Undetectable AI is an AI humanization platform that transforms AI-generated text into content designed to bypass AI detection tools. It launched in May 2023, co-founded by Christian Perry, Bars Juhasz (a PhD student from Loughborough University), and Devan Leos. The company grew fast: 100,000 waitlist signups before launch, 2 million users within the first six months, and over 11 million users as of late 2024.

The tool supports multiple writing modes: University, High School, Journalist, Marketing, Essay, Story, Business, and General. It claims to bypass all major detectors including Turnitin, GPTZero, Originality.ai, Copyleaks, and ZeroGPT. One of its standout features is a built-in AI detection checker that lets you scan up to 10,000 words for free without signing up, showing how your text performs against multiple detectors simultaneously.

Undetectable AI also offers a Chrome extension, Zapier integration (connecting to Google Sheets, RSS feeds, and email workflows), an embeddable widget for WordPress and other platforms, and API access for developers. It supports over 50 languages, though English produces the most accurate results.

With 11 million users, it's the biggest name in the humanizer space. But popularity doesn't always equal performance. So we tested it ourselves.

Undetectable AI uses natural language processing to analyze and restructure AI-generated text. The process works in stages:

1. Pattern analysis. The tool identifies AI-typical patterns in your text: uniform sentence lengths, predictable word choices, formulaic paragraph structures, and the low perplexity and burstiness scores that detectors flag.

2. Sentence restructuring. It varies sentence length, structure, and complexity to break the metronomic rhythm of AI writing. Short sentences get followed by longer ones. Passive constructions mix with active ones.

3. Vocabulary adjustment. Predictable word choices get replaced with more varied alternatives. This goes beyond simple synonym swapping: the tool aims to change the overall vocabulary distribution to match human writing patterns.

4. Tone calibration. Based on your selected writing mode (University, Journalist, Marketing, etc.), the output gets adjusted to match the expected tone and formality level.

The interface is straightforward: paste text, select a style and readability level, click humanize. Results appear in about 10-30 seconds depending on length. There's a word limit per request of 2,000 words on the standard plan and 3,500 words on Premium Pro.

One useful feature: after humanization, Undetectable AI runs the output through its built-in multi-detector checker so you can see the estimated scores before copying the text. That saves you the step of manually checking against separate detector sites.

Undetectable AI's pricing has shifted since launch. Here's the current breakdown:

Free trial: 250 words over 3 days. No credit card required. Barely enough to test one paragraph.

Monthly plan: Starting at $19/month for 10,000 words, scaling up to $199.50/month for 1,000,000 words.

7-day money-back guarantee on all paid plans. But here's a catch that shows up in user complaints: if you cancel before your billing period ends, remaining credits are forfeited immediately. No prorating.

Payment methods include Visa, MasterCard, American Express, and PayPal. Enterprise plans offer bank transfers.

For comparison: - UndetectedGPT: $19.99/month (free plan available) - StealthGPT: $32/month - WriteHuman: $18/month - HIX Bypass: $19.99/month

At $19/month for 10,000 words, Undetectable AI sits in the same price range as UndetectedGPT ($19.99/month), but delivers a lower bypass rate (88% vs 96%). The free trial is too limited for a meaningful test.

We tested Undetectable AI using the same methodology we apply to every tool: a 1,000-word GPT-5 generated essay run through the tool, then checked against 7 detectors. We ran three tests and averaged the results.

The original essay scored 95-99% AI across all detectors. Here's what happened after Undetectable AI processed it:

The numbers above tell part of the story. Here's what they don't show.

The Turnitin problem. Undetectable AI brought our test essay from 98% to 18% on Turnitin. That sounds great until you realize many institutions use a 20% threshold for flagging (see our Turnitin AI detection guide). At 18%, you're technically below that line, but barely. One slightly different essay or a different Turnitin scan could push you over. UndetectedGPT's 4% gives you a much wider safety margin. When the consequence of getting flagged is an academic integrity investigation, margins matter.

