diff --git a/codex-rs/app-server/src/request_processors/thread_processor_tests.rs b/codex-rs/app-server/src/request_processors/thread_processor_tests.rs
index cc93600f2d..9d8fc7d75b 100644
--- a/codex-rs/app-server/src/request_processors/thread_processor_tests.rs
+++ b/codex-rs/app-server/src/request_processors/thread_processor_tests.rs
@@ -670,6 +670,7 @@ mod thread_processor_behavior_tests {
             websocket_connect_timeout_ms: None,
             requires_openai_auth: false,
             supports_websockets: true,
+            namespace_tools: None,
         };
         let config_manager = ConfigManager::new(
             temp_dir.path().to_path_buf(),
diff --git a/codex-rs/config/src/thread_config.rs b/codex-rs/config/src/thread_config.rs
index 273680d5ec..3bfe2a8b56 100644
--- a/codex-rs/config/src/thread_config.rs
+++ b/codex-rs/config/src/thread_config.rs
@@ -316,6 +316,7 @@ mod tests {
             websocket_connect_timeout_ms: None,
             requires_openai_auth: false,
             supports_websockets: true,
+            namespace_tools: None,
         }
     }
 }
diff --git a/codex-rs/config/src/thread_config/proto/codex.thread_config.v1.proto b/codex-rs/config/src/thread_config/proto/codex.thread_config.v1.proto
index 1efccfd1bf..1f57be5a7d 100644
--- a/codex-rs/config/src/thread_config/proto/codex.thread_config.v1.proto
+++ b/codex-rs/config/src/thread_config/proto/codex.thread_config.v1.proto
@@ -48,6 +48,7 @@ message ModelProvider {
   optional uint64 websocket_connect_timeout_ms = 15;
   bool requires_openai_auth = 16;
   bool supports_websockets = 17;
+  optional bool namespace_tools = 18;
 }
 
 message StringMap {
diff --git a/codex-rs/config/src/thread_config/proto/codex.thread_config.v1.rs b/codex-rs/config/src/thread_config/proto/codex.thread_config.v1.rs
index 30a76bc6b2..d8840ca39e 100644
--- a/codex-rs/config/src/thread_config/proto/codex.thread_config.v1.rs
+++ b/codex-rs/config/src/thread_config/proto/codex.thread_config.v1.rs
@@ -75,6 +75,8 @@ pub struct ModelProvider {
     pub requires_openai_auth: bool,
     #[prost(bool, tag = "17")]
     pub supports_websockets: bool,
+    #[prost(bool, optional, tag = "18")]
+    pub namespace_tools: ::core::option::Option<bool>,
 }
 #[derive(Clone, PartialEq, ::prost::Message)]
 pub struct StringMap {
diff --git a/codex-rs/config/src/thread_config/remote.rs b/codex-rs/config/src/thread_config/remote.rs
index 7a8e4ce88f..92fba4ca75 100644
--- a/codex-rs/config/src/thread_config/remote.rs
+++ b/codex-rs/config/src/thread_config/remote.rs
@@ -190,6 +190,7 @@ fn model_provider_from_proto(
         websocket_connect_timeout_ms: provider.websocket_connect_timeout_ms,
         requires_openai_auth: provider.requires_openai_auth,
         supports_websockets: provider.supports_websockets,
+        namespace_tools: provider.namespace_tools,
     };
     Ok((id, info))
 }
@@ -217,6 +218,7 @@ fn model_provider_to_proto(
         websocket_connect_timeout_ms,
         requires_openai_auth,
         supports_websockets,
+        namespace_tools,
     } = provider;
 
     proto::ModelProvider {
@@ -237,6 +239,7 @@ fn model_provider_to_proto(
         websocket_connect_timeout_ms,
         requires_openai_auth,
         supports_websockets,
+        namespace_tools,
     }
 }
 
@@ -473,6 +476,7 @@ mod tests {
                             websocket_connect_timeout_ms: Some(10_000),
                             requires_openai_auth: false,
                             supports_websockets: true,
+                            namespace_tools: Some(false),
                         }],
                         features: HashMap::from([
                             ("plugins".to_string(), false),
@@ -537,6 +541,7 @@ mod tests {
             requires_openai_auth: false,
             supports_websockets: true,
             aws: None,
+            namespace_tools: Some(false),
         }
     }
 
