Summary

Codex Desktop currently appears able to call MCP tools, but it does not render MCP Apps inline iframe UI resources.

A minimal MCP App tool returns a valid mcp_app_resource_uri and _meta resource URI fields, but Codex Desktop never appears to call read-mcp-resource, so the inline UI is not rendered.

Can you confirm whether MCP Apps inline UI is currently supported in Codex Desktop, and if not, when it is expected to be supported?

Environment

• Codex Desktop: 26.429.30905
• Bundled Codex CLI/runtime: codex-cli 0.128.0-alpha.1
• macOS
• MCP server: local stdio server
• features.apps = true
• features.enable_mcp_apps = true was also tested

Reproduction

1. Register a local MCP server that exposes:

   • a tool: show_minimal_inline_app
   • a resource: ui://minimal-inline/hello.html

2. The tool returns a successful result with:

{
  "structuredContent": {
    "title": "Minimal MCP Inline App",
    "inline_resource_uri": "ui://minimal-inline/hello.html"
  },
  "_meta": {
    "ui/resourceUri": "ui://minimal-inline/hello.html",
    "ui.resourceUri": "ui://minimal-inline/hello.html",
    "openai/outputTemplate": "ui://minimal-inline/hello.html",
    "openai/resultCanProduceWidget": true,
    "openai/widgetAccessible": true,
    "ui": {
      "resourceUri": "ui://minimal-inline/hello.html"
    }
  }
}

1. Codex session logs show:

mcp_app_resource_uri: ui://minimal-inline/hello.html

1. However, Codex Desktop does not render an inline iframe UI and no read-mcp-resource / resource read is observed.

Expected behavior

When an MCP tool result includes a valid MCP App resource URI, Codex Desktop should read the MCP resource and render it inline as an iframe/app UI.

Actual behavior

The MCP tool call succeeds and the session log contains mcp_app_resource_uri, but the Desktop UI only shows the textual tool result. No inline app UI is rendered.

Additional investigation

I inspected the current Desktop bundle and found that MCP Apps rendering appears to be gated by enable_mcp_apps / renderMcpApps.

The public Codex docs mention features.apps, but I could not find public documentation for features.enable_mcp_apps.

The OpenAI Codex repo has PR #19884, "Add MCP app feature flag", which adds enable_mcp_apps as an under-development feature disabled by default: https://github.com/openai/codex/pull/19884

This suggests MCP Apps inline UI may currently be behind an internal/product gate, even though MCP tools and resources are otherwise available.

Question

Is MCP Apps inline UI currently supported in Codex Desktop?

If it is intentionally gated or temporarily disabled, is there a documented way to enable it locally, or an expected release/version where it will be supported?