Grubby AI Review (2026): Great Writing, But Its GPTZero Mode Failed GPTZero

Grubby AI writes clean, faithful rewrites, but it didn't get past AI detectors in our test. In September 2026, the HumanizerPRO team ran a GPT-4o sample through Grubby's default GPTZero mode. GPTZero and Sapling both rated the result 100% AI, and ZeroGPT rated it 36% AI. Without an account you only get a two-sentence preview, and a free account gives you 300 words a month. Paid plans start at $6.99 a month billed yearly, and monthly plans are billed every four weeks. We rate it 4 out of 10. HumanizerPRO and SuperHumanizer scored far lower on ZeroGPT and Sapling with the same text.

Grubby AI at a glance

What is Grubby AI?

Grubby AI, at grubby.ai, is an AI humanizer from Study Solutions A16 LLC, which says more than 1.6 million students have used it. You paste in AI-generated text and choose a mode (the default is GPTZero; the others are ZeroGPT and Academic (Turnitin)), and Grubby rewrites it so it reads as human and can pass an AI detection check.

Grubby supports English only and has an editor that takes up to 5,000 words, but each plan limits how many words you can humanize per input. Paid plans also come with an "AutoTyper" allowance of 5,000 to 20,000 words a month, depending on the plan.

How we tested Grubby AI

Grubby's free account includes 300 words a month, which is less than the 306-word GPT-4o sample we usually use. So in September 2026, the HumanizerPRO team used our shorter, 190-word version of the same text: a post about a new blood test that estimates biological age. A team member created a free Grubby account, pasted the text, left the mode on the default "GPTZero" setting and humanized it.

We ran the output through GPTZero, ZeroGPT and Sapling and compared it with the original, line by line. To make the comparison fair, we put the exact same 190-word text through HumanizerPRO and SuperHumanizer and checked those outputs on the same three detectors.

What you get without an account

At first, Grubby looks free: there's no account needed, so you paste your text, hit Humanize and watch a timer count down. But only the first paragraph of the output is a genuine rewrite, and it's only about two sentences long. From there on, the original text's words are shuffled into gibberish ("A poorly—the body's or monitor those the could test By systems a"), hidden behind a "Subscribe to Unlock" button.

So you can't properly judge the output without an account, and even then you only get 300 words a month.

Does Grubby AI bypass AI detectors?

Not in our test. Even though we used the mode named after GPTZero, GPTZero was "highly confident this text was AI generated" and rated it 100% AI and 0% human. Sapling also rated the text 100% AI. ZeroGPT rated it 36% AI and called it "most likely human written", but said it may contain AI-generated parts.

To be fair to Grubby, GPTZero is currently strict. In our September 27 checks, it also rated the HumanizerPRO and SuperHumanizer outputs for the same text 100% AI. The difference showed up on the other two detectors.

On Sapling, Grubby's output scored 100% AI, while SuperHumanizer's scored 2.5% and HumanizerPRO's 0%. On ZeroGPT, Grubby scored 36% AI, against 11.6% for SuperHumanizer and 0% for HumanizerPRO. For why detectors disagree this much, see are AI detectors accurate?

How good is Grubby AI's writing?

This is where Grubby shone. The rewrite was clear and easy to read. It kept every important detail: the test reads hundreds of proteins, it can reveal problems "prior to clinical signs", doctors could personalize prevention and treatment, and people can monitor how exercise and diet affect their biological age. It kept the original's two-paragraph structure and didn't add any new claims.

The only questionable spot was a loose sentence at the end: "Even as we age, healthspan could be extended using this technology." Otherwise, it read as if a person had edited it carefully by hand. The real problem is that neat, careful editing like this still looks AI-generated to GPTZero and Sapling.

