diff --git a/codex-rs/cli/src/mcp_cmd.rs b/codex-rs/cli/src/mcp_cmd.rs
index 0a5be0dc23..b753fbee98 100644
--- a/codex-rs/cli/src/mcp_cmd.rs
+++ b/codex-rs/cli/src/mcp_cmd.rs
@@ -17,6 +17,7 @@ use codex_core::mcp::auth::compute_auth_statuses;
 use codex_core::protocol::McpAuthStatus;
 use codex_rmcp_client::delete_oauth_tokens;
 use codex_rmcp_client::perform_oauth_login;
+use codex_rmcp_client::supports_oauth_login;
 
 /// [experimental] Launch Codex as an MCP server or manage configured MCP servers.
 ///
@@ -189,7 +190,10 @@ impl McpCli {
 
 async fn run_add(config_overrides: &CliConfigOverrides, add_args: AddArgs) -> Result<()> {
     // Validate any provided overrides even though they are not currently applied.
-    config_overrides.parse_overrides().map_err(|e| anyhow!(e))?;
+    let overrides = config_overrides.parse_overrides().map_err(|e| anyhow!(e))?;
+    let config = Config::load_with_cli_overrides(overrides, ConfigOverrides::default())
+        .await
+        .context("failed to load configuration")?;
 
     let AddArgs {
         name,
@@ -225,17 +229,21 @@ async fn run_add(config_overrides: &CliConfigOverrides, add_args: AddArgs) -> Re
             }
         }
         AddMcpTransportArgs {
-            streamable_http: Some(streamable_http),
+            streamable_http:
+                Some(AddMcpStreamableHttpArgs {
+                    url,
+                    bearer_token_env_var,
+                }),
             ..
         } => McpServerTransportConfig::StreamableHttp {
-            url: streamable_http.url,
-            bearer_token_env_var: streamable_http.bearer_token_env_var,
+            url,
+            bearer_token_env_var,
         },
         AddMcpTransportArgs { .. } => bail!("exactly one of --command or --url must be provided"),
     };
 
     let new_entry = McpServerConfig {
-        transport,
+        transport: transport.clone(),
         enabled: true,
         startup_timeout_sec: None,
         tool_timeout_sec: None,
@@ -248,6 +256,17 @@ async fn run_add(config_overrides: &CliConfigOverrides, add_args: AddArgs) -> Re
 
     println!("Added global MCP server '{name}'.");
 
+    if let McpServerTransportConfig::StreamableHttp {
+        url,
+        bearer_token_env_var: None,
+    } = transport
+        && matches!(supports_oauth_login(&url).await, Ok(true))
+    {
+        println!("Detected OAuth support. Starting OAuth flow…");
+        perform_oauth_login(&name, &url, config.mcp_oauth_credentials_store_mode).await?;
+        println!("Successfully logged in.");
+    }
+
     Ok(())
 }
 
diff --git a/codex-rs/core/src/codex.rs b/codex-rs/core/src/codex.rs
index 22b34b1cd0..68854aee18 100644
--- a/codex-rs/core/src/codex.rs
+++ b/codex-rs/core/src/codex.rs
@@ -17,6 +17,7 @@ use codex_apply_patch::ApplyPatchAction;
 use codex_protocol::ConversationId;
 use codex_protocol::protocol::ConversationPathResponseEvent;
 use codex_protocol::protocol::ExitedReviewModeEvent;
+use codex_protocol::protocol::McpAuthStatus;
 use codex_protocol::protocol::ReviewRequest;
 use codex_protocol::protocol::RolloutItem;
 use codex_protocol::protocol::SessionSource;
@@ -370,10 +371,25 @@ impl Session {
         );
         let default_shell_fut = shell::default_user_shell();
         let history_meta_fut = crate::message_history::history_metadata(&config);
+        let auth_statuses_fut = compute_auth_statuses(
+            config.mcp_servers.iter(),
+            config.mcp_oauth_credentials_store_mode,
+        );
 
         // Join all independent futures.
-        let (rollout_recorder, mcp_res, default_shell, (history_log_id, history_entry_count)) =
-            tokio::join!(rollout_fut, mcp_fut, default_shell_fut, history_meta_fut);
+        let (
+            rollout_recorder,
+            mcp_res,
+            default_shell,
+            (history_log_id, history_entry_count),
+            auth_statuses,
+        ) = tokio::join!(
+            rollout_fut,
+            mcp_fut,
+            default_shell_fut,
+            history_meta_fut,
+            auth_statuses_fut
+        );
 
         let rollout_recorder = rollout_recorder.map_err(|e| {
             error!("failed to initialize rollout recorder: {e:#}");
@@ -400,11 +416,24 @@ impl Session {
         // Surface individual client start-up failures to the user.
         if !failed_clients.is_empty() {
             for (server_name, err) in failed_clients {
-                let message = format!("MCP client for `{server_name}` failed to start: {err:#}");
-                error!("{message}");
+                let log_message =
+                    format!("MCP client for `{server_name}` failed to start: {err:#}");
+                error!("{log_message}");
+                let display_message = if matches!(
+                    auth_statuses.get(&server_name),
+                    Some(McpAuthStatus::NotLoggedIn)
+                ) {
+                    format!(
+                        "The {server_name} MCP server is not logged in. Run `codex mcp login {server_name}` to log in."
+                    )
+                } else {
+                    log_message
+                };
                 post_session_configured_error_events.push(Event {
                     id: INITIAL_SUBMIT_ID.to_owned(),
-                    msg: EventMsg::Error(ErrorEvent { message }),
+                    msg: EventMsg::Error(ErrorEvent {
+                        message: display_message,
+                    }),
                 });
             }
         }
diff --git a/codex-rs/rmcp-client/src/auth_status.rs b/codex-rs/rmcp-client/src/auth_status.rs
index 0281c0ffe8..5e32eed485 100644
--- a/codex-rs/rmcp-client/src/auth_status.rs
+++ b/codex-rs/rmcp-client/src/auth_status.rs
@@ -44,7 +44,7 @@ pub async fn determine_streamable_http_auth_status(
 }
 
 /// Attempt to determine whether a streamable HTTP MCP server advertises OAuth login.
-async fn supports_oauth_login(url: &str) -> Result<bool> {
+pub async fn supports_oauth_login(url: &str) -> Result<bool> {
     let base_url = Url::parse(url)?;
     let client = Client::builder().timeout(DISCOVERY_TIMEOUT).build()?;
 
diff --git a/codex-rs/rmcp-client/src/lib.rs b/codex-rs/rmcp-client/src/lib.rs
index 05412da184..ca99a7bb90 100644
--- a/codex-rs/rmcp-client/src/lib.rs
+++ b/codex-rs/rmcp-client/src/lib.rs
@@ -7,6 +7,7 @@ mod rmcp_client;
 mod utils;
 
 pub use auth_status::determine_streamable_http_auth_status;
+pub use auth_status::supports_oauth_login;
 pub use codex_protocol::protocol::McpAuthStatus;
 pub use oauth::OAuthCredentialsStoreMode;
 pub use oauth::StoredOAuthTokens;