fix: retire Feature.RmcpClient

codex-rs/cli/src/mcp_cmd.rs

@@ -14,7 +14,6 @@ use codex_core::config::find_codex_home;
 use codex_core::config::load_global_mcp_servers;
 use codex_core::config::types::McpServerConfig;
 use codex_core::config::types::McpServerTransportConfig;
-use codex_core::features::Feature;
 use codex_core::mcp::auth::compute_auth_statuses;
 use codex_core::protocol::McpAuthStatus;
 use codex_rmcp_client::delete_oauth_tokens;
@@ -53,11 +52,9 @@ pub enum McpSubcommand {
     Remove(RemoveArgs),
 
     /// [experimental] Authenticate with a configured MCP server via OAuth.
-    /// Requires experimental_use_rmcp_client = true in config.toml.
     Login(LoginArgs),
 
     /// [experimental] Remove stored OAuth credentials for a server.
-    /// Requires experimental_use_rmcp_client = true in config.toml.
     Logout(LogoutArgs),
 }
 
@@ -283,24 +280,17 @@ async fn run_add(config_overrides: &CliConfigOverrides, add_args: AddArgs) -> Re
     {
         match supports_oauth_login(&url).await {
             Ok(true) => {
-                if !config.features.enabled(Feature::RmcpClient) {
-                    println!(
-                        "MCP server supports login. Add `experimental_use_rmcp_client = true` \
-                         to your config.toml and run `codex mcp login {name}` to login."
-                    );
-                } else {
-                    println!("Detected OAuth support. Starting OAuth flow…");
-                    perform_oauth_login(
-                        &name,
-                        &url,
-                        config.mcp_oauth_credentials_store_mode,
-                        http_headers.clone(),
-                        env_http_headers.clone(),
-                        &Vec::new(),
-                    )
-                    .await?;
-                    println!("Successfully logged in.");
-                }
+                println!("Detected OAuth support. Starting OAuth flow…");
+                perform_oauth_login(
+                    &name,
+                    &url,
+                    config.mcp_oauth_credentials_store_mode,
+                    http_headers.clone(),
+                    env_http_headers.clone(),
+                    &Vec::new(),
+                )
+                .await?;
+                println!("Successfully logged in.");
             }
             Ok(false) => {}
             Err(_) => println!(
@@ -353,12 +343,6 @@ async fn run_login(config_overrides: &CliConfigOverrides, login_args: LoginArgs)
         .await
         .context("failed to load configuration")?;
 
-    if !config.features.enabled(Feature::RmcpClient) {
-        bail!(
-            "OAuth login is only supported when [features].rmcp_client is true in config.toml. See https://github.com/openai/codex/blob/main/docs/config.md#feature-flags for details."
-        );
-    }
-
     let LoginArgs { name, scopes } = login_args;
 
     let Some(server) = config.mcp_servers.get(&name) else {

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

@@ -251,10 +251,6 @@ pub struct Config {
     /// If set to `true`, used only the experimental unified exec tool.
     pub use_experimental_unified_exec_tool: bool,
 
-    /// If set to `true`, use the experimental official Rust MCP client.
-    /// https://github.com/modelcontextprotocol/rust-sdk
-    pub use_experimental_use_rmcp_client: bool,
-
     /// Centralized feature flags; source of truth for feature gating.
     pub features: Features,
 
@@ -718,7 +714,6 @@ pub struct ConfigToml {
     pub experimental_instructions_file: Option<PathBuf>,
     pub experimental_compact_prompt_file: Option<PathBuf>,
     pub experimental_use_unified_exec_tool: Option<bool>,
-    pub experimental_use_rmcp_client: Option<bool>,
     pub experimental_use_freeform_apply_patch: Option<bool>,
     pub experimental_sandbox_command_assessment: Option<bool>,
     /// Preferred OSS provider for local models, e.g. "lmstudio" or "ollama".
@@ -1088,7 +1083,6 @@ impl Config {
         let include_apply_patch_tool_flag = features.enabled(Feature::ApplyPatchFreeform);
         let tools_web_search_request = features.enabled(Feature::WebSearchRequest);
         let use_experimental_unified_exec_tool = features.enabled(Feature::UnifiedExec);
-        let use_experimental_use_rmcp_client = features.enabled(Feature::RmcpClient);
         let experimental_sandbox_command_assessment =
             features.enabled(Feature::SandboxCommandAssessment);
 
