Here's the thing: QuillBot was never designed to beat AI detectors. It's a paraphrasing tool, built to help you reword sentences — not to fool detection algorithms. For a while, that distinction didn't matter. Back in 2024, AI detectors were still pretty basic. Swapping a few synonyms and rearranging sentence structure was enough to slip past most of them.

But detectors got smart. Fast.

Turnitin's July 2024 update was the big one: they launched a dedicated AI paraphrasing detection feature that specifically identifies where a "text spinner" was applied to AI-generated writing. It doesn't just flag AI text anymore — it shows a separate breakdown of text that was likely AI-generated *and then paraphrased*. GPTZero and Originality.ai followed with similar updates within months.

Then Turnitin dropped the hammer again in August 2025: dedicated AI bypasser and humanizer detection, specifically trained to catch text processed by humanizer and bypasser tools. QuillBot went from "good enough" to outclassed in two updates.

The problem runs deeper than just detector updates. AI detectors don't look at individual words anymore. They analyze writing patterns across entire documents: sentence length distribution, transition predictability, vocabulary clustering. QuillBot changes the surface. It swaps words. It flips clauses around. But the underlying statistical fingerprint of AI-generated text stays intact.

We ran a GPT-5 essay through QuillBot's strongest mode and tested it against five detectors. Originality.ai still flagged the output at 96% AI. GPTZero flagged it at 100% AI. Even QuillBot's own built-in AI detector flagged the paraphrased text as 100% AI. The only detectors it fooled were ZeroGPT (which has a real accuracy of only 35-65% according to independent testing) and Writer. Against anything serious? QuillBot changes the surface appearance without altering the underlying signals that detectors are actually trained to catch.

Yes. And Turnitin has explicitly said so. This isn't speculation or inference — Turnitin's own documentation states their AI detection can identify text that was "likely AI-generated and then likely modified by an AI-paraphrasing tool or AI word spinner, such as QuillBot." They named QuillBot by name.

Here's the timeline of how Turnitin systematically closed the paraphrasing loophole:

April 2023: Turnitin launches AI writing detection. At this point, basic paraphrasing through QuillBot could sometimes slip through.

July 16, 2024: Turnitin launches dedicated AI paraphrasing detection. This feature doesn't just flag AI text — it creates a separate category showing where a text spinner was applied to AI writing. Reports now show a breakdown: percentage likely AI-generated vs. percentage likely AI-generated *and then AI-paraphrased*. This update was integrated into existing AI detection with no settings changes required.

August 27, 2025: Turnitin launches AI bypasser/humanizer detection, targeting text modified by dedicated AI humanizer and bypasser services. Available in English only, trained specifically against "leading bypassers."

So in 2026, Turnitin has three layers of detection: raw AI text, paraphrased AI text, and humanized AI text. QuillBot gets caught by the second layer. The question isn't whether Turnitin can detect QuillBot — it's whether Turnitin has gotten so good that even dedicated humanizers are at risk.

The Perkins et al. (2024) study found that paraphrasing specifically reduced detector accuracy by about 21% — not enough. That means roughly 4 out of 5 paraphrased texts still get caught. The Weber-Wulff et al. (2023) study found that over 50% of paraphrased AI texts went undetected by some tools, but Turnitin was the exception — it was the only tool that correctly classified all documents in certain pure-AI categories.

Bottom line: if your school uses Turnitin (and there's an 80% chance it does), QuillBot is not going to save you. You need something that operates at a fundamentally different level.

This is the distinction that most people miss, and it's the entire reason QuillBot fails at beating detectors while dedicated humanizers succeed.

A paraphraser like QuillBot works at the word and sentence level. It takes your input and rewrites it using different vocabulary and slightly different structures. The meaning stays roughly the same, the words change. Think of it like putting a new coat of paint on a house — the house is still the same shape. AI detectors don't care about the paint. They care about the shape.

A humanizer works at the pattern level (learn more in our paraphraser vs humanizer breakdown). Instead of just swapping words, it restructures how the text *behaves* statistically. It adjusts perplexity (how predictable the word choices are) and burstiness (how much sentence length and complexity varies). These are the exact metrics AI detectors measure. A good humanizer makes AI text exhibit the same chaotic, inconsistent patterns that real human writing has: the sudden short sentence after a long one. The slightly unusual word choice that a thesaurus wouldn't suggest. The natural rhythm that comes from actually thinking while you write.

The research backs this up completely. The Perkins et al. (2024) study tested adversarial techniques against 7 AI detectors across 805 interactions and found that while basic paraphrasing reduced accuracy by about 21%, dedicated humanization was the most effective adversarial approach — reducing accuracy far more dramatically. The Weber-Wulff et al. (2023) study tested 14 detection tools and found that "none of the tools could correctly classify all AI-generated documents that undergo manual editing or machine paraphrasing" — but over 50% of paraphrased texts still got caught. Paraphrasing helps. It's just not enough.