diff --git a/codex-rs/core/config.schema.json b/codex-rs/core/config.schema.json
index 31daf2feb4..da989aeab9 100644
--- a/codex-rs/core/config.schema.json
+++ b/codex-rs/core/config.schema.json
@@ -1531,6 +1531,11 @@
           "description": "Friendly display name.",
           "type": "string"
         },
+        "namespace_tools": {
+          "default": null,
+          "description": "Whether this provider understands Codex's `type: \"namespace\"` tool wrapper. When false, namespace tools are flattened to plain `<namespace>__<tool>` functions. When unset, provider-specific defaults apply: built-in OpenAI, Azure, and Amazon Bedrock providers keep namespaces while other configured providers flatten them.",
+          "type": "boolean"
+        },
         "query_params": {
           "additionalProperties": {
             "type": "string"
diff --git a/codex-rs/core/src/compact_tests.rs b/codex-rs/core/src/compact_tests.rs
index 550a7ec846..9c2b234875 100644
--- a/codex-rs/core/src/compact_tests.rs
+++ b/codex-rs/core/src/compact_tests.rs
@@ -235,6 +235,7 @@ fn should_use_remote_compact_task_for_azure_provider() {
         websocket_connect_timeout_ms: None,
         requires_openai_auth: false,
         supports_websockets: false,
+        namespace_tools: None,
     };
 
     assert!(should_use_remote_compact_task(&provider));
diff --git a/codex-rs/core/src/tools/handlers/mcp.rs b/codex-rs/core/src/tools/handlers/mcp.rs
index efb32aab94..cd346fa39d 100644
--- a/codex-rs/core/src/tools/handlers/mcp.rs
+++ b/codex-rs/core/src/tools/handlers/mcp.rs
@@ -4,6 +4,7 @@ use std::time::Instant;
 use crate::function_tool::FunctionCallError;
 use crate::mcp_tool_call::handle_mcp_tool_call;
 use crate::original_image_detail::can_request_original_image_detail;
+use crate::tools::canonical_flat_tool_name;
 use crate::tools::context::McpToolOutput;
 use crate::tools::context::ToolInvocation;
 use crate::tools::context::ToolPayload;
@@ -27,7 +28,6 @@ use serde_json::Map;
 use serde_json::Value;
 
 const LEGACY_MCP_TOOL_NAME_PREFIX: &str = "mcp__";
-const MCP_TOOL_NAME_DELIMITER: &str = "__";
 
 pub struct McpHandler {
     tool_info: ToolInfo,
@@ -41,18 +41,9 @@ impl McpHandler {
     }
 
     fn hook_tool_name(&self) -> HookToolName {
-        HookToolName::new(ensure_mcp_prefix(&join_tool_name(&self.tool_name())))
-    }
-}
-
-fn join_tool_name(tool_name: &ToolName) -> String {
-    match tool_name.namespace.as_deref() {
-        Some(namespace) => {
-            let namespace = namespace.trim_end_matches('_');
-            let name = tool_name.name.trim_start_matches('_');
-            format!("{namespace}{MCP_TOOL_NAME_DELIMITER}{name}")
-        }
-        None => tool_name.name.clone(),
+        let tool_name = self.tool_name();
+        let canonical = canonical_flat_tool_name(&tool_name);
+        HookToolName::new(ensure_mcp_prefix(&canonical))
     }
 }
 
diff --git a/codex-rs/core/src/tools/mod.rs b/codex-rs/core/src/tools/mod.rs
index cd10d246db..60edc1968a 100644
--- a/codex-rs/core/src/tools/mod.rs
+++ b/codex-rs/core/src/tools/mod.rs
@@ -45,6 +45,25 @@ pub(crate) fn flat_tool_name(tool_name: &ToolName) -> Cow<'_, str> {
     }
 }
 