Grubby AI's claims, checked

Grubby's website makes several bold claims. Here's how they hold up:

• "ChatGPT embeds watermarks in its text." OpenAI has said it built a text watermarking method but hasn't released it in ChatGPT. There's no public evidence of hidden watermarks in ChatGPT's text for a humanizer to remove.
• "Grubby is the only humanizer that guarantees" a Turnitin bypass, with money back if detected. StealthGPT also offers a "Detected? Get your money back" guarantee (see our StealthGPT review). Grubby's guarantee applies to paid plans.
• "99.8% bypass rate" in Academic mode. This is Grubby's own figure. We couldn't check it, because Turnitin is only available through schools. Since August 2025, Turnitin also flags text it thinks was rewritten by AI humanizers.

Grubby AI pricing and plans

The yearly prices are fair. Be careful with the monthly plans, though: they're billed every four weeks rather than every calendar month, so you pay 13 times a year. On Essential, that's about $195 a year instead of $180. Essential also includes only Grubby's "Simple" mode and 500 words per input; the Standard and Enhanced modes start with Pro.

In contrast, HumanizerPRO lets you humanize 500 words without an account, and its plans start at $7 a month billed yearly, with up to 3,000 words per input and a 3-day money-back guarantee.

Grubby AI pros and cons

What's good

• Clear, accurate rewrites that kept every key fact in our test
• Yearly plans are reasonably priced
• Large 5,000-word editor and up to 2,500 words per input on higher plans
• Money-back guarantee if Turnitin flags your text (paid plans)

Downsides

• Its GPTZero mode output scored 100% AI on GPTZero and Sapling
• No real free result without an account, and only 300 words a month with one
• English only
• Monthly plans are billed every four weeks, so you pay 13 times a year
• Misleading claims, including that ChatGPT embeds watermarks in its text

Grubby AI vs. SuperHumanizer vs. HumanizerPRO

GPTZero flagged all three outputs in our test, so none of them is a sure way past GPTZero right now. On ZeroGPT and Sapling, both SuperHumanizer, our sister tool, and HumanizerPRO did much better than Grubby. SuperHumanizer is free with no sign-up, and HumanizerPRO lets you check your own result with its free AI detector before you submit anything.

Is Grubby AI worth it?

Grubby AI is worth considering if clean, accurate writing is your priority and you don't mind paying yearly. Its rewrite was one of the most faithful of any tool we've tested.

But if your goal is getting past AI detectors, our test doesn't support its promises. Its GPTZero mode didn't pass GPTZero, and Sapling rated its output 100% AI. Before paying, try SuperHumanizer for free or HumanizerPRO without an account, and check the results yourself. For more options, see our ranking of the best AI humanizers.

Frequently asked questions

Is Grubby AI free?

Only in a limited way. Without an account, Grubby shows a two-sentence preview and blurs the rest. A free account includes 300 words a month. Paid plans start at $6.99 a month billed yearly. SuperHumanizer is a completely free alternative with no sign-up and 1,200 words per run.

Does Grubby AI bypass GPTZero?

Not in our test. We used Grubby's GPTZero mode, and GPTZero rated the output 100% AI. Sapling also rated it 100% AI, and ZeroGPT 36% AI.

Does Grubby AI bypass Turnitin?

Grubby claims a 99.8% Turnitin bypass rate in Academic mode and offers a money-back guarantee on paid plans. We had no way to confirm this, because Turnitin is only available through schools. Also, since August 2025, Turnitin flags text it suspects was changed by AI humanizers.

Does ChatGPT put watermarks in its text?

Not that anyone has shown. OpenAI has said it developed a text watermarking method but hasn't released it in ChatGPT. Grubby's claim that it removes "ChatGPT watermarks" isn't backed by public evidence.

What languages does Grubby AI support?

English only, according to Grubby's own FAQ. HumanizerPRO works in 8 site languages, and its API supports 30+.

What is the best Grubby AI alternative?

SuperHumanizer is the best free alternative: it's free, needs no sign-up and scored 11.6% AI on ZeroGPT and 2.5% on Sapling in our test. HumanizerPRO is the best paid alternative: it scored 0% AI on both, lets you try 500 words without an account, and costs from $7 a month billed yearly.