SupWriter vs Undetectable AI: Head-to-Head Comparison (2026)

Undetectable AI is one of the most recognized names in the humanizer market. SupWriter is ours. Here is how they compare on the things you can actually check: price, limits, tooling, languages, and how each one's output should be judged.

Let's get the bias out of the way first: we built SupWriter, so read everything below with appropriate skepticism. What we can promise is that every price and limit here comes from each company's own pages (Undetectable AI's were checked in September 2026), and that we have not run a controlled bypass test on either tool, so we are not going to quote one. There are places where Undetectable AI genuinely beats us, and we say so in plain language.

If you only have thirty seconds: Undetectable AI gives you more words per dollar, a broader content suite, and a bigger brand. SupWriter gives you a no-card free tier, a detector with sentence highlights in the same editor as grammar and paraphrase tools, and developer options (an API, an MCP server and a CLI). Neither tool can promise how a specific detector will score your text. Which of those matters more depends entirely on what you are submitting and where.

Quick Verdict

Undetectable AI figures come from its pricing page and homepage, checked Sept 2026. SupWriter figures are our list prices; student, regional and promo discounts exist.

A note on why there is no bypass-rate row, since a missing row in a comparison table usually means somebody is hiding something. A bypass rate is only meaningful when it names the detector, the date, the sample set and the scoring rule, and we have not published a test like that for either tool. Undetectable AI's pricing page promises that its output "passes AI detectors"; we would rather you check both tools against the detector you will actually face.

Bypass Rates, Detector by Detector

The honest version of this section is short: neither company publishes a controlled, per-detector test you could audit, so there are no per-detector numbers to compare.

What is documented is how the detector side has moved. Turnitin added detection of text that "may have been intentionally modified by AI humanizer tools" on 27 August 2025, for English submissions only (Turnitin). In July 2026 it consolidated its detection models into a single model, and it says the AI percentage "should not be used as the sole basis for action" (Turnitin AI detection FAQ). In other words, Turnitin is explicitly looking for humanizer output, from us, from Undetectable AI, and from everyone else. If you want the background, we covered the feature in our Turnitin bypasser detection analysis.

One more honest caveat that applies to both tools: no humanizer is at 100%, and any vendor claiming certainty is selling you something it cannot deliver. SupWriter rewrites AI-assisted drafts so they read naturally, and you can check the result with the built-in AI detector before you submit. That detector is a pre-check based on one scoring model, not Turnitin or GPTZero, and results vary by detector, text length and topic. That is not a sales pitch, it is just basic hygiene.

Academic Register: The Metric Nobody Markets

Bypass claims are what every humanizer puts on its homepage. Whether the output still sounds like academic writing is what decides whether it is usable.

We have not run a blind reader panel on either tool, so we are not going to score them. What we can tell you is what to look for when you read the output, because the failure modes are consistent across the category: hedged claims hardening into absolute ones, technical terms getting swapped for near-synonyms that are not actually synonyms in that field, and restructured sentences that change which clause is doing the work. In a marketing blog post, none of that matters much. In a literature review where "suggests a correlation" becomes "demonstrates," it matters a great deal.

References deserve their own check. Count the citations in your input, then count the ones that come back intact, with the same authors, years, and page numbers. Anything a rewrite touched inside a reference is something you will repair by hand.

Formatting is the last thing to check. Run a document with bold text, headers, bullets and links through each trial, and see what survives. If you are humanizing structured documents, budget time for putting the structure back.

Before and After: Two Rewrite Styles to Watch For

Numbers are abstract. Here is a paragraph of standard ChatGPT academic filler, followed by two rewrites we wrote ourselves to illustrate the two styles you will see from humanizers. They are illustrations, not captured output from either product. Run the same paragraph through both trials and compare.

The original AI text:

Remote work has fundamentally transformed the modern workplace in numerous significant ways. Studies suggest that employees who work remotely may experience increased productivity, although results vary considerably across industries and roles. Organizations must therefore carefully consider a variety of factors when implementing remote work policies.

A synonym-inflation rewrite:

Remote employment has thoroughly reshaped the contemporary workplace across many meaningful dimensions. Research demonstrates that staff members working remotely experience heightened productivity, though outcomes differ substantially between sectors and positions. Companies should therefore thoughtfully weigh numerous considerations while establishing remote work policies.

A structural rewrite:

Remote work has changed the workplace, and not in one tidy direction. Some studies find remote employees get more done. Others find the opposite, and the split usually tracks with the industry and the specific role rather than with remote work itself. So policy decisions have to start from what the job actually involves.

Look at what happened to the hedge in the second sentence. The original said studies "suggest" that productivity "may" increase. The inflated rewrite says research "demonstrates" that staff "experience" heightened productivity. That is a real claim strengthening, and in an assessed paper it is the kind of thing that gets a comment in the margin.

The inflated version is also doing something readers notice: register inflation. Work becomes employment, modern becomes contemporary, many becomes numerous. Every word gets one notch fancier while the sentence rhythm stays identical. Human writers do not upgrade every noun at once, and they do not write three sentences of matching length in a row. Whichever tool you try, that is the pattern to watch for in its output.