@@ -1241,7 +1235,6 @@ impl Config {
             tools_web_search_request,
             experimental_sandbox_command_assessment,
             use_experimental_unified_exec_tool,
-            use_experimental_use_rmcp_client,
             features,
             active_profile: active_profile_name,
             active_project,
@@ -1809,7 +1802,6 @@ trust_level = "trusted"
         let codex_home = TempDir::new()?;
         let cfg = ConfigToml {
             experimental_use_unified_exec_tool: Some(true),
-            experimental_use_rmcp_client: Some(true),
             experimental_use_freeform_apply_patch: Some(true),
             ..Default::default()
         };
@@ -1822,12 +1814,10 @@ trust_level = "trusted"
 
         assert!(config.features.enabled(Feature::ApplyPatchFreeform));
         assert!(config.features.enabled(Feature::UnifiedExec));
-        assert!(config.features.enabled(Feature::RmcpClient));
 
         assert!(config.include_apply_patch_tool);
 
         assert!(config.use_experimental_unified_exec_tool);
-        assert!(config.use_experimental_use_rmcp_client);
 
         Ok(())
     }
@@ -2994,7 +2984,6 @@ model_verbosity = "high"
                 tools_web_search_request: false,
                 experimental_sandbox_command_assessment: false,
                 use_experimental_unified_exec_tool: false,
-                use_experimental_use_rmcp_client: false,
                 features: Features::with_defaults(),
                 active_profile: Some("o3".to_string()),
                 active_project: ProjectConfig { trust_level: None },
@@ -3068,7 +3057,6 @@ model_verbosity = "high"
             tools_web_search_request: false,
             experimental_sandbox_command_assessment: false,
             use_experimental_unified_exec_tool: false,
-            use_experimental_use_rmcp_client: false,
             features: Features::with_defaults(),
             active_profile: Some("gpt3".to_string()),
             active_project: ProjectConfig { trust_level: None },
@@ -3157,7 +3145,6 @@ model_verbosity = "high"
             tools_web_search_request: false,
             experimental_sandbox_command_assessment: false,
             use_experimental_unified_exec_tool: false,
-            use_experimental_use_rmcp_client: false,
             features: Features::with_defaults(),
             active_profile: Some("zdr".to_string()),
             active_project: ProjectConfig { trust_level: None },
@@ -3232,7 +3219,6 @@ model_verbosity = "high"
             tools_web_search_request: false,
             experimental_sandbox_command_assessment: false,
             use_experimental_unified_exec_tool: false,
-            use_experimental_use_rmcp_client: false,
             features: Features::with_defaults(),
             active_profile: Some("gpt5".to_string()),
             active_project: ProjectConfig { trust_level: None },

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

@@ -25,7 +25,6 @@ pub struct ConfigProfile {
     pub experimental_compact_prompt_file: Option<PathBuf>,
     pub include_apply_patch_tool: Option<bool>,
     pub experimental_use_unified_exec_tool: Option<bool>,
-    pub experimental_use_rmcp_client: Option<bool>,
     pub experimental_use_freeform_apply_patch: Option<bool>,
     pub experimental_sandbox_command_assessment: Option<bool>,
     pub tools_web_search: Option<bool>,

codex-rs/core/src/features.rs

@@ -125,7 +125,7 @@ impl Features {
     }
 
     pub fn enabled(&self, f: Feature) -> bool {
-        self.enabled.contains(&f)
+        f == Feature::RmcpClient || self.enabled.contains(&f)
     }
 
     pub fn enable(&mut self, f: Feature) -> &mut Self {
@@ -134,7 +134,9 @@ impl Features {
     }
 
     pub fn disable(&mut self, f: Feature) -> &mut Self {
-        self.enabled.remove(&f);
+        if f != Feature::RmcpClient {
+            self.enabled.remove(&f);
+        }
         self
     }
 
