearchMode::Disabled;
+    sub_agent_config.web_search_mode = Some(WebSearchMode::Disabled);
 
     // Set explicit review rubric for the sub-agent
     sub_agent_config.base_instructions = Some(crate::REVIEW_PROMPT.to_string());
diff --git a/codex-rs/core/src/tools/spec.rs b/codex-rs/core/src/tools/spec.rs
index 28fc3a17017..345f6b6ebef 100644
--- a/codex-rs/core/src/tools/spec.rs
+++ b/codex-rs/core/src/tools/spec.rs
@@ -24,7 +24,7 @@ use std::collections::HashMap;
 pub(crate) struct ToolsConfig {
     pub shell_type: ConfigShellToolType,
     pub apply_patch_tool_type: Option<ApplyPatchToolType>,
-    pub web_search_mode: WebSearchMode,
+    pub web_search_mode: Option<WebSearchMode>,
     pub collab_tools: bool,
     pub experimental_supported_tools: Vec<String>,
 }
@@ -32,7 +32,7 @@ pub(crate) struct ToolsConfig {
 pub(crate) struct ToolsConfigParams<'a> {
     pub(crate) model_info: &'a ModelInfo,
     pub(crate) features: &'a Features,
-    pub(crate) web_search_mode: WebSearchMode,
+    pub(crate) web_search_mode: Option<WebSearchMode>,
 }
 
 impl ToolsConfig {
@@ -1225,17 +1225,17 @@ pub(crate) fn build_specs(
     }
 
     match config.web_search_mode {
-        WebSearchMode::Disabled => {}
-        WebSearchMode::Cached => {
+        Some(WebSearchMode::Cached) => {
             builder.push_spec(ToolSpec::WebSearch {
                 external_web_access: Some(false),
             });
         }
-        WebSearchMode::Live => {
+        Some(WebSearchMode::Live) => {
             builder.push_spec(ToolSpec::WebSearch {
                 external_web_access: Some(true),
             });
         }
+        Some(WebSearchMode::Disabled) | None => {}
     }
 
     builder.push_spec_with_parallel_support(create_view_image_tool(), true);
@@ -1379,7 +1379,7 @@ mod tests {
         let config = ToolsConfig::new(&ToolsConfigParams {
             model_info: &model_info,
             features: &features,
-            web_search_mode: WebSearchMode::Live,
+            web_search_mode: Some(WebSearchMode::Live),
         });
         let (tools, _) = build_specs(&config, None).build();
 
@@ -1441,7 +1441,7 @@ mod tests {
         let tools_config = ToolsConfig::new(&ToolsConfigParams {
             model_info: &model_info,
             features: &features,
-            web_search_mode: WebSearchMode::Cached,
+            web_search_mode: Some(WebSearchMode::Cached),
         });
         let (tools, _) = build_specs(&tools_config, None).build();
         assert_contains_tool_names(
@@ -1453,7 +1453,7 @@ mod tests {
     fn assert_model_tools(
         model_slug: &str,
         features: &Features,
-        web_search_mode: WebSearchMode,
+        web_search_mode: Option<WebSearchMode>,
         expected_tools: &[&str],
     ) {
         let config = test_config();
@@ -1477,7 +1477,7 @@ mod tests {
         let tools_config = ToolsConfig::new(&ToolsConfigParams {
             model_info: &model_info,
             features: &features,
-            web_search_mode: WebSearchMode::Cached,
+            web_search_mode: Some(WebSearchMode::Cached),
         });
         let (tools, _) = build_specs(&tools_config, None).build();
 
@@ -1499,7 +1499,7 @@ mod tests {
         let tools_config = ToolsConfig::new(&ToolsConfigParams {
             model_info: &model_info,
             features: &features,
-            web_search_mode: WebSearchMode::Live,
+            web_search_mode: Some(WebSearchMode::Live),
         });
         let (tools, _) = build_specs(&tools_config, None).build();
 
