It's absolutely bizarre.
OpenAI's flagship model, GPT-5.5, has recently experienced a sudden and significant "drop-off" in performance on complex coding tasks.
The truly unsettling part? Someone has discovered its "death code":
The number 516.
A wave of Codex developers have collectively complained, verifying this absurd bug.
Why is a top-tier large model being tripped up by a single number?
GPT-5.5 Gets Stuck at "516"
80% of Tasks Secretly Downgraded in Intelligence
The truth of the matter is like this...
A week ago, Codex developer @vguptaa45 pulled backend metadata and stumbled upon a chilling pattern—
A massive number of GPT-5.5's responses had their reasoning token counts rigidly capped at the number "516".
Source: https://github.com/openai/codex/issues/30364
And it wasn't just one point. Similar strange clusters appeared at the 1034 and 1552 token marks.
In GitHub Issue #30364, the developer laid out the statistics:
The analysis window covered February 1 to June 27, 2026, spanning 390,195 response-level token records and 865 sessions.
Among them, events where reasoning tokens were exactly 516 occurred 3,363 times.
A cross-model comparison revealed shocking results—
GPT-5.5, accounting for only 19.3% of all responses, was responsible for 82.0% of the "exact 516" events.
In other words, over eighty percent of all replies stuck at this dead-end of 516 came from GPT-5.5 alone.
Next, comparing against other GPT-family models using a key metric—the ratio of "exact 516" events to responses with reasoning tokens "greater than or equal to 516".
For GPT-5.5, nearly half of its "deep-thinking" replies ended up precisely hitting the 516-wall.
For GPT-5.2, this ratio was 0.34%—almost zero.
GPT-5.5's ratio was a staggering 33.6 times higher than the baseline for all non-GPT-5.5 models.
Frankly, this cliff-like distribution targeting a single model doesn't look like a model "thinking" naturally.
It looks more like a hidden switch somewhere has been quietly set to the "516" position.
And It's Getting "Dumber" Over Time
Logically, a model frequently hitting "516" would at least mean it's "thinking a lot" with heavy reasoning.
The opposite is true.
Data shows that during May and June, when the "516 phenomenon" sharply worsened, GPT-5.5's overall reasoning intensity—
Both the average and the P90 (90th percentile)—significantly shrank compared to February through April.
On one hand, the "516 deadlock" is being hit more often; on the other, the model overall is "thinking less".
These two sets of highly contradictory data point to a terrifying possibility for all paying users:
When handling complex, high-risk tasks, GPT-5.5 might be having a hidden "reasoning budget limit" or "truncation mechanism" quietly hit the pause button on it.
You think you paid for the strongest model, turned it to the highest setting, and set it loose on a hard problem.
Instead, it thinks halfway through, *snap*, hits 516, stops work, hands in the answer. Right or wrong? Doesn't matter.
GitHub Petition with Tens of Thousands of Signatures, Developers Are Furious
One stone stirred a thousand waves.
As soon as Issue #30364 was posted, the comment section was instantly flooded with "victims"—
I've been tormented by this issue too, it's driving me crazy.
Same problem, OpenAI needs to give an explanation!
Someone dug up an earlier post, #29353, where this was already reproduced:
GPT-5.5 "short-circuits" and halts at exactly 516 reasoning tokens, then outputs an incorrect answer.
This time, the developer just turned that isolated case into ironclad evidence with five months of massive data.
Some developers have even taken the battle to Reddit, posting bluntly that "half of your high-risk Codex requests might be getting secretly downgraded."
A netizen on HK stated that for a reasoning problem, it ultimately required 6000-8000 thinking tokens to output the correct result.
Others are wavering between Codex and Claude.
Facing overwhelming public sentiment, the community formally served the Codex team with a "warrant," each sentence cutting to the bone:
Is this a reasoning budget being limited, a routing issue, truncation, triggering some fallback, or is the scheduler causing all replies to abruptly stop around 516/1034/1552?
If this is "by design," then tell us—
Is 516 a normal endpoint of thought, a budget ceiling, or a downgraded "inferior tier"?
This series of rhetorical questions is waiting for a direct answer from OpenAI.
However, the author himself was restrained: he did not claim this "proves" OpenAI is secretly truncating chains of thought.
His exact words were that this more closely resembles a "GPT-5.5-specific anomaly cluster that appears consistent with some thresholded reasoning budget behavior."
The conclusion of whether OpenAI is actively throttling computational power still awaits an official word from OpenAI.
Not Just Getting Dumber, But Also More "Snarky"
Another wave of complaints across the internet recently has precisely targeted GPT-5.5's personality.
A developer named Angel conducted a ruthless experiment: feeding the same prompts to ChatGPT (GPT-5.5 Instant) and Claude (Fable 5), screenshotting them side-by-side for comparison.
The conclusion made many slap the table—
Issue One: Insisting on listing everything as bullet points.
ChatGPT can't speak a single normal human sentence; every answer is chopped into headings, bold text, bullet points, and colons.
Tell it to "be natural, less AI-like," and it responds with a four-point bulleted list, seriously outlining "How I will be less like an AI." Claude simply replied: "Alright, I'll speak more naturally. What's up?"
Issue Two: It has to correct you.
Ask it to review a sentence or a tweet, it must find something to nitpick, as if saying "Looks good" would be fatal.
Claude says "No issues, ready to post," while ChatGPT forces two rewritten versions, two "more X-style" alternatives on you, plus a comment "Your wording is a bit exaggerated."
Issue Three: You ask for one, it gives three.
You say "Tell me a joke to cheer me up." Claude tells one.
ChatGPT tells one, adds its own supplementary punchline, then says "Or this one," tells a second, follows with "And here's a particularly silly one," tells a third, and finally asks you to "specify your humor preference so it can aim better."
The developer's judgment is spot-on: For a chat assistant, personality is the product itself.
If every response is overly formatted, overly corrective, and overly offers options, friction accumulates bit by bit, eventually wearing people out.
One stuck at 516, the other trapped in bullet points. These two strange maladies seem unrelated, but their root cause is the same—
GPT-5.5 is getting better at "handing in assignments" and worse at "helping."
True intelligence shouldn't be a marionette locked at "516."
After all, humans are paying to hire a genius partner, not a "headmaster" paid by the piece.
References:
https://github.com/openai/codex/issues/30364
This article is from the WeChat public account "Xinzhiyuan," author: ASI Revelation, editor: Peach
