ChatGPT plugins vs MCP server: where does Sume fit?

They are different layers. A plugin is a package; an MCP server is one of the things a plugin can contain. OpenAI's docs say plugins "can include skills and MCP servers", so a plugin can point at Sume's hosted MCP server at https://mcp.sume.com/mcp, but installing a plugin does not by itself sign anyone in to Sume.

The plugin facts come from OpenAI's plugins overview and build guide, plus the ChatGPT release notes, all read 2026-09-29. Sume's connection steps are in the MCP quickstart, which documents Claude Code and Codex or other HTTP MCP clients, and does not list ChatGPT as a client.

What is a plugin, and what is an MCP server?

OpenAI describes plugins as bundles of capabilities for reusable workflows in ChatGPT and Codex, with one universal plugin directory shared by both. An MCP server is a single endpoint that exposes tools. The plugin wraps the workflow (skills, instructions) around connections like that.

What goes in a plugin that talks to Sume?

A portable plugin has a plugin.json at the root and, if it ships MCP servers, an mcp.json file. The build guide warns not to just rename .mcp.json, because the portable MCP format also declares a transport type for each server. For Sume that transport is streamable HTTP at the URL above.

Keep credentials out of the package. Sume's quickstart says not to paste API keys into chat and to prefer the OAuth connector flow for interactive clients. On OAuth the required scope is mcp:read, which is read-only, and the Write toggle at consent adds mcp:write, as the OAuth page lays out. A plugin that shipped an API key would bypass that consent step.

# plugin root
plugin.json     # manifest
mcp.json        # declares the Sume server and its transport type
skills/         # the workflows that call Sume tools

Do I need a plugin at all?

No. In Codex you can connect Sume directly: OpenAI's MCP page says Codex stores MCP configuration in config.toml, and codex mcp add with --url plus codex mcp login sets it up. A plugin earns its place when you want to hand teammates one installable bundle of skills and the server together.

The release notes also show why the packaging matters. ChatGPT announced planned retirement of custom GPTs, with a migration path to plugins that combine reusable instructions with connected apps. That note says nothing about Sume, so treat it as background, not as a Sume integration path.