@@ -162,6 +164,18 @@ impl Features {
     pub fn apply_map(&mut self, m: &BTreeMap<String, bool>) {
         for (k, v) in m {
             match feature_for_key(k) {
+                Some(Feature::RmcpClient) => {
+                    if k != Feature::RmcpClient.key() {
+                        self.record_legacy_usage(k.as_str(), Feature::RmcpClient);
+                    }
+                    if !*v {
+                        tracing::warn!(
+                            "[features].{k} is ignored; the RMCP client is always enabled"
+                        );
+                        continue;
+                    }
+                    self.enable(Feature::RmcpClient);
+                }
                 Some(feat) => {
                     if k != feat.key() {
                         self.record_legacy_usage(k.as_str(), feat);
@@ -190,7 +204,6 @@ impl Features {
             experimental_sandbox_command_assessment: cfg.experimental_sandbox_command_assessment,
             experimental_use_freeform_apply_patch: cfg.experimental_use_freeform_apply_patch,
             experimental_use_unified_exec_tool: cfg.experimental_use_unified_exec_tool,
-            experimental_use_rmcp_client: cfg.experimental_use_rmcp_client,
             tools_web_search: cfg.tools.as_ref().and_then(|t| t.web_search),
             tools_view_image: cfg.tools.as_ref().and_then(|t| t.view_image),
             ..Default::default()
@@ -209,7 +222,6 @@ impl Features {
                 .experimental_use_freeform_apply_patch,
 
             experimental_use_unified_exec_tool: config_profile.experimental_use_unified_exec_tool,
-            experimental_use_rmcp_client: config_profile.experimental_use_rmcp_client,
             tools_web_search: config_profile.tools_web_search,
             tools_view_image: config_profile.tools_view_image,
         };
@@ -275,6 +287,12 @@ pub const FEATURES: &[FeatureSpec] = &[
         stage: Stage::Stable,
         default_enabled: true,
     },
+    FeatureSpec {
+        id: Feature::RmcpClient,
+        key: "rmcp_client",
+        stage: Stage::Stable,
+        default_enabled: true,
+    },
     // Unstable features.
     FeatureSpec {
         id: Feature::UnifiedExec,
@@ -282,12 +300,6 @@ pub const FEATURES: &[FeatureSpec] = &[
         stage: Stage::Experimental,
         default_enabled: false,
     },
-    FeatureSpec {
-        id: Feature::RmcpClient,
-        key: "rmcp_client",
-        stage: Stage::Experimental,
-        default_enabled: false,
-    },
     FeatureSpec {
         id: Feature::ApplyPatchFreeform,
         key: "apply_patch_freeform",
@@ -343,3 +355,25 @@ pub const FEATURES: &[FeatureSpec] = &[
         default_enabled: false,
     },
 ];
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use std::collections::BTreeMap;
+
+    #[test]
+    fn rmcp_client_feature_is_always_enabled() {
+        let mut features = Features::with_defaults();
+        assert!(features.enabled(Feature::RmcpClient));
+
+        let mut map = BTreeMap::new();
+        map.insert("rmcp_client".to_string(), false);
+        features.apply_map(&map);
+
+        assert!(features.enabled(Feature::RmcpClient));
+
+        features.disable(Feature::RmcpClient);
+
+        assert!(features.enabled(Feature::RmcpClient));
+    }
+}

codex-rs/core/src/features/legacy.rs

@@ -51,7 +51,6 @@ pub struct LegacyFeatureToggles {
     pub experimental_sandbox_command_assessment: Option<bool>,
     pub experimental_use_freeform_apply_patch: Option<bool>,
     pub experimental_use_unified_exec_tool: Option<bool>,
-    pub experimental_use_rmcp_client: Option<bool>,
     pub tools_web_search: Option<bool>,
     pub tools_view_image: Option<bool>,
 }
@@ -82,12 +81,6 @@ impl LegacyFeatureToggles {
             self.experimental_use_unified_exec_tool,
             "experimental_use_unified_exec_tool",
         );
-        set_if_some(
-            features,
-            Feature::RmcpClient,
-            self.experimental_use_rmcp_client,
-            "experimental_use_rmcp_client",
-        );
         set_if_some(
             features,
             Feature::WebSearchRequest,

