Antigravity Hub still fails to connect to Roblox StudioMCP (server/discover handshake error) — persists across 2.4.3, 2.5.0, and 2.8.0

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Summary

Antigravity Hub cannot connect to Roblox StudioMCP. The exact same MCP configuration connects successfully in Antigravity IDE, so this appears to be Hub-specific. This has now been reported across at least three separate Hub versions (2.4.3, 2.5.0, and 2.8.0) with no fix so far.

Environment

  • Windows 11
  • Antigravity Hub 2.8.0
  • Roblox StudioMCP (latest, installed via Roblox Studio’s built-in Assistant Settings → MCP Servers)
  • Roblox Studio confirms the MCP server is enabled and shows active connected clients

Error:
Error: expect initialized request, but received: Some(Request(JsonRpcRequest { jsonrpc: JsonRpcVersion2_0, id: Number(1), request: CustomRequest(CustomRequest { method: “server/discover”, params: Some(Object {}), extensions: Extensions }) }))
: connection closed: calling “initialize”: client is closing: EOF

MCP configuration used:
{
“mcpServers”: {
“Roblox_Studio”: {
“command”: “cmd.exe”,
“args”: [
“/c”,
“cd /d %LOCALAPPDATA%\Roblox && .\mcp.bat”
],
“disabled”: false
}
}
}

This matches the official config shown in Roblox Studio’s own “Setup instructions” panel under Assistant Settings.

What I’ve tested

  • Confirmed mcp.bat and StudioMCP.exe work correctly in isolation (ran mcp.bat manually via PowerShell — it launches and idles correctly, waiting on stdio as expected)
  • Verified StudioMCP.exe path is correct and the executable exists
  • Confirmed Roblox Studio itself shows “Enable Studio as MCP server” ON with active connected clients
  • Same exact mcp_config.json connects successfully in Antigravity IDE
  • Fully restarted both Antigravity and Roblox Studio between tests
  • Issue reproduces consistently across Hub 2.4.3, 2.5.0, and 2.8.0
  • The only workaround found (via this forum) is downgrading Hub to 2.2.1, which resolves it completely — but 2.2.1 predates Gemini 3.7 Flash, so there is currently no Hub version that has both a working Roblox MCP connection and access to the latest models.

Why this matters

This isn’t a niche edge case — a large number of Roblox developers use Antigravity specifically for Studio MCP integration, building and iterating on scripts, systems, and game logic directly against a live Studio session. Because this bug is Hub-specific and has now persisted across multiple release cycles, it’s effectively forcing the Roblox dev community to choose between staying on an old, unsupported Hub version indefinitely, or losing Roblox MCP functionality entirely just to access current models.

I’m personally hitting this directly: I want to use Gemini 3.7 Flash, but it’s only available after upgrading Hub — and every version I’ve upgraded to since 2.4.3 breaks the Roblox connection. So right now I’m stuck choosing between the new model and my actual workflow, with no version that gives me both. Given how central Studio MCP is to this workflow, a root-cause fix would make a real difference for a lot of us building on Roblox.

Happy to provide logs, a screen recording, or any other debugging info if it helps narrow this down.

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