I tested GPT-5.6 and GPT-6 with Medium → Instant → Medium. Both models failed on Instant, both succeeded on Medium. Here's what I found.

[u/echoabenteuer]

I've been investigating some serious ChatGPT reliability issues over the past several days, and my latest tests revealed something particularly interesting: Both GPT-5.6 and GPT-6 showed problems under Instant, while Medium worked in every tested run.

I'm a long-time ChatGPT power user, primarily working on long-form creative writing, software development, and projects requiring consistent context retention.

After experiencing disappearing responses, incomplete generations, and inconsistent instruction-following, I decided to run controlled A/B/A tests.

1. GPT-5.6 – Medium → Instant → Medium

• Medium (Test 1): Successful. Response completed and remained visible.
• Instant (Test 2): Failed. Generated response disappeared.
• Medium (Control Test): Successful again.

2. GPT-6 – Medium → Instant → Medium

• Medium (Test 1): Successful. All requested story events were completed.
• Instant (Test 2): Failed. Response ended prematurely, leaving explicitly requested events unfinished.
• Medium (Control Test): Successful again.

That's four successful Medium tests and two problematic Instant tests across two model generations.

Important distinction: These are two different failure symptoms. GPT-5.6 lost a generated response, while GPT-6 prematurely ended a story. I'm not claiming they necessarily share the same root cause.

Six runs aren't enough to establish causality, but the matching A/B/A pattern is worth investigating.

3. The technical evidence gets more interesting

During my earlier investigation into disappearing GPT-5.6 Sol responses, I captured the following using Chrome Developer Tools:

• Endpoint: POST /backend-api/f/conversation
• HTTP status: 200 OK
• Content type: text/event-stream
• SSE completion indicator: complete
• Generated response visible during streaming
• Assistant message disappearing immediately afterward

I also reproduced the disappearing-response behavior using GPT-5.5 in a completely new conversation.

Clearing cookies didn't resolve the issue, and I've observed related symptoms across Windows, iOS, and Android.

An HTTP 200 response and completed SSE stream don't prove successful message persistence, but they make the failure particularly interesting.

These network diagnostics are from an earlier investigation, not from the latest A/B/A tests.

4. Did OpenAI change how Instant works?

This is what I'm trying to understand.

OpenAI positions Instant as the faster option for everyday tasks, while Medium provides additional reasoning effort.

That's understandable.

But does this mean complex, long-form creative writing is now effectively better suited to Medium?

I've noticed that Medium generally completes my story prompts more reliably, but it also tends to write significantly longer responses than I actually requested.

Instant often produces a more natural length, but lately it has become unreliable in my tests.

I've even adjusted my custom instructions to explicitly require complete scenes without unnecessary length or invented plot developments.

The differences persist.

5. Support and independent reports

My investigation is already documented under OpenAI Support Case #16904787.

I've submitted screenshots, conversation URLs, network diagnostics, and reproduction details.

Other users have reported similar disappearing-response symptoms:

https://community.openai.com/t/chatgpt-web-ui-bug-entire-responses-and-download-links-disappear-until-page-reload/1404260

And broader GPT-5.6 reliability concerns:

https://community.openai.com/t/gpt-5-6-sol-has-seriously-deteriorated-the-past-week-or-so/1399353

These reports don't prove a shared technical cause, but they suggest my experience isn't entirely isolated.

6. Has anyone else tested this?

I'd genuinely appreciate results from other users.

If you have access to GPT-5.6 or GPT-6, could you try the same Medium → Instant → Medium sequence with a reasonably complex prompt?

Please note whether:

• The response completes all requested instructions.
• The generated message remains visible after completion.
• Reloading the page restores any missing content.
• Instant and Medium produce significantly different response lengths.
• The selected model and reasoning level remain unchanged.

Ideally, use the same prompt and comparable conversation conditions.

I'm especially interested in whether this behavior is specific to my account or whether others can reproduce it.

Final thoughts

I understand that different reasoning levels are supposed to behave differently.

But faster reasoning shouldn't mean disappearing answers, and reduced reasoning shouldn't mean abandoning explicit instructions halfway through.

I'm not claiming OpenAI deliberately degraded anything. I simply want to understand whether we're seeing a regression, a configuration issue, or an intentional change in how Instant is designed to handle complex tasks.

At this point, I've spent so much time documenting bugs that I'm starting to feel like an unpaid QA engineer. 😭💀

I originally just wanted to write my stories.

Now I'm comparing reasoning configurations, inspecting SSE streams, collecting request IDs, and running cross-model A/B/A tests.

OpenAI, I wanted a writing assistant, not a second career in software quality assurance. 😂

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[u/fligglymcgee]

This is a borderline hostile writing style.