+const NAMESPACED_TOOL_NAME_DELIMITER: &str = "__";
+
+/// Joins a namespace and tool name into the canonical `<namespace>__<tool>` form,
+/// trimming stray underscores so the `__` delimiter is never doubled.
+pub(in crate::tools) fn join_namespaced_tool_name(namespace: &str, name: &str) -> String {
+    let namespace = namespace.trim_end_matches('_');
+    let name = name.trim_start_matches('_');
+    format!("{namespace}{NAMESPACED_TOOL_NAME_DELIMITER}{name}")
+}
+
+/// Canonical flat name with the `__` delimiter, matching what hooks emit and
+/// proxies expect. Unlike `flat_tool_name`, namespace and tool are not joined raw.
+pub(in crate::tools) fn canonical_flat_tool_name(tool_name: &ToolName) -> Cow<'_, str> {
+    match tool_name.namespace.as_deref() {
+        Some(namespace) => Cow::Owned(join_namespaced_tool_name(namespace, &tool_name.name)),
+        None => Cow::Borrowed(tool_name.name.as_str()),
+    }
+}
+
 pub(crate) fn tool_user_shell_type(
     user_shell: &crate::shell::Shell,
 ) -> codex_tools::ToolUserShellType {
diff --git a/codex-rs/core/src/tools/registry.rs b/codex-rs/core/src/tools/registry.rs
index 76e3f5f341..f418d6a8d2 100644
--- a/codex-rs/core/src/tools/registry.rs
+++ b/codex-rs/core/src/tools/registry.rs
@@ -13,6 +13,7 @@ use crate::memory_usage::emit_metric_for_tool_read;
 use crate::sandbox_tags::permission_profile_policy_tag;
 use crate::sandbox_tags::permission_profile_sandbox_tag;
 use crate::session::turn_context::TurnContext;
+use crate::tools::canonical_flat_tool_name;
 use crate::tools::context::FunctionToolOutput;
 use crate::tools::context::ToolInvocation;
 use crate::tools::context::ToolOutput;
@@ -355,7 +356,17 @@ impl ToolRegistry {
     }
 
     fn tool(&self, name: &ToolName) -> Option<Arc<dyn CoreToolRuntime>> {
-        self.tools.get(name).map(Arc::clone)
+        if let Some(tool) = self.tools.get(name) {
+            return Some(Arc::clone(tool));
+        }
+        // Fall back to matching by canonical flattened name so a flat
+        // `<namespace>__<tool>` call (emitted for providers without namespace
+        // support, or flattened by a proxy) resolves to its namespaced runtime.
+        let canonical = canonical_flat_tool_name(name);
+        self.tools
+            .iter()
+            .find(|(key, _)| canonical_flat_tool_name(key) == canonical)
+            .map(|(_, tool)| Arc::clone(tool))
     }
 
     #[cfg(test)]
diff --git a/codex-rs/core/src/tools/registry_tests.rs b/codex-rs/core/src/tools/registry_tests.rs
index 67613f1d08..a9b36fb0be 100644
--- a/codex-rs/core/src/tools/registry_tests.rs
+++ b/codex-rs/core/src/tools/registry_tests.rs
@@ -178,6 +178,32 @@ fn handler_looks_up_namespaced_aliases_explicitly() {
     );
 }
 
+#[test]
+fn handler_resolves_flat_name_to_namespaced_runtime() {
+    // Runtime namespace shape: `mcp__mini` with no trailing `__`.
+    let namespaced_name = codex_tools::ToolName::namespaced("mcp__mini", "record_note");
+    let handler = Arc::new(TestHandler {
+        tool_name: namespaced_name.clone(),
+    }) as Arc<dyn CoreToolRuntime>;
+    let registry = ToolRegistry::new(HashMap::from([(
+        namespaced_name.clone(),
+        Arc::clone(&handler),
+    )]));
+
+    // The canonical flat name (what flattening emits, and what a proxy produces)
+    // resolves to the namespaced runtime.
+    let canonical = registry.tool(&codex_tools::ToolName::plain("mcp__mini__record_note"));
+    assert!(canonical.as_ref().is_some_and(|h| Arc::ptr_eq(h, &handler)));
+
+    // Exact namespaced lookup still works, and unrelated names do not resolve.
+    assert!(registry.tool(&namespaced_name).is_some());
+    assert!(
+        registry
+            .tool(&codex_tools::ToolName::plain("mcp__other__record_note"))
+            .is_none()
+    );
+}
+
 #[tokio::test]
 async fn function_tools_expose_default_hook_payloads_and_rewrites() -> anyhow::Result<()> {
     let (session, turn) = crate::session::tests::make_session_and_context().await;
diff --git a/codex-rs/core/src/tools/spec_plan.rs b/codex-rs/core/src/tools/spec_plan.rs
index 76c1e4389c..4492c95ff5 100644
--- a/codex-rs/core/src/tools/spec_plan.rs
+++ b/codex-rs/core/src/tools/spec_plan.rs
@@ -49,6 +49,7 @@ use crate::tools::handlers::view_image_spec::ViewImageToolOptions;
 use crate::tools::hosted_spec::WebSearchToolOptions;
 use crate::tools::hosted_spec::create_image_generation_tool;
 use crate::tools::hosted_spec::create_web_search_tool;
+use crate::tools::join_namespaced_tool_name;
 use crate::tools::registry::CoreToolRuntime;
 use crate::tools::registry::ToolExposure;
 use crate::tools::registry::ToolRegistry;
@@ -221,16 +222,39 @@ fn build_model_visible_specs_and_registry(
     specs.extend(hosted_specs);
 