Languages: What Each Tool Supports

Undetectable AI says its tools support 50+ languages, "with English offering the highest accuracy" (homepage). SupWriter's editor supports 50+ languages. Beyond those claims, the best evidence is your own: run a paragraph in your language through both trials and have a native speaker read the results for grammar, case endings, and whether the text reads as if it took a detour through English.

The detector side matters here too. Turnitin's AI writing detection covers long-form English, Spanish, Japanese and Modern Arabic only, and its humanizer and paraphrase detection is English-only (Turnitin AI detection FAQ). GPTZero says it fully supports English, German, Portuguese, French and Spanish (GPTZero). Detection in other languages is thinner, and less reliable when it does exist.

That includes our own detector. When we checked it on non-English drafts in September 2026, it scored some fully AI-written drafts well short of 100% AI and returned 0 for both the AI draft and the rewrite in several languages. For most non-English languages, treat any detector score, ours included, as a weak signal.

Our full writeup on this is in AI humanizer for non-English content, including why detectors themselves misfire on non-English text in the first place.

Speed

Neither company publishes a speed benchmark, and we have not timed the two under controlled conditions, so we are not going to quote seconds.

Is speed the deciding factor? Almost never. But if you are iterating (humanize, check, adjust tone, humanize again), the length of that loop changes how many passes you are willing to try before a deadline. The trials will tell you quickly whether either one feels slow on your kind of document.

Pricing and Free Tiers

Undetectable AI's pricing has moved around, so check their page before you commit. As of September 2026, the Starter tier is $9.99/month for 10,000 words, Professional is $19.00 for 20,000 words, and Advanced is $31.00 for 35,000 words. Annual billing roughly halves those: $5.00, $9.50 and $15.75 a month (pricing page).

SupWriter's list prices are $9.99/month for 5,000 words (Basic), $19.99 for 15,000 (Pro) and $39.99 for 30,000 (Ultra). Annual billing is $4.99, $9.99 and $19.99 a month, with 12 months of credits upfront, and you can buy extra credits if you run out.

Here is the fair version of the comparison, because identical $9.99 sticker prices hide a real difference. Per 1,000 words, Undetectable AI's Starter plan works out to about $1.00 on monthly billing and $0.50 on annual billing. SupWriter's Basic plan is $2.00 monthly and $1.00 annual, and Pro and Ultra are $1.33 monthly and $0.67 annual. At list price, Undetectable AI is cheaper per word at every tier we compared.

What price per word does not capture: how much text you can send at once (SupWriter's Basic plan caps a single request at 500 words), what else is bundled, and whether you will need a second pass, which depends on your text and your detector rather than on anyone's marketing. Our AI humanizer pricing comparison works through the per-word math across more tools.

On free tiers: Undetectable AI offers a 250-word trial. SupWriter's free humanizer gives you 300 words with no credit card, though you need an account. Both are enough to form an opinion, which is more than several competitors offer.

Where Undetectable AI Genuinely Wins

We are not going to pretend this is a one-sided product.

Price per word. As the math above shows, Undetectable AI gives you more words for the money at every tier we compared.

Breadth of tooling. Undetectable AI is a suite, not a single tool: an AI essay writer, an SEO content writer, a paraphraser, a job applier, and image and audio detectors sit alongside the humanizer (homepage). Its paid tiers also list API compatibility and unlimited AI detecting on every plan (pricing page), while SupWriter reserves API keys for Pro and Ultra. If you want one subscription covering generation and humanization, that consolidation is worth real money.

Human Auto Typer. This is the feature nobody else in this comparison ships. It is a Chrome extension that types pre-written text into Google Docs and other editors "exactly how a human would," with pauses and errors, and it is included for subscribers (Undetectable AI). Be clear-eyed about what that means in a classroom: if your instructor reads version history as evidence of how you wrote something, a simulated typing session is not your writing process, and presenting it as one can be an integrity problem in its own right.

Brand and scale. Undetectable AI says it is "trusted by 24M+ users" (homepage). If you are buying tooling for a team and need to justify the vendor to someone else, name recognition is a legitimate factor, not a vanity one.

Marketing content. For blog posts, social copy, and product descriptions where a flag costs you nothing, the extra words per dollar matter more than anything else in this comparison.

Who Should Pick Which

Pick SupWriter if: you want to try before paying without handing over a card, you want the humanizer, detector, grammar checker and paraphraser in one editor, you write in more than one language and want them in the same place, or you want to connect it to your own tools through the API, MCP server or CLI.

Pick Undetectable AI if: you want the most words per dollar, you want the whole content pipeline in one subscription, you need API access on an entry-level plan, or you are producing low-stakes marketing content.

If you are weighing other options too, our roundups of the best AI humanizer tools and best AI humanizer for academic papers cover the wider field, and we keep a dedicated Undetectable AI alternative page.

Just Run the Test Yourself

Honestly, this is the part we would push hardest. Generate a paragraph with ChatGPT. Run it through Undetectable AI's trial. Run the identical text through SupWriter's AI humanizer. Put both outputs into the detector your school or client actually uses (or GPTZero or Originality.ai if you do not know), save screenshots, then read the two side by side and ask which one you would actually submit under your own name.

That takes about five minutes and it beats trusting a comparison written by one of the two companies involved. Including this one.

---

Try it on your own text — 300 words free, no credit card required.