@@ -1517,7 +1517,7 @@ mod tests {
         assert_model_tools(
             "gpt-5-codex",
             &Features::with_defaults(),
-            WebSearchMode::Cached,
+            Some(WebSearchMode::Cached),
             &[
                 "shell_command",
                 "list_mcp_resources",
@@ -1536,7 +1536,7 @@ mod tests {
         assert_model_tools(
             "gpt-5.1-codex",
             &Features::with_defaults(),
-            WebSearchMode::Cached,
+            Some(WebSearchMode::Cached),
             &[
                 "shell_command",
                 "list_mcp_resources",
@@ -1555,7 +1555,7 @@ mod tests {
         assert_model_tools(
             "gpt-5-codex",
             Features::with_defaults().enable(Feature::UnifiedExec),
-            WebSearchMode::Live,
+            Some(WebSearchMode::Live),
             &[
                 "exec_command",
                 "write_stdin",
@@ -1575,7 +1575,7 @@ mod tests {
         assert_model_tools(
             "gpt-5.1-codex",
             Features::with_defaults().enable(Feature::UnifiedExec),
-            WebSearchMode::Live,
+            Some(WebSearchMode::Live),
             &[
                 "exec_command",
                 "write_stdin",
@@ -1595,7 +1595,7 @@ mod tests {
         assert_model_tools(
             "codex-mini-latest",
             &Features::with_defaults(),
-            WebSearchMode::Cached,
+            Some(WebSearchMode::Cached),
             &[
                 "local_shell",
                 "list_mcp_resources",
@@ -1613,7 +1613,7 @@ mod tests {
         assert_model_tools(
             "gpt-5.1-codex-mini",
             &Features::with_defaults(),
-            WebSearchMode::Cached,
+            Some(WebSearchMode::Cached),
             &[
                 "shell_command",
                 "list_mcp_resources",
@@ -1632,7 +1632,7 @@ mod tests {
         assert_model_tools(
             "gpt-5",
             &Features::with_defaults(),
-            WebSearchMode::Cached,
+            Some(WebSearchMode::Cached),
             &[
                 "shell",
                 "list_mcp_resources",
@@ -1650,7 +1650,7 @@ mod tests {
         assert_model_tools(
             "gpt-5.1",
             &Features::with_defaults(),
-            WebSearchMode::Cached,
+            Some(WebSearchMode::Cached),
             &[
                 "shell_command",
                 "list_mcp_resources",
@@ -1669,7 +1669,7 @@ mod tests {
         assert_model_tools(
             "exp-5.1",
             &Features::with_defaults(),
-            WebSearchMode::Cached,
+            Some(WebSearchMode::Cached),
             &[
                 "exec_command",
                 "write_stdin",
@@ -1689,7 +1689,7 @@ mod tests {
         assert_model_tools(
             "codex-mini-latest",
             Features::with_defaults().enable(Feature::UnifiedExec),
-            WebSearchMode::Live,
+            Some(WebSearchMode::Live),
             &[
                 "exec_command",
                 "write_stdin",
@@ -1712,7 +1712,7 @@ mod tests {
         let tools_config = ToolsConfig::new(&ToolsConfigParams {
             model_info: &model_info,
             features: &features,
-            web_search_mode: WebSearchMode::Live,
+            web_search_mode: Some(WebSearchMode::Live),
         });
         let (tools, _) = build_specs(&tools_config, Some(HashMap::new())).build();
 
@@ -1734,7 +1734,7 @@ mod tests {
         let tools_config = ToolsConfig::new(&ToolsConfigParams {
             model_info: &model_info,
             features: &features,
-            web_search_mode: WebSearchMode::Cached,
+            web_search_mode: Some(WebSearchMode::Cached),
         });
         let (tools, _) = build_specs(&tools_config, None).build();
 
@@ -1753,7 +1753,7 @@ mod tests {
         let tools_config = ToolsConfig::new(&ToolsConfigParams {
             model_info: &model_info,
             features: &features,
-            web_search_mode: WebSearchMode::Cached,
+            web_search_mode: Some(WebSearchMode::Cached),
         });
         let (tools, _) = build_specs(&tools_config, None).build();
 
@@ -1784,7 +1784,7 @@ mod tests {
         let tools_config = ToolsConfig::new(&ToolsConfigParams {
             model_info: &model_info,
             features: &features,
-            web_search_mode: WebSearchMode::Live,
+            web_search_mode: Some(WebSearchMode::Live),
         });
         let (tools, _) = build_specs(
             &tools_config,
@@ -1879,7 +1879,7 @@ mod tests {
         let tools_config = ToolsConfig::new(&ToolsConfigParams {
             model_info: &model_info,
             features: &features,
-            web_search_mode: WebSearchMode::Cached,
+            web_search_mode: Some(WebSearchMode::Cached),
         });
 