     let registry = ToolRegistry::from_tools(runtimes);
-    let model_visible_specs = merge_into_namespaces(specs)
-        .into_iter()
-        .filter(|spec| {
-            namespace_tools_enabled(turn_context) || !matches!(spec, ToolSpec::Namespace(_))
-        })
-        .collect();
+    let merged_specs = merge_into_namespaces(specs);
+    // Providers that do not understand the `type: "namespace"` wrapper get the
+    // namespaced tools flattened into plain functions rather than dropped.
+    let model_visible_specs = if namespace_tools_enabled(turn_context) {
+        merged_specs
+    } else {
+        merged_specs
+            .into_iter()
+            .flat_map(|spec| match spec {
+                ToolSpec::Namespace(namespace) => flatten_namespace_spec(namespace),
+                other => vec![other],
+            })
+            .collect()
+    };
 
     (model_visible_specs, registry)
 }
 
+/// Flattens a namespace into plain `function` specs named `<namespace>__<tool>`.
+/// The canonical names match hooks and proxies, so the registry resolves them.
+fn flatten_namespace_spec(namespace: ResponsesApiNamespace) -> Vec<ToolSpec> {
+    namespace
+        .tools
+        .into_iter()
+        .map(|tool| match tool {
+            ResponsesApiNamespaceTool::Function(mut function) => {
+                function.name = join_namespaced_tool_name(&namespace.name, &function.name);
+                ToolSpec::Function(function)
+            }
+        })
+        .collect()
+}
+
 fn spec_for_model_request(
     turn_context: &TurnContext,
     exposure: ToolExposure,
diff --git a/codex-rs/core/src/tools/spec_plan_tests.rs b/codex-rs/core/src/tools/spec_plan_tests.rs
index 7a1e5d8aa9..02bbcce05a 100644
--- a/codex-rs/core/src/tools/spec_plan_tests.rs
+++ b/codex-rs/core/src/tools/spec_plan_tests.rs
@@ -264,6 +264,15 @@ fn set_web_search_mode(turn: &mut TurnContext, mode: WebSearchMode) {
     });
 }
 
+fn disable_namespace_tools(turn: &mut TurnContext) {
+    let mut provider_info = turn.config.model_provider.clone();
+    provider_info.namespace_tools = Some(false);
+    update_config(turn, |config| {
+        config.model_provider = provider_info.clone();
+    });
+    turn.provider = create_model_provider(provider_info, turn.auth_manager.clone());
+}
+
 fn use_chatgpt_auth(turn: &mut TurnContext) {
     turn.auth_manager = Some(AuthManager::from_auth_for_testing(
         CodexAuth::create_dummy_chatgpt_auth_for_testing(),
@@ -735,6 +744,34 @@ async fn mcp_and_tool_search_follow_direct_and_deferred_tool_exposure() {
     ]);
 }
 
+#[tokio::test]
+async fn namespace_tools_disabled_flattens_mcp_namespace_into_function() {
+    // Use the runtime namespace shape (`mcp__mini`, no trailing `__`).
+    let probe = probe_with(
+        disable_namespace_tools,
+        ToolPlanInputs {
+            mcp_tools: Some(vec![mcp_tool("mini", "mcp__mini", "record_note")]),
+            ..ToolPlanInputs::default()
+        },
+    )
+    .await;
+
+    // The MCP tool is exposed as a flat function with the canonical `__`
+    // delimiter, not a namespace wrapper and not a delimiter-less concatenation.
+    probe.assert_visible_contains(&["mcp__mini__record_note"]);
+    probe.assert_visible_lacks(&["mcp__minirecord_note"]);
+    assert!(probe.namespace_function_names("mcp__mini").is_empty());
+    assert!(matches!(
+        probe.visible_spec("mcp__mini__record_note"),
+        ToolSpec::Function(_)
+    ));
+
+    // The runtime is still registered under its namespaced identity.
+    probe.assert_registered_contains(&[
+        &ToolName::namespaced("mcp__mini", "record_note").to_string()
+    ]);
+}
+
 #[tokio::test]
 async fn deferred_extension_tools_are_discoverable_with_tool_search() {
     let plan = probe_with(
diff --git a/codex-rs/core/tests/responses_headers.rs b/codex-rs/core/tests/responses_headers.rs
index cda5ffcdb0..b9cb1d2152 100644
--- a/codex-rs/core/tests/responses_headers.rs
+++ b/codex-rs/core/tests/responses_headers.rs
@@ -87,6 +87,7 @@ async fn responses_stream_includes_subagent_header_on_review() {
         websocket_connect_timeout_ms: None,
         requires_openai_auth: false,
         supports_websockets: false,
+        namespace_tools: None,
     };
 
