Claude Code /mcp shows no Authenticate for a server: check the URL

If /mcp in Claude Code shows no Authenticate option for the Sume server, the entry probably has no valid URL. Claude Code 2.1.283 stopped offering Authenticate for such servers and fixed sign-in failing with an opaque SDK error for them. Remove the entry and add Sume again as an http server at https://mcp.sume.com/mcp.

The behavior is from the Claude Code changelog entry for September 25, 2026, read 2026-10-01. The Sume command is from the MCP quickstart.

What changed in 2.1.283?

The changelog says MCP sign-in for a server with no valid URL used to fail with an opaque SDK error, and that /mcp no longer offers Authenticate for such servers. A missing button is now the signal that the URL is the problem, not the OAuth step.

What does a valid Sume entry look like?

The quickstart registers Sume with one command, then signs in with a second. The entry needs the transport and the exact URL.

claude mcp remove sume
claude mcp add --transport http sume https://mcp.sume.com/mcp
claude mcp login sume

Which mistakes leave an entry without a valid URL?

The changelog does not list causes, so this table is a checklist of things to compare against the quickstart, not a list of observed failures.

What if I use an API key instead of OAuth?

Then there is nothing to authenticate in the browser. OAuth and API keys says the client sends Authorization: Bearer <SUME_API_KEY> or x-api-key, and an API-key session sees the full hosted tool set. A missing Authenticate option is expected for a header-authenticated entry; check the header instead.

How do I confirm the fix worked?

Open /mcp, confirm Sume is connected, and ask the agent to call mcp_health. The quickstart says it confirms the endpoint, the auth source and the safety posture. With OAuth, the auth source is mcp_oauth.