Why does GitHub Copilot Claude prompt get "cut off"?

[garretwilson]

I'm constantly seeing Claude indicate that part of some input or prompt is "cut off". Is this just some artifact of how Claude "thinks", or is there a bug somewhere that actually is truncating my prompt?

Here is an example with Claude Opus 4.8, with thinking effort set to "Max".

Prompt

So ideally we should have one 16-count semaphore for file reads, and one 50-count semaphore for S3 requests? Is it easy to poinpoint exactly those I/O operations and network requests? If we do so, it is OK to let all the other network requests and I/O operations grow unbounded?

Thinking

(Bold emphasis added.)

The user is asking three specific questions about semaphore configuration and implementation. First, they want me to confirm whether a 16-count semaphore for file reads and a 50-count semaphore for S3 requests is the right approach. Second, they're asking how feasible it is to identify and wrap those exact I/O operations and network requests with semaphore acquire/release calls. Third, the question cuts off but seems to be heading toward implementation details.

In the particular case above, the response contained a complete answer to the third question I provided, so maybe that "cut off" verbiage is just an artifact of some "thinking" technique Claude uses.

I continually see this. The pattern is always something along the lines of, "The user seems to be asking about X, but then it cuts off." I just want to make sure GitHub Copilot isn't cutting something off. Or maybe GitHub Copilot cuts off the prompt when it summarizes and gives it to some subtask or some less-capable model for feeding back into Claude? It's puzzling and I just want to make sure everything is working properly (especially when I'm paying what I'm paying for Claude Opus 4.8 on Max level).

Version: 1.125.1 (user setup)
Commit: fcf604774b9f2674b473065736ee75077e256353
Date: 2026-06-19T08:39:34Z
Electron: 42.2.0
ElectronBuildId: 14159160
Chromium: 148.0.7778.97
Node.js: 24.15.0
V8: 14.8.178.14-electron.0
OS: Windows_NT x64 10.0.26200

[garretwilson]

Here's another example from Claude Opus 4.8 "thinking":

The user is asking whether anything in the specification needs clarification or correction based on our discussion, and they're leaning toward leaving the default case behavior to individual teams rather than mandating it—though they seem to be cutting off mid-thought about what specifically needs reviewing.

It's very curious this business of "they seem to be cutting off mid-thought". It is definitely a pattern that is continually surfacing. Again I'm merely wanting to ascertain whether this is some artifact of Claude reasoning or if some information is actually being "cut off" when being passed to the model.

[garretwilson]

Here's another interesting one:

… The thinking cuts off mid-word after mentioning "rotul," so there's more to consider here. …

In this case, "rotulus" is a CSS component in my Guise Skeleton library which we were updating documentation for. It would seem that the word "rotulus" was indeed "cut off" somehow internally in some subprocess of thinking.

[garretwilson]

Here is another example where Claude Opus 4.8 thinks that a readme file is cut off:

I'm looking at the README for Guise Mummy and need to fix the "Defining Navigation" section. The first paragraph has an error where it cuts off mid-sentence when describing how to control menus explicitly with a .navigation.lst file.

In this case the sentence in that section in the readme in question did not cut off mid sentence.

So it's very puzzling why Claude's thinking sees things "cut off" all around it.

[garretwilson]

I'm noting these occurrences, not to be naggy about this ticket, but because this ticket seems an appropriate place to log the variations I see in order to get some sense of where this is coming from. I'm not implying this ticket has any urgency.

Here's a variation that mentions "thought", so maybe it is some internal Claude reasoning technique or artifact:

The user wants to explore two changes: first, centering the tagline while keeping the second line left-aligned by potentially moving the layout-marquee styling to individual child elements or wrapping the tagline in its own container, and they're asking me to assess if this improves the visual presentation. Second, they're starting to mention adding their name (…) but the thought cuts off there.

[garretwilson]

Here are some more interesting examples with Claude Sonnet 5.

In one case, it claimed its thinking "trails off".

In another, it said (emphasis added):

Now I need to address the VS Code extension question carefully, since the user seems to be asking whether they should install a TypeScript 7 extension and what happens if VS Code bundles it in the future, though my research on VS Code's current TS7 support was cut off.

This is beginning to look more and more like some sort of internal Claude thinking process. Whatever is behind it may be interesting. I'll log a few more of these; then when I have time I'll try to research what is is going on, write a blog article on it, and then close this ticket.

If you know what is going on, you might mention it to point me in the right direction. Otherwise, there doesn't seem to be any behavior problem or bug to address in this ticket.

[garretwilson]

Ah ha! With Claude Sonnet 5:

I'm realizing the thought cuts off mid-sentence, but it seems I was concluding that despite the investigation, this particular feature isn't available at the CLI level.

This does seem to indicate that there are some sort of various internal sub-responses that can get truncated and perhaps fed into some larger evaluation. It's starting to look like this is some internal Claude thinking process.