     let codex_home = TempDir::new().expect("failed to create TempDir");
@@ -217,6 +218,7 @@ async fn responses_stream_includes_subagent_header_on_other() {
         websocket_connect_timeout_ms: None,
         requires_openai_auth: false,
         supports_websockets: false,
+        namespace_tools: None,
     };
 
     let codex_home = TempDir::new().expect("failed to create TempDir");
@@ -328,6 +330,7 @@ async fn responses_respects_model_info_overrides_from_config() {
         websocket_connect_timeout_ms: None,
         requires_openai_auth: false,
         supports_websockets: false,
+        namespace_tools: None,
     };
 
     let codex_home = TempDir::new().expect("failed to create TempDir");
diff --git a/codex-rs/core/tests/suite/client.rs b/codex-rs/core/tests/suite/client.rs
index c41593f516..0cf46abae9 100644
--- a/codex-rs/core/tests/suite/client.rs
+++ b/codex-rs/core/tests/suite/client.rs
@@ -927,6 +927,7 @@ async fn send_provider_auth_request(server: &MockServer, auth: ModelProviderAuth
         websocket_connect_timeout_ms: None,
         requires_openai_auth: false,
         supports_websockets: false,
+        namespace_tools: None,
     };
 
     let codex_home = TempDir::new().unwrap();
@@ -2421,6 +2422,7 @@ async fn azure_responses_request_includes_store_and_reasoning_ids() {
         websocket_connect_timeout_ms: None,
         requires_openai_auth: false,
         supports_websockets: false,
+        namespace_tools: None,
     };
 
     let codex_home = TempDir::new().unwrap();
@@ -3028,6 +3030,7 @@ async fn azure_overrides_assign_properties_used_for_responses_url() {
         websocket_connect_timeout_ms: None,
         requires_openai_auth: false,
         supports_websockets: false,
+        namespace_tools: None,
     };
 
     // Init session
@@ -3117,6 +3120,7 @@ async fn env_var_overrides_loaded_auth() {
         websocket_connect_timeout_ms: None,
         requires_openai_auth: false,
         supports_websockets: false,
+        namespace_tools: None,
     };
 
     // Init session
diff --git a/codex-rs/core/tests/suite/client_websockets.rs b/codex-rs/core/tests/suite/client_websockets.rs
index 4aac3dcbd8..c19e0f62b8 100755
--- a/codex-rs/core/tests/suite/client_websockets.rs
+++ b/codex-rs/core/tests/suite/client_websockets.rs
@@ -2109,6 +2109,7 @@ fn websocket_provider_with_connect_timeout(
         websocket_connect_timeout_ms,
         requires_openai_auth: false,
         supports_websockets: true,
+        namespace_tools: None,
     }
 }
 
diff --git a/codex-rs/core/tests/suite/rmcp_client.rs b/codex-rs/core/tests/suite/rmcp_client.rs
index 961c66079a..f841f1788d 100644
--- a/codex-rs/core/tests/suite/rmcp_client.rs
+++ b/codex-rs/core/tests/suite/rmcp_client.rs
@@ -830,6 +830,96 @@ async fn stdio_mcp_tool_call_includes_sandbox_state_meta() -> anyhow::Result<()>
     Ok(())
 }
 
