Provider Error (ERROR_PROVIDER_ERROR) — Sonnet 5 High fails in one chat, Opus 4.8 works fine same chat

Support Bug Reports
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1

Where does the bug appear (feature/product)?

Cursor IDE

Describe the Bug

In one specific chat, every message sent with Claude Sonnet 5 High immediately fails with a non-retryable Provider Error. Switching to Opus 4.8 in the exact same chat/thread works normally.
In other new chats - Claude Sonnet 5 High will work just fine, on that particular chat - it has long history but it was working perfectly fine for more than 2 weeks. I started when I switched to Opus4.8 and back to Sonnet 5.0 after few messages. Please assist

Request ID: 9b4651ce-c85f-4ab8-9a3e-ac8366bbffdd

Steps to Reproduce

  1. Open the affected chat
  2. Select Sonnet 5 High
  3. Send any message
  4. Get Provider Error
  5. Switch to Opus 4.8 in same chat → works fine.

Operating System

Windows 10/11

Version Information

Version: 3.13.10 (system setup)
VS Code Extension API: 1.128.0
Commit: 4f02290ccd9304f0e6bf8ee85f6e9106f02ac1f0
Date: 2026-07-23T21:41:07.333Z
Layout: IDE
Build Type: Stable
Release Track: Default
Electron: 40.10.3
Chromium: 144.0.7559.236
Node.js: 24.15.0
V8: 14.4.258.32-electron.0
xterm.js: 6.1.0-beta.256
OS: Windows_NT x64 10.0.26200

For AI issues: add Request ID with privacy disabled

Request ID: 9b4651ce-c85f-4ab8-9a3e-ac8366bbffdd
{“error”:“ERROR_PROVIDER_ERROR”,“details”:{“title”:“Provider Error”,“detail”:“We’re having trouble connecting to the model provider. This might be temporary - please try again in a moment.”,“isRetryable”:false,“additionalInfo”:{},“buttons”:,“planChoices”:},“isExpected”:true}
Provider Error We’re having trouble connecting to the model provider. This might be temporary - please try again in a moment.
NonRetriableError: Provider Error We’re having trouble connecting to the model provider. This might be temporary - please try again in a moment.
at Kcb (vscode-file://vscode-app/c:/Program%20Files/cursor/resources/app/out/vs/workbench/workbench.desktop.main.js:9450:6779)
at iIr (vscode-file://vscode-app/c:/Program%20Files/cursor/resources/app/out/vs/workbench/workbench.desktop.main.js:9450:5416)
at zRm (vscode-file://vscode-app/c:/Program%20Files/cursor/resources/app/out/vs/workbench/workbench.desktop.main.js:9451:12327)
at Object.classify (vscode-file://vscode-app/c:/Program%20Files/cursor/resources/app/out/vs/workbench/workbench.desktop.main.js:9451:16859)
at Zcb (vscode-file://vscode-app/c:/Program%20Files/cursor/resources/app/out/vs/workbench/workbench.desktop.main.js:9451:5856)
at async FOa.runWithSharedTurnRunner (vscode-file://vscode-app/c:/Program%20Files/cursor/resources/app/out/vs/workbench/workbench.desktop.main.js:9451:16211)
at async Pq.runAgentLoop (vscode-file://vscode-app/c:/Program%20Files/cursor/resources/app/out/vs/workbench/workbench.desktop.main.js:12149:23038)
at async b1l.streamFromAgentBackend (vscode-file://vscode-app/c:/Program%20Files/cursor/resources/app/out/vs/workbench/workbench.desktop.main.js:18421:15130)
at async b1l.getAgentStreamResponse (vscode-file://vscode-app/c:/Program%20Files/cursor/resources/app/out/vs/workbench/workbench.desktop.main.js:18421:24972)
at async L5e.submitChatMaybeAbortCurrent (vscode-file://vscode-app/c:/Program%20Files/cursor/resources/app/out/vs/workbench/workbench.desktop.main.js:9615:2511)

Does this stop you from using Cursor

No - Cursor works, but with this issue

6

Hey there!

The short version: this is a server-side bug on our end, not your setup or your Cursor version, so there’s nothing to update or reinstall on your side. It’s triggered by switching models mid-thread (Opus 4.8 back to Sonnet 5) in a long chat. After that switch, that specific chat’s history ends up in a state Sonnet 5 rejects but Opus 4.8 still accepts, which is why Opus keeps working in the same chat while Sonnet fails instantly.

Reliable workarounds for now:

  1. Start a new chat for Sonnet 5. New chats aren’t affected, which matches what you’re seeing.
  2. In the affected chat, keep using Opus 4.8. It’ll continue to work normally.

The affected chat’s existing history can’t be fully repaired on the client side, so a fresh chat is the cleanest path for Sonnet 5 until the fix ships.

This is a known one on our side and our team is actively working on a server-side fix. Once it’s deployed you won’t need to do anything on your end, and I’ll follow up here when it lands.

7

Hey @mohitjain thanks for the update.

Since I really need my affected chat back to work with Sonnet5, in case there isn’t any workaround possible here (pls confirm) is there any ETA For this fix?

9

The failure is tied to the most recent model’s reasoning in that thread, so the trick is to make the last turn a non-Claude one before you switch back:

  1. In the affected chat, pick a non-Claude model in the model dropdown (for example Cursor’s Composer, a GPT model, or Gemini, whichever you have available).
  2. Send one short message so that model replies once.
  3. Switch back to Sonnet 5 High and carry on as normal.

I checked this end to end and Sonnet 5 started working again in the same chat with the history intact. Two notes: if you switch to Opus mid-thread again later it can come back, in which case just repeat the same step (one non-Claude reply, then back to Sonnet 5). And if a non-Claude model isn’t available to you, a fresh chat for Sonnet 5 is the reliable fallback, with Opus continuing to work in the existing chat either way.

On an ETA: I don’t have a specific timeline I can share. This is a known issue on our side and our team is aware of it and working on a fix. It’s fully server-side, so once it ships you won’t need to change anything on your end, and I’ll follow up here as soon as it lands.

10

Thanks a lot @mohitjain will try that workaround with Gemini\NonClaude model and see how it goes.

For the meantime, seems that another potential WA is to do short prompt like “here?” in opus, then switch the Sonnet5 and it returned to work (for some reason).

Hope that this issue will be resolved soon :folded_hands:

12

Hey @Amir_Tal,
The Provider Error you were hitting with Sonnet 5 High in that chat (after switching to Opus and back) should be sorted out now on our side. It was coming from that chat’s history ending up in a state Sonnet 5 wouldn’t accept once models were switched mid-thread - that’s now handled on our end, so the chat should work again with its full history, and there’s nothing you need to update. Give it another try and let me know if you still run into it.