Feature Request: Add HTTP Streamable transport support for remote MCP servers

[chindris-mihai-alexandru]

Summary

The current type: "remote" MCP configuration only supports SSE (Server-Sent Events) transport. However, the MCP protocol now includes HTTP Streamable transport (also called http or streamable-http), which is used by several major MCP servers including Sanity.

Problem

When configuring Sanity's hosted MCP server:

{
  "mcp": {
    "sanity": {
      "type": "remote",
      "url": "https://mcp.sanity.io",
      "oauth": {}
    }
  }
}

OpenCode fails with:

SSE error: Non-200 status code (405)

This is because Sanity uses HTTP Streamable transport, not SSE. The 405 "Method Not Allowed" occurs because OpenCode sends a GET request expecting SSE, but Sanity expects POST requests for HTTP streaming.

Current Workaround

Using mcp-remote as a local proxy:

{
  "mcp": {
    "sanity": {
      "type": "local",
      "command": ["npx", "-y", "mcp-remote", "https://mcp.sanity.io", "--transport", "http-only"],
      "timeout": 60000
    }
  }
}

This works but adds unnecessary overhead and complexity.

Proposed Solution

Add native support for HTTP Streamable transport in remote MCP configuration:

{
  "mcp": {
    "sanity": {
      "type": "remote",
      "transport": "http",  // or "streamable-http"
      "url": "https://mcp.sanity.io",
      "oauth": {}
    }
  }
}

Or alternatively, a new type:

{
  "mcp": {
    "sanity": {
      "type": "http",  // new type alongside "remote" (SSE) and "local"
      "url": "https://mcp.sanity.io",
      "oauth": {}
    }
  }
}

Reference

Other MCP clients already support this:

• Claude Code: claude mcp add -t http sanity https://mcp.sanity.io
• Cursor: { "type": "http", "url": "https://mcp.sanity.io" }
• VS Code: { "type": "http", "url": "https://mcp.sanity.io" }

See: https://www.sanity.io/docs/compute-and-ai/mcp-server

Environment

• OpenCode version: 1.1.14
• macOS version: 15.7.4
• Affected MCP server: Sanity (https://mcp.sanity.io)