         // Intentionally construct a map with keys that would sort alphabetically.
@@ -1956,7 +1956,7 @@ mod tests {
         let tools_config = ToolsConfig::new(&ToolsConfigParams {
             model_info: &model_info,
             features: &features,
-            web_search_mode: WebSearchMode::Cached,
+            web_search_mode: Some(WebSearchMode::Cached),
         });
 
         let (tools, _) = build_specs(
@@ -2013,7 +2013,7 @@ mod tests {
         let tools_config = ToolsConfig::new(&ToolsConfigParams {
             model_info: &model_info,
             features: &features,
-            web_search_mode: WebSearchMode::Cached,
+            web_search_mode: Some(WebSearchMode::Cached),
         });
 
         let (tools, _) = build_specs(
@@ -2067,7 +2067,7 @@ mod tests {
         let tools_config = ToolsConfig::new(&ToolsConfigParams {
             model_info: &model_info,
             features: &features,
-            web_search_mode: WebSearchMode::Cached,
+            web_search_mode: Some(WebSearchMode::Cached),
         });
 
         let (tools, _) = build_specs(
@@ -2123,7 +2123,7 @@ mod tests {
         let tools_config = ToolsConfig::new(&ToolsConfigParams {
             model_info: &model_info,
             features: &features,
-            web_search_mode: WebSearchMode::Cached,
+            web_search_mode: Some(WebSearchMode::Cached),
         });
 
         let (tools, _) = build_specs(
@@ -2235,7 +2235,7 @@ Examples of valid command strings:
         let tools_config = ToolsConfig::new(&ToolsConfigParams {
             model_info: &model_info,
             features: &features,
-            web_search_mode: WebSearchMode::Cached,
+            web_search_mode: Some(WebSearchMode::Cached),
         });
         let (tools, _) = build_specs(
             &tools_config,
diff --git a/codex-rs/core/tests/responses_headers.rs b/codex-rs/core/tests/responses_headers.rs
index 8be6e363405..8eba3eabe71 100644
--- a/codex-rs/core/tests/responses_headers.rs
+++ b/codex-rs/core/tests/responses_headers.rs
@@ -9,15 +9,18 @@ use codex_core::ModelProviderInfo;
 use codex_core::Prompt;
 use codex_core::ResponseEvent;
 use codex_core::ResponseItem;
+use codex_core::WEB_SEARCH_ELIGIBLE_HEADER;
 use codex_core::WireApi;
 use codex_core::models_manager::manager::ModelsManager;
 use codex_otel::OtelManager;
 use codex_protocol::ThreadId;
 use codex_protocol::config_types::ReasoningSummary;
+use codex_protocol::config_types::WebSearchMode;
 use codex_protocol::protocol::SessionSource;
 use codex_protocol::protocol::SubAgentSource;
 use core_test_support::load_default_config_for_test;
 use core_test_support::responses;
+use core_test_support::test_codex::test_codex;
 use futures::StreamExt;
 use tempfile::TempDir;
 use wiremock::matchers::header;
@@ -213,6 +216,66 @@ async fn responses_stream_includes_subagent_header_on_other() {
     );
 }
 
+#[tokio::test]
+async fn responses_stream_includes_web_search_eligible_header_true_by_default() {
+    core_test_support::skip_if_no_network!();
+
+    let server = responses::start_mock_server().await;
+    let response_body = responses::sse(vec![
+        responses::ev_response_created("resp-1"),
+        responses::ev_completed("resp-1"),
+    ]);
+
+    let request_recorder = responses::mount_sse_once_match(
+        &server,
+        header(WEB_SEARCH_ELIGIBLE_HEADER, "true"),
+        response_body,
+    )
+    .await;
+
+    let test = test_codex().build(&server).await.expect("build test codex");
+    test.submit_turn("hello").await.expect("submit test prompt");
+
+    let request = request_recorder.single_request();
+    assert_eq!(
+        request.header(WEB_SEARCH_ELIGIBLE_HEADER).as_deref(),
+        Some("true")
+    );
+}
+
+#[tokio::test]
+async fn responses_stream_includes_web_search_eligible_header_false_when_disabled() {
+    core_test_support::skip_if_no_network!();
+
+    let server = responses::start_mock_server().await;
+    let response_body = responses::sse(vec![
+        responses::ev_response_created("resp-1"),
+        responses::ev_completed("resp-1"),
+    ]);
+
+    let request_recorder = responses::mount_sse_once_match(
+        &server,
+        header(WEB_SEARCH_ELIGIBLE_HEADER, "false"),
+        response_body,
+    )
+    .await;
+
+    let test = test_codex()
+        .with_config(|config| {
+            config.web_search_mode = Some(WebSearchMode::Disabled);
+        })
+        .build(&server)
+        .await
+        .expect("build test codex");
+    test.submit_turn("hello").await.expect("submit test prompt");
+
+    let request = request_recorder.single_request();
+    assert_eq!(
+        request.header(WEB_SEARCH_ELIGIBLE_HEADER).as_deref(),
+        Some("false")
+    );
+}
+
 #[tokio::test]
 async fn responses_respects_model_info_overrides_from_config() {
     core_test_support::skip_if_no_network!();
diff --git a/codex-rs/core/tests/suite/client.rs b/codex-rs/core/tests/suite/client.rs
index 18d3caf3bfc..6f659e1b649 100644
--- a/codex-rs/core/tests/suite/client.rs
+++ b/codex-rs/core/tests/suite/client.rs
@@ -14,6 +14,7 @@ use codex_core::ThreadManager;
 use codex_core::WireApi;
 use codex_core::auth::AuthCredentialsStoreMode;
 use codex_core::built_in_model_providers;
+use codex_core::default_client::originator;
 use codex_core::error::CodexErr;
 use codex_core::models_manager::manager::ModelsManager;
 use codex_core::protocol::EventMsg;
@@ -406,7 +407,7 @@ async fn includes_conversation_id_and_model_headers_in_request() {
     let request_originator = request.header("originator").expect("originator header");
 
