GPTinf is an AI humanization tool that launched in the early wave of anti-detection products, around 2023-2024. The pitch is simple: paste your AI-generated text, click a button, and get back a version that's supposed to fly under the radar of AI detectors.

The interface is about as minimal as they come, and honestly, that's part of its appeal. No confusing settings, no endless mode selectors — just paste and go. It offers 8 rewriting modes (Standard, Simple, Academic, Formal, and others), a Freeze Keywords feature that protects specific terms from being altered, a Compare Mode for side-by-side original vs. rewritten text, and a built-in AI detector so you can check your output before submitting.

Here's what you won't find easily: who actually makes GPTinf. There's no founder name publicly listed anywhere. No headquarters location. No Crunchbase profile. No PitchBook listing. The LinkedIn page exists but contains no substantive information. The support email uses both a professional domain (support@gptinf.com) and a Gmail address (team.gptinf@gmail.com) in different sections of the site. Multiple independent reviewers flag this lack of transparency as a red flag — and when you're trusting a tool with sensitive academic or professional content, knowing who's behind it matters.

GPTinf built its reputation when the competition was thin. Back in 2023, there weren't many options. If you needed a humanizer, GPTinf was one of the few games in town. But the market has exploded since then. New tools have launched with more sophisticated approaches, and the detectors themselves have gotten significantly smarter — Turnitin launched dedicated AI paraphrasing detection in July 2024 and humanizer detection in August 2025. The question isn't whether GPTinf *was* good. It's whether it's still good enough.

We don't guess. We test. Our methodology is the same one we use for every humanizer review: we took a 1,000-word essay generated by GPT-5 on a standard academic topic and ran it through GPTinf. Then we checked the output against 5 major AI detectors: Turnitin, GPTZero, Originality.ai, Copyleaks, and ZeroGPT.

We recorded the AI detection score before and after humanization, giving us a clear bypass rate for each detector. But bypass rate alone doesn't tell you much if the output reads like garbage. So we also evaluated readability (does it still sound like a human wrote it?) and meaning preservation (did GPTinf keep the original arguments intact, or did it drift into nonsense?).

We ran the test three times and averaged the results to account for any randomness in the output. No cherry-picking, no best-case scenarios. Just the numbers.

The Perkins et al. (2024) study used a similar approach — testing 114 text samples across 7 AI detectors and finding that simple adversarial techniques reduced detector accuracy by 17.4% on average. We wanted to see where GPTinf landed on that spectrum: does it push past that average, or does it fall short?

Here's where it gets rough. GPTinf didn't bomb on every detector, but it didn't ace anything either. The results were wildly inconsistent, which is honestly the worst outcome for a tool you're supposed to trust with important submissions.

Some detectors got fooled. ZeroGPT dropped to 28% AI, which counts as a pass. Copyleaks and GPTZero came down to the mid-30s — not bad, but still flagged as partially AI-generated by most standards. But here's where it falls apart: Originality.ai barely budged. Going from 99% to 55% sounds like progress until you realize that anything above 50% is still a hard fail. And Turnitin at 42% is a real problem for students: most universities flag anything above 20%.

But our test results were actually *generous* compared to what other independent testers found. Originality.ai's own review team ran GPTinf output through their detector and got 100% AI confidence — completely unchanged from the original. GPTZero flagged it at 100% AI. Copyleaks: 100% AI. A separate test by Grubby.ai found GPTZero still flagging GPTinf output at 81% probability of being AI-generated. In the most damning independent review, GPTinf's output was indistinguishable from the raw AI text across all four detectors tested.

GPTinf claims a 96-99% success rate on their website. The independent data does not support that claim. Not even close.

The pattern across all tests is clear: GPTinf handles the least sophisticated detectors (see how AI detectors work) (ZeroGPT, which has a real accuracy of only 35-65% according to independent testing) but collapses against the tools that actually matter — Turnitin, Originality.ai, and GPTZero.

GPTinf's pricing is more complex than it first appears, and it's significantly more expensive than many people realize.

The free tier gives you roughly 3,000 words total — not per month, total — with a 300-word limit per process. That's enough for maybe two short paragraphs before you're done forever. Unlike most competitors, this isn't a recurring monthly allowance. Once you use it, it's gone.

Paid plans start at the Lite tier: $9.99/month for 20,000 words per month with a 500-word cap per process. That 500-word limit is brutal for anyone processing full essays or articles — you'd need to split a 2,000-word paper into four separate runs. The Pro plan at $24.99/month bumps you to 50,000 words with unlimited words per process.

Here's where it stings: credits expire monthly and don't roll over. If you buy 20,000 words and only use 5,000, those remaining 15,000 vanish. Multiple reviewers flag this as a significant drawback, especially for students who might need a humanizer heavily during finals week and barely at all the rest of the month.

The refund policy is equally restrictive: you only qualify for a refund if you've used fewer than 500 words in your billing period. Above that? You're locked in. One Trustpilot reviewer (December 2025) reported paying for an annual subscription but only receiving one month of word credits, with three support emails yielding a single template response.

For context, here's what other tools charge for better performance:

We're not here to trash GPTinf. It's a real tool that does real work — it just has serious limitations you should know about before handing over your credit card. GPTinf holds a 3.6 out of 5 on Trustpilot, which reviewers characterize as "Average." The positive reviews praise the simple interface and fast processing. The negative reviews paint a different picture: poor bypass performance, grammar errors in output ("in future" instead of "in the future," "usher-in" instead of "usher in"), clunky phrasing, and a customer support team that responds with templates when they respond at all.

Look, GPTinf isn't a scam. It does *something*. But when you compare the numbers side by side, the gap is hard to ignore.

UndetectedGPT achieved a 96% bypass rate across the same five detectors where GPTinf averaged around 60% in our tests — and performed even worse in independent reviews. On Turnitin specifically, UndetectedGPT scored under 5% AI compared to GPTinf's 42%. On Originality.ai — the detector GPTinf essentially failed against — UndetectedGPT came in under 4%. That's not a marginal difference. That's the difference between passing and failing.

But here's where it gets really damning: the readability gap might matter even more than the bypass numbers. GPTinf's output requires editing. Independent reviewers document grammar errors, clunky substitutions, and phrasing that makes a teacher pause even without running a detector. The Weber-Wulff et al. (2023) study found that all 14 AI detection tools scored below 80% accuracy, which means detectors aren't infallible. But they don't need to be infallible when your humanized text already sounds robotic to a human reader.

UndetectedGPT's output reads naturally. Sentence lengths vary, word choices feel deliberate, and your original meaning stays intact. At $19.99/month, it costs more than GPTinf's $9.99/month Lite plan, but the results aren't even in the same league: 96% bypass versus roughly 45% in independent testing. You're paying more, but the performance gap is enormous.

The Liang et al. (2023) Stanford study found that AI detectors flag 61.3% of non-native English essays as AI-generated. If you're an ESL student already fighting an uphill battle against biased detectors, you need a tool that actually works — not one that leaves you at 42% on Turnitin and hoping your professor doesn't notice.

If you're currently using GPTinf and getting flagged, run a free test on UndetectedGPT. You'll see the difference in 30 seconds.