Readability inconsistency. On our test essay, the output was solid. But when we tested with more complex, technical content (a research methods discussion with statistical terminology), the quality dropped. Sentence structures became awkward, and some domain-specific phrasing was mangled. Multiple user reviews on Trustpilot and Reddit report similar issues: the tool sometimes produces "disjointed" text that requires significant manual cleanup.

Meaning drift on longer texts. For shorter pieces (under 500 words), meaning preservation was good. For longer pieces, we noticed the tool occasionally rephrased arguments in ways that subtly changed the point being made. Not drastically, but enough that you'd need to re-read carefully and correct.

Trustpilot tells a story. Undetectable AI has a 2.1 out of 5 stars on Trustpilot across 762 reviews. Common complaints include: inconsistent bypass effectiveness, grammar mistakes and awkward phrasing in output, billing issues (users charged after canceling), and the 250-word free trial being too limited for meaningful testing. Some users report excellent results; others say it "makes writing sound robotic." That inconsistency is the concern.

GPTZero has adapted. GPTZero has incorporated paraphrasing detection specifically to flag tools like Undetectable AI. Some independent tests have shown Undetectable AI scoring under 40% on humanization benchmarks where competitors achieved 80-90%. The detection arms race is real, and being the biggest target means detectors are specifically training against your output.

Here's our honest assessment after extensive testing:

Since these are the two most compared tools in the space, here's the direct comparison based on our testing.

Bypass rate: UndetectedGPT averaged 96% across all detectors. Undetectable AI averaged 88%. The 8-point gap shows up most clearly on Turnitin (4% vs 18%) and GPTZero (6% vs 22%). Both passed Copyleaks and ZeroGPT reliably.

Turnitin specifically: This is where the gap matters most. UndetectedGPT's 4% score gives you a wide safety margin below Turnitin's 20% threshold. Undetectable AI's 18% puts you right at the edge. If you're a student and Turnitin is what your school uses, that difference is the difference between sleeping well and checking your email every five minutes.

Readability: UndetectedGPT scored 9.2/10 in our testing. Undetectable AI scored 8.5/10. Both produce natural-sounding output on standard content, but UndetectedGPT maintained quality better on technical and complex texts.

Meaning preservation: Both tools preserve meaning well on shorter texts. On longer content (1,000+ words), Undetectable AI showed more meaning drift requiring manual correction. UndetectedGPT was more consistent at preserving the original argument structure.

Pricing: UndetectedGPT starts at $19.99/month (Starter plan), with a free plan available to test results first. Undetectable AI starts at $19/month for 10,000 words. At nearly the same price, UndetectedGPT delivers the highest bypass rate in testing (96% vs 88%) and the best readability (9.2/10 vs 8.5/10). You're paying the same but getting better results.

User satisfaction: Undetectable AI has a 2.1/5 on Trustpilot with complaints about inconsistent results and billing. UndetectedGPT doesn't have the same scale of negative feedback.

The verdict: Undetectable AI is a legitimate tool with a massive user base, and it works. But UndetectedGPT outperforms it on every metric that matters: bypass rate, readability, meaning preservation, and month-to-month pricing. If you're choosing between the two, the data points one direction.

Undetectable AI is a competent tool. It works, it has a proven track record with 11 million users, and it's better than most budget alternatives. The built-in multi-detector checker, multiple writing modes, Chrome extension, and 50+ language support show a mature platform that's invested in features.

But in 2026, it's no longer the clear market leader for performance. Our testing showed it achieving an 88% bypass rate, which is solid but falls short of the 96% we measured with UndetectedGPT. The Turnitin scores are the most concerning: 18% puts you too close to the 20% flagline for comfort. The Trustpilot reviews (2.1/5) and reports of GPTZero specifically adapting to detect its output add caution.

If you're already paying for Undetectable AI annually and satisfied with the results, there's no urgent reason to switch. But if you're choosing a humanizer for the first time, or if you need higher reliability (especially against Turnitin), or if you want better value on a monthly plan, UndetectedGPT offers the highest bypass rate in testing (96%) and best readability (9.2/10), with a free plan so you can verify results before committing. The data doesn't lie.