BUG: "Waiting for extension host" & Severe Performance Degradation (Cursor Pro + BYOK Claude)

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1

For the past few days, Cursor has become nearly unusable across multiple repositories. I am experiencing extreme latency in AI responses and frequent “Waiting for extension host…” hangs. This occurs even when using Composer 2.

Environment & Setup:

  • Plan: Cursor Pro

  • Model/API: Claude models via custom Anthropic API Key (BYOK)

  • Scope: Multiple repositories (not repo-specific)

Symptoms:

  • AI response times have increased significantly.

  • Frequent “Waiting for extension host” status message, often leading to a complete hang.

  • General UI lag and performance degradation that wasn’t present a week ago.

Troubleshooting Done:

  • Switched between standard Chat and Composer 2 (same result).

  • Verified Anthropic API key is valid and has credits.

  • Tested across different codebases to rule out local environment issues.

Is there a known issue with the current build regarding Extension Host stability or specifically with the BYOK Anthropic integration? Any help or acknowledgment of a fix in progress would be appreciated.

2

Hi there!

We detected that this may be a bug report, so we’ve moved your post to the Bug Reports category.

To help us investigate and fix this faster, could you edit your original post to include the details from the template below?

Bug Report Template - Click to expand

Where does the bug appear (feature/product)?

  • Cursor IDE
  • Cursor CLI
  • Background Agent (GitHub, Slack, Web, Linear)
  • BugBot
  • Somewhere else…

Describe the Bug
A clear and concise description of what the bug is.

Steps to Reproduce
How can you reproduce this bug? We have a much better chance at fixing issues if we can reproduce them!

  1. …
  2. …
  3. …

Expected Behavior
What is meant to happen here that isn’t working correctly?

Screenshots / Screen Recordings
If applicable, attach images or videos (.jpg, .png, .gif, .mp4, .mov)

Operating System

  • Windows 10/11
  • MacOS
  • Linux

Version Information

  • For Cursor IDE: Menu → About Cursor → Copy
  • For Cursor CLI: Run agent about in your terminal
IDE:
Version: 2.xx.x
VSCode Version: 1.105.1
Commit: ......

CLI:
CLI Version 2026.01.17-d239e66

For AI issues: which model did you use?
Model name (e.g., Sonnet 4, Tab…)

For AI issues: add Request ID with privacy disabled
Request ID: f9a7046a-279b-47e5-ab48-6e8dc12daba1
For Background Agent issues, also post the ID: bc-…

Additional Information
Add any other context about the problem here.

Does this stop you from using Cursor?

  • Yes - Cursor is unusable
  • Sometimes - I can sometimes use Cursor
  • No - Cursor works, but with this issue

The more details you provide, the easier it is for us to reproduce and fix the issue. Thanks!

5

Bug Report

Where does the bug appear?

  • [X] Cursor IDE

  • [ ] Cursor CLI

  • [ ] Background Agent

  • [ ] BugBot

Describe the Bug

The IDE has become completely unusable over the past few days. I am experiencing severe performance degradation, extreme latency in AI responses, and frequent hangs accompanied by the message “Waiting for host extension…” This occurs across multiple different repositories and is not limited to a single project.

Steps to Reproduce

  1. Open any repository in Cursor.

  2. Initiate a prompt via Chat or Composer 2 (using Claude models via Anthropic API Key).

  3. The IDE hangs, showing “Waiting for host extension.”

  4. UI becomes unresponsive or takes an excessive amount of time to return a completion.

Expected Behavior

The Extension Host should remain stable, and AI responses should be delivered with standard latency without hanging the IDE.

Operating System

  • [X] MacOS (Darwin arm64 24.1.0)

  • [ ] Windows

  • [ ] Linux

Version Information

  • Version: 3.2.11

  • VSCode Version: 1.105.1

  • Commit: e9ee1339915a927dfb2df4a836dd9c8337e17cc0

  • Date: 2026-04-24T14:36:47.933Z

  • Electron: 39.8.1

  • Chromium: 142.0.7444.265

  • Node.js: 22.22.1

  • V8: 14.2.231.22-electron.0

AI Issue Details

  • Model Used: Claude 4.7 Opus (via Anthropic API Key) & Composer 2

  • Request ID: d9131555-b315-4a67-95ae-a40df313c324

Additional Information

I am a Cursor Pro user using BYOK (Anthropic). The issue persists even when switching to Composer 2. It feels like a regression in how the Extension Host manages the connection or indexing in the latest build.

Does this stop you from using Cursor?

  • [X] Yes - Cursor is unusable

  • [ ] Sometimes

  • [ ] No