feat: hot reload mcp servers #8957

shijie-oai · 2026-01-09T05:36:30Z

Summary

Added mcpServer/refresh command to inform app servers and active threads to refresh mcpServer on next turn event.
Added pending_mcp_server_refresh_config to codex core so that if the value is populated, we reinitialize the mcp server manager on the thread level.
- The config is updated on mcpServer/refresh command which we iterate through threads and provide with the latest config value after last write.

shijie-oai · 2026-01-09T21:05:01Z

codex-rs/app-server/src/codex_message_processor.rs

        outgoing.send_response(request_id, response).await;
    }

+    async fn mcp_server_refresh(&self, request_id: RequestId, _params: Option<()>) {


This does not refresh the mcp connection manager for all active threads for inform them there is an update with the latest mcp config. It is up to the thread to refresh the connection on next active turn. This should help with performance and avoid excessive refresh if there is a lot of MCP changes at once.

Maybe put this in a comment?

"It is up to the thread to refresh the connection on next active turn."

What does this mean?

All active threads in the thread manager would be aware of a new mcp config but we are not triggering an actual reinitialization yet. On a future turn (i.e. user submit a new prompt), if the thread detects a pending_mcp_config, then it would first reinitialize and then move onto the actual turn. The benefit here is that we are not doing any extra leg work - for example you started a thread and then we change the mcp servers but never reengage with that thread, then that thread would not refresh mcp server until called upon.

shijie-oai · 2026-01-09T21:05:41Z

codex-rs/app-server/src/codex_message_processor.rs

+
+        let thread_manager = Arc::clone(&self.thread_manager);
+        tokio::spawn(async move {
+            thread_manager.refresh_mcp_servers(refresh_config).await;


We build the mcp configs and pass it along to the thread so that they can have the latest slice on next refresh.

shijie-oai · 2026-01-09T21:10:23Z

codex-rs/core/src/codex.rs

+        let mut refreshed_manager = McpConnectionManager::default();
+        refreshed_manager
+            .initialize(
+                mcp_servers,
+                store_mode,
+                auth_statuses,
+                self.get_tx_event(),
+                cancel_token,
+                sandbox_state,
+            )
+            .await;


We are doing a full reset here so that the mcp manager has the latest config value.

shijie-oai · 2026-01-09T21:42:52Z

codex-rs/core/src/codex.rs

            agent_status: Arc::clone(&agent_status),
            state: Mutex::new(state),
            features: config.features.clone(),
+            pending_mcp_server_refresh_config: Mutex::new(None),


Track if there is any pending config, if there is refresh_mcp_servers_if_requested would use it to reinitialize the mcp server.

shijie-oai · 2026-01-09T21:46:06Z

codex-rs/core/src/thread_manager.rs

        self.state.threads.read().await.keys().copied().collect()
    }

+    pub async fn refresh_mcp_servers(&self, refresh_config: McpServerRefreshConfig) {


Iterate through all active threads and submit Op::RefreshMcpServers with the latest config so that thread can pick up and reinit mcp connection managers on next turn.

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chatgpt-codex-connector · 2026-01-09T21:47:46Z

codex-rs/app-server/src/codex_message_processor.rs

+        let thread_manager = Arc::clone(&self.thread_manager);
+        tokio::spawn(async move {
+            thread_manager.refresh_mcp_servers(refresh_config).await;


Serialize refresh requests to avoid stale config

Because mcp_server_refresh spawns a detached task, two rapid mcpServer/refresh calls can run out of order. If the older refresh task is scheduled after the newer one, it will enqueue an Op::RefreshMcpServers with the stale config last, and the core handler overwrites pending_mcp_server_refresh_config on each thread with that older payload. In that scenario, threads reinitialize with the wrong MCP configuration until another refresh arrives. Consider awaiting thread_manager.refresh_mcp_servers or adding sequencing/version checks so newer config always wins.

Useful? React with 👍 / 👎.

owenlin0 · 2026-01-10T00:18:59Z

codex-rs/app-server/src/codex_message_processor.rs

+            }
+        };
+
+        let mcp_servers = match serde_json::to_value(&config.mcp_servers) {


why serialize with serde_json::to_value? these types become Value which feels less useful/descriptive than the real types.

i think self.load_latest_config() will already throw an error if it fails to read the config on disk

owenlin0 · 2026-01-10T00:20:55Z

codex-rs/core/src/codex.rs

+                    return;
+                }
+            };
+        let store_mode = match serde_json::from_value::<OAuthCredentialsStoreMode>(


owenlin0 · 2026-01-10T00:24:08Z

codex-rs/app-server/README.md

 - `model/list` — list available models (with reasoning effort options).
 - `skills/list` — list skills for one or more `cwd` values (optional `forceReload`).
 - `mcpServer/oauth/login` — start an OAuth login for a configured MCP server; returns an `authorization_url` and later emits `mcpServer/oauthLogin/completed` once the browser flow finishes.
+- `mcpServer/refresh` — reinitialize MCP servers for loaded threads and refresh cached tool lists; returns `{}`.


what's the use case? is it:

user updates mcp config in config.toml

we want to reload that config without restarting the server?

maybe worth expanding on when this should be used

watched your demo just now (lol), what do you think about calling this config/mcpServer/reload? kind of generalizes to config/<feature>/reload, or one day might be nice to have a whole config/reload

Ya I am a bit hesitant with calling it that because this method does not actually reload the config and tell active threads that there are new config and reload on the next turn.

#8957 (comment)

Actually will rename and make it clean in the readme and leave comments in code.

sounds good! yeah the fact that the actual reload is deferred feels like an implementation detail, but ultimately it's just reloading the config

shijie-oai force-pushed the shijie/hot-reload-mcp-servers branch from b0adb94 to 824fd95 Compare January 9, 2026 17:44

shijie-oai added 2 commits January 9, 2026 09:45

feat: hot reload mcp servers

8c46235

Mcp server refresh sends the latest mcp configs

238497c

shijie-oai force-pushed the shijie/hot-reload-mcp-servers branch from 824fd95 to 238497c Compare January 9, 2026 17:45

shijie-oai added 2 commits January 9, 2026 10:26

Drop McpServerRefresh params

00fdec6

cleanup

b2af85b

shijie-oai commented Jan 9, 2026

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test added

cb1ee77

shijie-oai marked this pull request as ready for review January 9, 2026 21:41

shijie-oai requested review from bolinfest, dylan-hurd-oai, gpeal and owenlin0 January 9, 2026 21:42

shijie-oai commented Jan 9, 2026

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shijie-oai requested a review from aibrahim-oai January 9, 2026 22:38

gpeal approved these changes Jan 9, 2026

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owenlin0 reviewed Jan 10, 2026

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feat: hot reload mcp servers #8957

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shijie-oai commented Jan 9, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

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shijie-oai commented Jan 9, 2026 •

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