Grok BotKnown issues
Missing MCP-Protocol-Version header on reused MCP sessions
If your remote MCP server returns empty 400s, have it fall back to the session's negotiated version until Grok Bot is fixed.
- Status: Open. Staff confirmed it at 2:10 PM ET on Oct 8 and passed a suggested fix to the team. No fix had shipped as of 7:30 PM ET.
- First seen: Oct 8, in a forum report posted at 1:36 PM ET.
- Symptoms: Sign-in and the first tool list work, then tool calls to your remote MCP server fail with an empty HTTP 400.
- Workaround: Have the server accept requests without the header. For T3 Code, update to the build with the Effect 4.0.2 compatibility fix.
When Grok Bot reuses an existing remote MCP session, later requests leave out the MCP-Protocol-Version header. A strict server rejects those requests, so tool calls fail.
Colin, a Cursor community support engineer, confirmed it. "When Grok Bot reuses an existing MCP session, it doesn't restore the negotiated protocol version," he wrote.
Why it matters#
This affects people who add their own MCP servers to Grok Bot, under Settings, Plugins. Built-in plugins aren't mentioned in the report.
How to use it#
- Don't rely on reconnecting. Staff said a fresh connection gets reused the same way.
- If you use T3 Code, the server in the report, update it. Staff said its build with the Effect 4.0.2 compatibility fix accepts requests without the header.
- If you run your own server, the MCP spec says a server that gets no version header can use the version negotiated at initialization, or assume 2025-03-26.
Good to know#
- The spec says clients must send the header, so this is a Grok Bot bug, not your server's fault.
- There's no Grok Bot release note for a fix yet.