+#[tokio::test(flavor = "multi_thread", worker_threads = 1)]
+async fn stdio_mcp_tool_call_flattens_namespace_when_provider_disables_it() -> anyhow::Result<()> {
+    skip_if_no_network!(Ok(()));
+
+    let server = responses::start_mock_server().await;
+
+    let call_id = "flat-mcp-call";
+    let server_name = "rmcp";
+    let flat_tool_name = format!("mcp__{server_name}__echo");
+    let call_mock = mount_sse_once(
+        &server,
+        responses::sse(vec![
+            responses::ev_response_created("resp-1"),
+            responses::ev_function_call(call_id, &flat_tool_name, r#"{"message":"ping"}"#),
+            responses::ev_completed("resp-1"),
+        ]),
+    )
+    .await;
+    let final_mock = mount_sse_once(
+        &server,
+        responses::sse(vec![
+            responses::ev_assistant_message("msg-1", "rmcp flat tool completed successfully."),
+            responses::ev_completed("resp-2"),
+        ]),
+    )
+    .await;
+
+    let rmcp_test_server_bin = remote_aware_stdio_server_bin()?;
+    let fixture = test_codex()
+        .with_config(move |config| {
+            config.model_provider.namespace_tools = Some(false);
+            insert_mcp_server(
+                config,
+                server_name,
+                stdio_transport(rmcp_test_server_bin, /*env*/ None, Vec::new()),
+                TestMcpServerOptions {
+                    environment_id: remote_aware_environment_id(),
+                    ..Default::default()
+                },
+            );
+        })
+        .build_with_remote_env(&server)
+        .await?;
+
+    wait_for_mcp_server(&fixture.codex, server_name).await?;
+
+    fixture
+        .submit_turn_with_permission_profile(
+            "call the flat rmcp echo tool",
+            PermissionProfile::read_only(),
+        )
+        .await?;
+
+    let request = call_mock.single_request();
+    let request_body = request.body_json();
+    let tools = request_body
+        .get("tools")
+        .and_then(Value::as_array)
+        .expect("Responses request should include tools");
+    assert!(
+        tools.iter().any(|tool| {
+            tool.get("type").and_then(Value::as_str) == Some("function")
+                && tool.get("name").and_then(Value::as_str) == Some(flat_tool_name.as_str())
+        }),
+        "MCP tool should be sent as a flat function: {:?}",
+        request_body
+    );
+    assert!(
+        tools.iter().all(|tool| {
+            tool.get("type").and_then(Value::as_str) != Some("namespace")
+                || tool.get("name").and_then(Value::as_str) != Some("mcp__rmcp")
+        }),
+        "MCP namespace wrapper should be omitted: {:?}",
+        request_body
+    );
+
+    let output = final_mock
+        .single_request()
+        .function_call_output_text(call_id)
+        .expect("function_call_output should be present for flat MCP call");
+    assert!(
+        output.contains("ECHOING: ping"),
+        "flat MCP call should execute against the namespaced runtime: {output}"
+    );
+
+    server.verify().await;
+
+    Ok(())
+}
+
 #[tokio::test(flavor = "multi_thread", worker_threads = 2)]
 async fn stdio_mcp_parallel_tool_calls_default_false_runs_serially() -> anyhow::Result<()> {
     skip_if_no_network!(Ok(()));
diff --git a/codex-rs/core/tests/suite/stream_error_allows_next_turn.rs b/codex-rs/core/tests/suite/stream_error_allows_next_turn.rs
index 1870feab9f..5a6de14580 100644
--- a/codex-rs/core/tests/suite/stream_error_allows_next_turn.rs
+++ b/codex-rs/core/tests/suite/stream_error_allows_next_turn.rs
@@ -81,6 +81,7 @@ async fn continue_after_stream_error() {
         websocket_connect_timeout_ms: None,
         requires_openai_auth: false,
         supports_websockets: false,
+        namespace_tools: None,
     };
 
     let TestCodex { codex, .. } = test_codex()
diff --git a/codex-rs/core/tests/suite/stream_no_completed.rs b/codex-rs/core/tests/suite/stream_no_completed.rs
index 6e028279b1..d2251afde0 100644
--- a/codex-rs/core/tests/suite/stream_no_completed.rs
+++ b/codex-rs/core/tests/suite/stream_no_completed.rs
@@ -64,6 +64,7 @@ async fn retries_on_early_close() {
         websocket_connect_timeout_ms: None,
         requires_openai_auth: false,
         supports_websockets: false,
+        namespace_tools: None,
     };
 
     let TestCodex { codex, .. } = test_codex()
diff --git a/codex-rs/login/src/auth_env_telemetry.rs b/codex-rs/login/src/auth_env_telemetry.rs
index 3cec5a4ce3..5f6d9ae642 100644
--- a/codex-rs/login/src/auth_env_telemetry.rs
+++ b/codex-rs/login/src/auth_env_telemetry.rs
@@ -76,6 +76,7 @@ mod tests {
             websocket_connect_timeout_ms: None,
             requires_openai_auth: false,
             supports_websockets: false,
+            namespace_tools: None,
         };
 
         let telemetry =
diff --git a/codex-rs/model-provider-info/src/lib.rs b/codex-rs/model-provider-info/src/lib.rs
index 5f0f840508..c7084832d8 100644
--- a/codex-rs/model-provider-info/src/lib.rs
+++ b/codex-rs/model-provider-info/src/lib.rs
@@ -134,6 +134,13 @@ pub struct ModelProviderInfo {
     /// Whether this provider supports the Responses API WebSocket transport.
     #[serde(default)]
     pub supports_websockets: bool,
+    /// Whether this provider understands Codex's `type: "namespace"` tool wrapper.
+    /// When false, namespace tools are flattened to plain `<namespace>__<tool>`
+    /// functions. When unset, provider-specific defaults apply: built-in
+    /// OpenAI, Azure, and Amazon Bedrock providers keep namespaces while other
+    /// configured providers flatten them.
+    #[serde(default)]
+    pub namespace_tools: Option<bool>,
 }
 