     assert_eq!(request_session_id, session_id.to_string());
-    assert_eq!(request_originator, "codex_cli_rs");
+    assert_eq!(request_originator, originator().value);
     assert_eq!(request_authorization, "Bearer Test API Key");
 }
 
@@ -522,7 +523,7 @@ async fn chatgpt_auth_sends_correct_request() {
     let session_id = request.header("session_id").expect("session_id header");
     assert_eq!(session_id, thread_id.to_string());
 
-    assert_eq!(request_originator, "codex_cli_rs");
+    assert_eq!(request_originator, originator().value);
     assert_eq!(request_authorization, "Bearer Access Token");
     assert_eq!(request_chatgpt_account_id, "account_id");
     assert!(request_body["stream"].as_bool().unwrap());
diff --git a/codex-rs/core/tests/suite/model_tools.rs b/codex-rs/core/tests/suite/model_tools.rs
index 4eaf3735a37..8a4d0a77176 100644
--- a/codex-rs/core/tests/suite/model_tools.rs
+++ b/codex-rs/core/tests/suite/model_tools.rs
@@ -36,7 +36,7 @@ async fn collect_tool_identifiers_for_model(model: &str) -> Vec<String> {
     let mut builder = test_codex()
         .with_model(model)
         // Keep tool expectations stable when the default web_search mode changes.
-        .with_config(|config| config.web_search_mode = WebSearchMode::Cached);
+        .with_config(|config| config.web_search_mode = Some(WebSearchMode::Cached));
     let test = builder
         .build(&server)
         .await
diff --git a/codex-rs/core/tests/suite/prompt_caching.rs b/codex-rs/core/tests/suite/prompt_caching.rs
index b3ed78f69db..6ea5619bfe5 100644
--- a/codex-rs/core/tests/suite/prompt_caching.rs
+++ b/codex-rs/core/tests/suite/prompt_caching.rs
@@ -88,7 +88,7 @@ async fn prompt_tools_are_consistent_across_requests() -> anyhow::Result<()> {
             config.user_instructions = Some("be consistent and helpful".to_string());
             config.model = Some("gpt-5.1-codex-max".to_string());
             // Keep tool expectations stable when the default web_search mode changes.
-            config.web_search_mode = WebSearchMode::Cached;
+            config.web_search_mode = Some(WebSearchMode::Cached);
         })
         .build(&server)
         .await?;
diff --git a/codex-rs/core/tests/suite/web_search_cached.rs b/codex-rs/core/tests/suite/web_search_cached.rs
index 261efaf942b..1a69d8b7370 100644
--- a/codex-rs/core/tests/suite/web_search_cached.rs
+++ b/codex-rs/core/tests/suite/web_search_cached.rs
@@ -35,7 +35,7 @@ async fn web_search_mode_cached_sets_external_web_access_false_in_request_body()
     let mut builder = test_codex()
         .with_model("gpt-5-codex")
         .with_config(|config| {
-            config.web_search_mode = WebSearchMode::Cached;
+            config.web_search_mode = Some(WebSearchMode::Cached);
         });
     let test = builder
         .build(&server)
@@ -67,7 +67,7 @@ async fn web_search_mode_takes_precedence_over_legacy_flags_in_request_body() {
         .with_model("gpt-5-codex")
         .with_config(|config| {
             config.features.enable(Feature::WebSearchRequest);
-            config.web_search_mode = WebSearchMode::Cached;
+            config.web_search_mode = Some(WebSearchMode::Cached);
         });
     let test = builder
         .build(&server)