That's why you can run the same essay through QuillBot ten times and still get flagged at 96% AI on Originality.ai, but a single pass through a quality humanizer drops the score to under 5%. They're solving fundamentally different problems. QuillBot rewrites sentences. A humanizer rewrites the math underneath them.

The numbers tell a clear story. Every dedicated AI humanizer on this list outperforms Wordtune, which — like QuillBot — is fundamentally a rewriting tool rather than a detection bypass tool. Wordtune's 45% bypass rate is actually *worse* than what we got from QuillBot's strongest mode. It costs $13.99/month (or $6.99/month annual) for its Advanced plan. Fine tool for improving your writing. Completely wrong tool if your goal is beating AI detectors.

The humanizers, on the other hand, all clear 78% or higher. That's because they're purpose-built for this exact task. They understand what detectors look for and they specifically target those signals.

UndetectedGPT leads the pack at 96%, which in practical terms means it fools virtually every detector virtually every time. Undetectable AI comes in second at 88% but costs $19/month for 8 points less performance. StealthGPT costs $32/month at 82%, but independent testing shows wildly inconsistent results (Originality.ai flagged StealthGPT output at 100% AI in multiple reviews).

Here's the key comparison people miss: QuillBot Premium costs $19.95/month ($8.33/month on annual billing). UndetectedGPT costs $19.99/month, comparable price, but it actually works. You'd be paying the same for QuillBot to get results that *don't work* as you'd pay for the tool that does. And UndetectedGPT offers a free tier so you can test it before committing.

For reference, QuillBot's free tier limits you to 125 words per paraphrase. That's about two sentences. The premium modes (Fluency, Formal, Simple, Creative, Expand, Shorten, Custom) are locked behind the paywall. Even with all seven modes unlocked, the fundamental problem remains: paraphrasing doesn't change the statistical patterns that detectors measure.

After testing every serious QuillBot alternative against the same five detectors, UndetectedGPT came out so far ahead it almost felt unfair. A 96% bypass rate means it consistently fooled Turnitin, GPTZero, Originality.ai, Copyleaks, and ZeroGPT — not just the easy ones.

But here's what really matters if you're switching from QuillBot: the output quality. A lot of humanizers produce text that passes detection but reads like something got lost in translation. You fix the detection problem but create a readability problem. UndetectedGPT's output actually sounds like a person wrote it. The sentence rhythm feels natural. The word choices make sense. Your arguments stay intact — it's not scrambling your ideas to dodge an algorithm.

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 or writer, you're fighting a system that's biased against your writing style before you even start. A tool like UndetectedGPT doesn't just bypass detection — it restructures the statistical patterns so your text reads like confident, natural English. That matters for human readers too, not just algorithms.

If you're coming from QuillBot, you'll notice the workflow is almost identical. Paste your text, click a button, get results. Except this time the results actually work. At $19.99/month (with a free tier to test first), it's comparable in price to QuillBot Premium ($19.95/month), but the results aren't even in the same universe. You get multiple humanization modes so you can adjust intensity based on what you're submitting and where. Need to beat Turnitin on an academic paper? Crank it up. Just cleaning up a blog post? Use the lighter touch. That flexibility matters when you're dealing with different detectors in different contexts.

If you've been using QuillBot as part of your writing workflow, switching to a humanizer is easier than you might think. The process is almost identical: you're still pasting text into a tool and getting a rewritten version back. The difference is what happens behind the scenes — and what happens when your professor runs it through Turnitin.

Start by testing your current workflow: take something you'd normally run through QuillBot, process it through UndetectedGPT instead, and check the output against GPTZero or ZeroGPT (both offer free checks). You'll see the difference immediately. Text that QuillBot leaves at 96% AI on Originality.ai will drop below 5%.

One critical thing to avoid: stop stacking tools. We see a lot of people who run text through QuillBot *and then* through a humanizer, thinking double processing means double protection. It doesn't. In fact, research on adversarial paraphrasing found that simple sequential paraphrasing can actually increase detection rates on some detectors. The QuillBot pass introduces its own detectable patterns — uniform synonym distribution, predictable restructuring — that the humanizer then has to work around. It's like putting on a disguise and then a second disguise on top: it doesn't make you less recognizable, it just makes you look weird.

Just go straight from your AI-generated draft to the humanizer. One pass. That's it. The Perkins et al. (2024) study tested 114 text samples across 7 detectors and found that the most effective techniques were single, well-optimized transformations — not sequential stacking. If you're using UndetectedGPT, experiment with the different humanization modes to find the right balance between maximum stealth and keeping your original voice. Most people find the default mode handles 90% of use cases perfectly.

Also: read the output before submitting. This applies to any tool, not just humanizers. Even at a 96% bypass rate, a 30-second read-through catches the occasional odd phrasing and lets you add personal touches that make the text genuinely yours. The combination of humanization plus a quick manual edit is dramatically more effective than either alone.