 /// AWS SigV4 auth configuration for a model provider.
@@ -355,6 +362,7 @@ impl ModelProviderInfo {
             websocket_connect_timeout_ms: None,
             requires_openai_auth: true,
             supports_websockets: true,
+            namespace_tools: None,
         }
     }
 
@@ -385,6 +393,7 @@ impl ModelProviderInfo {
             websocket_connect_timeout_ms: None,
             requires_openai_auth: false,
             supports_websockets: false,
+            namespace_tools: None,
         }
     }
 
@@ -516,6 +525,7 @@ pub fn create_oss_provider_with_base_url(base_url: &str, wire_api: WireApi) -> M
         websocket_connect_timeout_ms: None,
         requires_openai_auth: false,
         supports_websockets: false,
+        namespace_tools: None,
     }
 }
 
diff --git a/codex-rs/model-provider-info/src/model_provider_info_tests.rs b/codex-rs/model-provider-info/src/model_provider_info_tests.rs
index a303050dc1..8a5dbf4b6c 100644
--- a/codex-rs/model-provider-info/src/model_provider_info_tests.rs
+++ b/codex-rs/model-provider-info/src/model_provider_info_tests.rs
@@ -29,6 +29,7 @@ base_url = "http://localhost:11434/v1"
         websocket_connect_timeout_ms: None,
         requires_openai_auth: false,
         supports_websockets: false,
+        namespace_tools: None,
     };
 
     let provider: ModelProviderInfo = toml::from_str(azure_provider_toml).unwrap();
@@ -63,6 +64,7 @@ query_params = { api-version = "2025-04-01-preview" }
         websocket_connect_timeout_ms: None,
         requires_openai_auth: false,
         supports_websockets: false,
+        namespace_tools: None,
     };
 
     let provider: ModelProviderInfo = toml::from_str(azure_provider_toml).unwrap();
@@ -77,6 +79,7 @@ base_url = "https://example.com"
 env_key = "API_KEY"
 http_headers = { "X-Example-Header" = "example-value" }
 env_http_headers = { "X-Example-Env-Header" = "EXAMPLE_ENV_VAR" }
+namespace_tools = false
         "#;
     let expected_provider = ModelProviderInfo {
         name: "Example".into(),
@@ -100,6 +103,7 @@ env_http_headers = { "X-Example-Env-Header" = "EXAMPLE_ENV_VAR" }
         websocket_connect_timeout_ms: None,
         requires_openai_auth: false,
         supports_websockets: false,
+        namespace_tools: Some(false),
     };
 
     let provider: ModelProviderInfo = toml::from_str(azure_provider_toml).unwrap();
@@ -168,6 +172,7 @@ fn test_supports_remote_compaction_for_azure_name() {
         websocket_connect_timeout_ms: None,
         requires_openai_auth: false,
         supports_websockets: false,
+        namespace_tools: None,
     };
 
     assert!(provider.supports_remote_compaction());
@@ -193,6 +198,7 @@ fn test_supports_remote_compaction_for_non_openai_non_azure_provider() {
         websocket_connect_timeout_ms: None,
         requires_openai_auth: false,
         supports_websockets: false,
+        namespace_tools: None,
     };
 
     assert!(!provider.supports_remote_compaction());
@@ -276,6 +282,7 @@ fn test_create_amazon_bedrock_provider() {
             websocket_connect_timeout_ms: None,
             requires_openai_auth: false,
             supports_websockets: false,
+            namespace_tools: None,
         }
     );
 }
diff --git a/codex-rs/model-provider/src/amazon_bedrock/mod.rs b/codex-rs/model-provider/src/amazon_bedrock/mod.rs
index d44e7cbd02..5a1f4cae4a 100644
--- a/codex-rs/model-provider/src/amazon_bedrock/mod.rs
+++ b/codex-rs/model-provider/src/amazon_bedrock/mod.rs
@@ -101,8 +101,11 @@ impl ModelProvider for AmazonBedrockModelProvider {
     }
 
     fn capabilities(&self) -> ProviderCapabilities {
+        // Bedrock hosts OpenAI models that expand the namespace wrapper, so it
+        // defaults on. Mantle endpoints that reject the wrapper can opt out with
+        // an explicit `namespace_tools = false`.
         ProviderCapabilities {
-            namespace_tools: true,
+            namespace_tools: self.info.namespace_tools.unwrap_or(true),
             image_generation: false,
             web_search: false,
         }
@@ -257,6 +260,15 @@ mod tests {
         );
     }
 
