Agent Stream Start Failed – Unable to start agent session

[Leo_Clay]

Where does the bug appear (feature/product)?

Cursor IDE

Describe the Bug

I encountered an error in Cursor when trying to start an Agent session.

An error banner appears at the top of the window with the following message:

Agent Stream Start Failed
The agent stream failed to start. Please reload the window to continue.

Additional details shown in the UI:
• Copy Request Details ID: 24d0d735-78ce-40bf-9cf5-7b13ddf06af7
• Model selected: Sonnet 4.5
• Mode: Agent
• The agent does not start at all (fails immediately before any task is executed)

Observed behavior:
• The agent session cannot be initialized
• No response or execution begins
• The error appears instantly

What I have tried:
• Reloading the window
• Restarting Cursor
• Starting a new chat / agent session

Question:
• What could cause the agent stream to fail during initialization?
• Is this related to network / proxy / extension host issues?

Steps to Reproduce

1.	Open Cursor normally.
2.	Open any project or workspace.
3.	Try to start the Agent (e.g., click Plan or send a prompt in Agent mode).
4.	Wait for the agent to start streaming.

Screenshots / Screen Recordings

Operating System

MacOS

Version Information

Version: 2.4.28 (Universal)
VSCode Version: 1.105.1
Commit: f3f5cec40024283013878b50c4f9be4002e0b580
Date: 2026-02-03T00:56:18.293Z
Build Type: Stable
Release Track: Default
Electron: 39.2.7
Chromium: 142.0.7444.235
Node.js: 22.21.1
V8: 14.2.231.21-electron.0
OS: Darwin arm64 25.2.0

For AI issues: which model did you use?

Sonnet4.5、Opus 4.6

For AI issues: add Request ID with privacy disabled

Request ID: 24d0d735-78ce-40bf-9cf5-7b13ddf06af7
{“error”:“ERROR_EXTENSION_HOST_TIMEOUT”,“details”:{“title”:“Agent Stream Start Failed”,“detail”:“The agent stream failed to start. Please reload the window to continue.”,“isRetryable”:false,“shouldShowImmediateError”:true,“additionalInfo”:{},“buttons”:[{“label”:“Reload Window”,“reloadWindow”:{}}],“planChoices”:}}
Agent Stream Start Failed [deadline_exceeded]
ConnectError: [deadline_exceeded] Agent Stream Start Failed
at vscode-file://vscode-app/Applications/Cursor.app/Contents/Resources/app/out/vs/workbench/workbench.desktop.main.js:11433:39577

Does this stop you from using Cursor

Yes - Cursor is unusable

[deanrie]

Hey, it looks like this is an issue where the extension host hangs while initializing the agent, which causes ERROR_EXTENSION_HOST_TIMEOUT / deadline_exceeded. The team is aware and tracking it.

Here are a few things you can try:

1. Disable MCP servers
   If you have them set up, turn them all off in Cursor Settings > Tools & MCP, then restart Cursor. MCP servers can cause the extension host to hang during init.

2. Start without extensions
   Run this in Terminal:

   /Applications/Cursor.app/Contents/MacOS/Cursor --disable-extensions
   

   If this helps, re-enable extensions one by one to find the problematic one.

3. Clear the databases (back up first):

   • Fully quit Cursor
   • Delete or rename the global DB: ~/Library/Application Support/Cursor/User/globalStorage/state.vscdb
   • You can also clear workspace data: ~/Library/Application Support/Cursor/User/workspaceStorage/{workspace hash}
   • Restart Cursor (you’ll need to sign in again)

4. If nothing helps
   Try rolling back to a previous version: Download · Cursor.

Related reports and fixes:

• Agent-execution-time-out (accepted answer with direct download links)
• After last update, stuck at "Waiting for extension host"

Let me know what worked and what didn’t.

[aeyarr]

@deanrie Do we have an update on this? I am stuck in a situation where I cannot close my Cursor or restart my machine as it will auto update.

[deanrie]

Hey @aeyarr, the team is aware and is tracking the issue. We don’t have an exact ETA yet, but reports like this help us prioritize.

About auto-update, can you clarify your situation? Are you on a version that works right now, and worried that restarting will force-update you to a broken version?

A couple options:

1. You can download a specific version directly from Cursor · Download so you can pick the one that works for you.
2. If the issue happens on your current version, try the workarounds from my previous message like disabling MCP servers, starting without extensions, or clearing the state database.

Also, what version are you on right now, and what OS are you using? That’ll help narrow this down.