You select a chunk of code, press Cmd-K, type “extract this into a function,” and the small inline popup spins. Twenty seconds. Forty. A minute. No diff appears, no error message, no way to commit the edit. Hitting Cmd-K again either layers a new popup on top or silently does nothing. The Cmd-K flow is simpler than Composer or Agent — it is a single-turn request to the model that returns a unified diff — so when it hangs it is almost always one of four things: the model API timed out silently, the context window blew up because of the surrounding file size, a stale streaming socket from the previous request, or a known-bad model selection (some old preview models drop the diff format on long inputs).
Common causes
Ordered by hit rate, highest first.
1. Model API request silently timed out
The Cursor backend has a per-request budget around 60 seconds for Cmd-K. If the upstream model (Anthropic, OpenAI, your custom) does not return in time, the response simply never arrives. The popup keeps spinning because Cursor never gets an error frame.
How to judge: Press Cmd-K on a tiny one-line change in a small file. If that also hangs, it is not your context — it is the request lane.
2. Selection plus surrounding context exceeded the model window
Cursor sends the selection plus a window of surrounding lines (and sometimes related files). On a 4000-line file with @codebase enabled, the prompt can blow past the model’s input limit. Some models truncate, some just stall.
How to judge: Try the same edit on a 50-line scratch file. Works there but not in the big file = context size.
3. Stale streaming socket from a previous Cmd-K
If you cancelled a previous Cmd-K mid-stream, the underlying socket can stay open in a half-closed state. The next request piggybacks on the dead socket and never completes.
How to judge: Cmd+Shift+P → “Developer: Reload Window.” If the next Cmd-K works, that was it.
4. Selected model has degraded or dropped the diff format
Some model versions (early Claude Haiku, deprecated OpenAI previews) return prose instead of the structured diff Cursor expects. Cursor waits for the diff that never comes.
How to judge: Settings → Models → switch to a known-good model like claude-sonnet-4.6 or gpt-5.5. Retry Cmd-K. Works = model was bad.
5. Network proxy or firewall is buffering the response
Corporate proxies that buffer entire responses before forwarding will hold the stream until completion or timeout, making the popup look hung even when the request is actually in flight.
How to judge: Disable the proxy or switch off VPN, retry. If it returns instantly, the proxy was buffering.
6. Cursor account hit a rate limit silently
If you blew through your fast-request quota mid-session, some Cursor versions queue without surfacing the wait. The popup looks hung; it is actually waiting in line.
How to judge: Open Cursor Settings → Usage. If “Fast requests used” is at the cap, that is the queue.
Before you start
- Save the file first; if the edit eventually lands, you do not want to lose other changes.
- Know which model you selected for Cmd-K (it can differ from Composer’s model).
- Have a tiny scratch file ready to isolate context-size issues.
Information to collect
- Cursor version (Help → About).
- OS.
- Model currently selected for Cmd-K (the dropdown next to the input).
- File size and selection size where it hangs.
- Whether
@codebaseor@filementions are active in the prompt. - Network setup: VPN, proxy, corporate firewall.
- Latest log line in
~/.cursor/logs/matchingcmdkorinline.
Step-by-step fix
Step 1: Cancel and reload the window
Press Escape to close the popup. Cmd+Shift+P → “Developer: Reload Window.” This kills any stale streaming socket. Retry Cmd-K on the same selection.
Step 2: Try a smaller selection and shorter prompt
Select 10 lines instead of 200. Type a 3-word instruction instead of a paragraph. If it returns quickly, the original request was too big or too ambiguous; break the change into two Cmd-K calls.
Step 3: Switch the Cmd-K model
In the Cmd-K popup, click the model dropdown. Pick claude-sonnet-4.6 or gpt-5.5 if you were on something else. Some preview models are flaky for Cmd-K specifically.
Step 4: Check status page
Open status.cursor.com and the upstream provider’s status. If either reports degraded inference, every Cmd-K will hang. Nothing to fix locally — wait or use a different provider.
Step 5: Bypass proxies temporarily
If you are on a corporate network, switch to a hotspot or disable the VPN and retry. A returned diff in 5 seconds confirms the proxy was buffering. Long-term, ask IT to allowlist api.cursor.sh and your model provider as streaming endpoints.
Step 6: Check your fast-request usage
Settings → Usage. If you are over the fast cap, either wait for the reset, upgrade the plan, or switch the Cmd-K model to one that uses slow requests (still works, just queued differently).
Step 7: Restart Cursor cleanly
Cmd+Q to fully quit (closing the window keeps the process). Relaunch, open the same file, retry. A fresh process clears any state that survived “Reload Window.”
Verify
- Run Cmd-K on a 5-line selection with a 3-word instruction. Should return in under 10 seconds.
- Repeat on a 100-line selection. Should return in under 30 seconds.
- Try the prompt that originally hung. If it now returns, you are good; if it still hangs, the prompt itself is too ambiguous — rewrite it more concretely.
- Commit a small edit through Cmd-K end to end (preview, accept).
Long-term prevention
- Keep your “Cmd-K model” setting on a stable production model, not a preview.
- For files over 2000 lines, use Composer instead of Cmd-K; Composer handles long context better.
- Avoid
@codebaseinside Cmd-K — it is meant for Composer and bloats the inline request. - Periodically reload the Cursor window during long sessions; sockets accumulate.
- If you work behind a corporate proxy, push for an allowlist rather than fighting buffering every day.
Common pitfalls
- Hitting Cmd-K a second time while the first is still spinning. You get two requests in flight and neither finishes cleanly.
- Selecting an entire 3000-line file and asking for a global refactor. Cmd-K is for surgical edits; use Composer.
- Pasting a long prompt with multiple instructions. Cmd-K does best with one clear ask.
- Assuming the spinner means progress. It does not — it is just a UI element waiting on an HTTP response that may never come.
- Ignoring the model dropdown in the popup. Each new Cmd-K session can land on a different default.
FAQ
- What is Cmd-K supposed to do? Take a selection plus a short instruction and return an inline diff you can accept or reject without leaving the editor.
- Why is it different from Composer? Cmd-K is single-turn, tightly scoped to the selection. Composer is multi-turn, can edit multiple files, and holds context across the chat.
- Can I retry without losing the prompt? Press Escape, then Cmd-K again. The prompt history is preserved in the popup’s up-arrow.
- Does Cmd-K count toward fast-request quota? Yes, every Cmd-K is one request against your plan.
- Is there a keyboard shortcut to cancel a stuck Cmd-K? Escape closes the popup. There is no “cancel and free the request” — under the hood the HTTP call may still be in flight until its server-side timeout.