+    #[test]
+    fn capabilities_namespace_tools_honors_explicit_opt_out() {
+        let mut info = ModelProviderInfo::create_amazon_bedrock_provider(/*aws*/ None);
+        info.namespace_tools = Some(false);
+        let provider = AmazonBedrockModelProvider::new(info, /*auth_manager*/ None);
+
+        assert!(!provider.capabilities().namespace_tools);
+    }
+
     #[test]
     fn approval_review_preferred_model_uses_bedrock_gpt_5_4() {
         let provider = AmazonBedrockModelProvider::new(
diff --git a/codex-rs/model-provider/src/provider.rs b/codex-rs/model-provider/src/provider.rs
index f794d49f42..0f9a9e3fc1 100644
--- a/codex-rs/model-provider/src/provider.rs
+++ b/codex-rs/model-provider/src/provider.rs
@@ -6,6 +6,7 @@ use std::sync::Arc;
 
 use codex_api::Provider;
 use codex_api::SharedAuthProvider;
+use codex_api::is_azure_responses_provider;
 use codex_login::AuthManager;
 use codex_login::CodexAuth;
 use codex_model_provider_info::ModelProviderInfo;
@@ -42,6 +43,15 @@ impl Default for ProviderCapabilities {
     }
 }
 
+/// Whether a provider advertises the `type: "namespace"` tool wrapper: an
+/// explicit `namespace_tools` if set, otherwise providers known to support it.
+fn resolve_namespace_tools(info: &ModelProviderInfo) -> bool {
+    info.namespace_tools.unwrap_or_else(|| {
+        info.requires_openai_auth
+            || is_azure_responses_provider(&info.name, info.base_url.as_deref())
+    })
+}
+
 /// Current app-visible account state for a model provider.
 #[derive(Debug, Clone, PartialEq, Eq)]
 pub struct ProviderAccountState {
@@ -218,6 +228,13 @@ impl ModelProvider for ConfiguredModelProvider {
         &self.info
     }
 
+    fn capabilities(&self) -> ProviderCapabilities {
+        ProviderCapabilities {
+            namespace_tools: resolve_namespace_tools(&self.info),
+            ..ProviderCapabilities::default()
+        }
+    }
+
     fn auth_manager(&self) -> Option<Arc<AuthManager>> {
         self.auth_manager.clone()
     }
@@ -367,6 +384,7 @@ mod tests {
             websocket_connect_timeout_ms: None,
             requires_openai_auth: false,
             supports_websockets: false,
+            namespace_tools: None,
         }
     }
 
@@ -414,6 +432,38 @@ mod tests {
         assert_eq!(provider.capabilities(), ProviderCapabilities::default());
     }
 
+    #[test]
+    fn configured_non_openai_provider_flattens_namespace_tools() {
+        let provider = create_model_provider(
+            provider_for("https://example.test/v1".to_string()),
+            /*auth_manager*/ None,
+        );
+
+        assert!(!provider.capabilities().namespace_tools);
+    }
+
+    #[test]
+    fn configured_azure_provider_keeps_namespace_tools() {
+        let mut azure = provider_for("https://xxxxx.openai.azure.com/openai".to_string());
+        azure.name = "azure".to_string();
+        let provider = create_model_provider(azure, /*auth_manager*/ None);
+
+        assert!(provider.capabilities().namespace_tools);
+    }
+
+    #[test]
+    fn configured_provider_namespace_tools_honors_explicit_override() {
+        let mut non_openai = provider_for("https://example.test/v1".to_string());
+        non_openai.namespace_tools = Some(true);
+        let provider = create_model_provider(non_openai, /*auth_manager*/ None);
+        assert!(provider.capabilities().namespace_tools);
+
+        let mut openai = ModelProviderInfo::create_openai_provider(/*base_url*/ None);
+        openai.namespace_tools = Some(false);
+        let provider = create_model_provider(openai, /*auth_manager*/ None);
+        assert!(!provider.capabilities().namespace_tools);
+    }
+
     #[test]
     fn configured_provider_uses_default_approval_review_preferred_model() {
         let provider = create_model_provider(