docs/config.md

@@ -42,7 +42,6 @@ Supported features:
 | Key                                       | Default | Stage        | Description                                          |
 | ----------------------------------------- | :-----: | ------------ | ---------------------------------------------------- |
 | `unified_exec`                            |  false  | Experimental | Use the unified PTY-backed exec tool                 |
-| `rmcp_client`                             |  false  | Experimental | Enable oauth support for streamable HTTP MCP servers |
 | `apply_patch_freeform`                    |  false  | Beta         | Include the freeform `apply_patch` tool              |
 | `view_image_tool`                         |  true   | Stable       | Include the `view_image` tool                        |
 | `web_search_request`                      |  false  | Stable       | Allow the model to issue web searches                |
@@ -53,6 +52,8 @@ Supported features:
 Notes:
 
 - Omit a key to accept its default.
+- The RMCP client is always enabled; legacy `rmcp_client` and `experimental_use_rmcp_client`
+  toggles are ignored.
 - Legacy booleans such as `experimental_use_exec_command_tool`, `experimental_use_unified_exec_tool`, `include_apply_patch_tool`, and similar `experimental_use_*` keys are deprecated; setting the corresponding `[features].<key>` avoids repeated warnings.
 
 ## Model selection
@@ -464,13 +465,9 @@ http_headers = { "HEADER_NAME" = "HEADER_VALUE" }
 env_http_headers = { "HEADER_NAME" = "ENV_VAR" }
 ```
 
-Streamable HTTP connections always use the experimental Rust MCP client under the hood, so expect occasional rough edges. OAuth login flows are gated on the `experimental_use_rmcp_client = true` flag:
-
-```toml
-experimental_use_rmcp_client = true
-```
-
-After enabling it, run `codex mcp login <server-name>` when the server supports OAuth.
+Streamable HTTP connections always use the Rust MCP client under the hood. OAuth login
+flows are supported by default; run `codex mcp login <server-name>` when the server
+supports OAuth to store credentials.
 
 #### Other configuration options
 
@@ -489,17 +486,6 @@ disabled_tools = ["search"]
 
 When both `enabled_tools` and `disabled_tools` are specified, Codex first restricts the server to the allow-list and then removes any tools that appear in the deny-list.
 
-#### Experimental RMCP client
-
-This flag enables OAuth support for streamable HTTP servers.
-
-```toml
-experimental_use_rmcp_client = true
-
-[mcp_servers.server_name]
-…
-```
-
 #### MCP CLI commands
 
 ```shell

docs/example-config.md

@@ -214,13 +214,13 @@ view_image = true
 [features]
 # Leave this table empty to accept defaults. Set explicit booleans to opt in/out.
 unified_exec = false
-rmcp_client = false
 apply_patch_freeform = false
 view_image_tool = true
 web_search_request = false
 experimental_sandbox_command_assessment = false
 ghost_commit = false
 enable_experimental_windows_sandbox = false
+# The RMCP client is always enabled; legacy toggles are ignored.
 
 ################################################################################
 # Experimental toggles (legacy; prefer [features])
@@ -229,9 +229,6 @@ enable_experimental_windows_sandbox = false
 # Use experimental unified exec tool. Default: false
 experimental_use_unified_exec_tool = false
 
-# Use experimental Rust MCP client (enables OAuth for HTTP MCP). Default: false
-experimental_use_rmcp_client = false
-
 # Include apply_patch via freeform editing path (affects default tool set). Default: false
 experimental_use_freeform_apply_patch = false
 
@@ -320,7 +317,6 @@ experimental_use_freeform_apply_patch = false
 # experimental_compact_prompt_file = "compact_prompt.txt"
 # include_apply_patch_tool = false
 # experimental_use_unified_exec_tool = false
-# experimental_use_rmcp_client = false
 # experimental_use_freeform_apply_patch = false
 # experimental_sandbox_command_assessment = false
 # tools_web_search = false