[u/echoabenteuer → u/fligglymcgee]

LMAOOO, that’s just my sarcastic sense of humor. 😂💀

I can be pretty blunt, and sometimes my humor gets a little dark. My AuDHD already makes life chaotic enough, so I tend to deal with frustrating situations using sarcasm. 😂

But seriously, I’m criticizing a paid product and its reliability, not attacking anyone personally.

I’ve spent days documenting reproducible issues, collecting technical evidence, and contacting support.

If my frustration comes through in the writing, well… that’s because I’m genuinely frustrated.

A little sarcasm doesn’t invalidate the technical findings. 😅

[u/fligglymcgee → u/echoabenteuer]

You have a seriously troubling relationship with llm's and you should consider reducing your reliance on them to produce simulated personal commentary.

[u/Sircuttlesmash → u/echoabenteuer]

Is there actually human being looking at these comments and thinking yep this looks good I'll submit these comments

[u/1988rx7T2]

Instant has always sucked bro

[u/echoabenteuer → u/1988rx7T2]

LMAOOO, fair enough. 😭💀😂

But here’s the thing: Instant being less capable than Medium is one thing. Instant generating an entire response and then making it disappear like a magician is a completely different level of broken. 💀

And GPT-5.6 Instant actually worked pretty well for my long-form writing before these recent issues.

I don’t expect Instant to outperform Medium on complex tasks. I just expect it to finish what it starts and not delete its own homework. 😂

At this point, I’m not even asking for miracles. I’m asking for my damn responses to stay on the screen. 😭

[u/1988rx7T2 → u/echoabenteuer]

Instant is mostly free tier, and so if compute is short, it will get interrupted first. API is pricey so it gets highest priority.

[u/Maikel92]

We are reaching a point where 95% of people won’t need another incremental update

[u/echoabenteuer → u/Maikel92]

Fair point, but I’d rather have a reliable AI than another shiny update. Fixing existing features should come first. 😂

[u/Maikel92 → u/echoabenteuer]

Classic bug fixes update 🤣

[u/echoabenteuer → u/Maikel92]

👀

[u/zkcanuck]

Nice. Can you compare to Opus/Sonnet?

[u/xx_gamer_xx123321]

Damn

[u/echoabenteuer → u/xx_gamer_xx123321]

LMAOOO, “damn” was pretty much my reaction too when I saw the test results. 😭💀😂

I just wanted to write some stories, not accidentally become an unpaid OpenAI QA engineer investigating model routing, reasoning configurations, and disappearing responses.

At this point, I deserve a debugging salary and a vacation. 😂

[u/Sircuttlesmash → u/echoabenteuer]

You comment like you're a bot or you're just using the model to write replies for you

[u/echoabenteuer → u/Sircuttlesmash]

LMAOOO, you caught me. 😂💀

Yeah, I use AI to help write some of my replies because sometimes I’m just too lazy to type out an entire essay in English. 😭😂

The experiences, tests, screenshots, and bug reports are all mine, though. AI just helps me put my thoughts into words.

I’m already doing unpaid QA work for OpenAI. You really expect me to do all the typing myself too? 💀😂

[u/metinb83 → u/echoabenteuer]

Not enjoying writing is fine, but then just make a quick "I did this. Here's how I did it: (brief bullet points). Here's a table with the results." and done. No need to fill space with AI writing.

[u/Sircuttlesmash → u/echoabenteuer]

Help is one word to use I suppose

[u/echoabenteuer]

Good question! 😄

I’ve actually been testing Claude Sonnet 4.6 alongside Gemini, DeepSeek, and Meta AI while looking for a reliable backup to ChatGPT.

Claude Sonnet 4.6: Honestly, one of the strongest alternatives I’ve tested for long-form creative writing. It produced natural dialogue, maintained a good narrative flow, and handled my detailed story instructions surprisingly well, even with low reasoning effort.

The biggest downside for me is Anthropic’s usage limits, especially when working on long-running projects.

Claude Opus: I haven’t tested it extensively enough to give you a fair comparison yet.

One important distinction, though: My GPT-5.6/GPT-6 A/B/A tests specifically examined response retention and premature completion across Instant and Medium configurations.

I haven’t performed an equivalent controlled test with Claude, so I can’t honestly claim that Sonnet or Opus is technically more reliable based on those results alone.

What I can say is that Sonnet 4.6 has been very promising for my creative writing workflow.

For coding, I’d need additional testing before making a meaningful comparison.

At this point, my AI testing list is getting longer than the actual stories I originally wanted to write. 😭💀😂

[u/These-Weird-6003]

I'm not sure what people on here are talking about, the point is not that instant sucks it's that chatgpt is literally NOT working on certain models at all. Functionality is nearly moot.