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October 2026 review · same 50 texts

Undetectable.ai vs Rephrasy

In the October 2026 HumanizerEval review, Undetectable.ai and Rephrasy rewrote the same 50 English texts. Undetectable.ai cleared all 6 detectors on 1 of them; Rephrasy on 0. The difference is mostly GPTZero: on 10 samples Undetectable.ai passed it where Rephrasy failed, and the reverse happened on 2. On Originality.ai 5.0 and Winston AI the two were close to even.

Per-sample agreement

Per-sample agreement, October 2026. Counts are out of the 50 shared samples, computed at the 50% human-score threshold. Margin counts the samples only one tool passed, higher count first.
DetectorPassed more oftenMarginBoth passedNeither passed
Pangram 4.1Undetectable.ai11 to 4926
GPTZero 2026-10-07-baseUndetectable.ai10 to 2335
Originality.ai TurboUndetectable.ai7 to 1420
Originality.ai 5.0 model-5.0Undetectable.ai2 to 0048
ZeroGPT defaultUndetectable.ai4 to 0460
Winston AI 5.0Tied0 to 0500
All 6 detectorsUndetectable.ai1 to 0049

Every count is computed from scores.csv at build time, not transcribed. “Neither passed” counts the texts that defeated both tools; on Pangram that was 26 of 50 here.

Quality and output discipline

Quality and output discipline, October 2026.
MeasureUndetectable.aiRephrasy
32%32%
28%44%
90%98%
60%62%
1.271.22
115
00
University / General Writing / More Human, v11srv4
Websiteundetectable.ai rephrasy.ai

On per-sample quality scores, Undetectable.ai scored higher on 13 samples, Rephrasy on 22, and the two tied on 15. Rephrasy’s output was shorter on 39 of 50 samples; mean length ratios were 1.27 and 1.22, or 27% longer than the input and 22% longer than the input respectively.

Where each one outperforms the other

Undetectable.ai

  • Pangram: passed 20 of 50 against 13, including 11 samples where Rephrasy failed, against 4 the other way.
  • GPTZero: passed 43 of 50 against 35, including 10 samples where Rephrasy failed, against 2 the other way.
  • Originality.ai Turbo: passed 49 of 50 against 43, including 7 samples where Rephrasy failed, against 1 the other way.
  • Originality.ai 5.0: passed 2 of 50 against 0, including 2 samples where Rephrasy failed, against 0 the other way.
  • ZeroGPT: passed 50 of 50 against 46, including 4 samples where Rephrasy failed, against 0 the other way.
  • Winston AI: tied at 50 of 50 but on a higher mean human score, 98.5% to 98.4%. It passed 0 samples where Rephrasy failed.

Rephrasy

  • Pangram: passed 4 samples where Undetectable.ai failed, even though it was detected more often overall, passing 13 to 20.
  • GPTZero: passed 2 samples where Undetectable.ai failed, even though it was detected more often overall, passing 35 to 43.
  • Originality.ai Turbo: passed 1 sample where Undetectable.ai failed, even though it was detected more often overall, passing 43 to 49.
  • Naturalness: 44% against 28%.
  • Syntax integrity: 98% against 90%.
  • Stance preservation: 62% against 60%.
  • Length: shorter output on 39 of 50 samples, which matters under a word limit.

Undetectable.ai vs Rephrasy FAQ

Is Undetectable.ai better than Rephrasy?

In the October 2026 HumanizerEval review, Undetectable.ai cleared all 6 detectors on 1 of the 50 shared samples and Rephrasy on 0. On Originality.ai 5.0 and Winston AI the two were within 6 points of each other. Quality ran 13 samples to 22, with 15 ties.

Which humanizer is best for Pangram, Undetectable.ai or Rephrasy?

Undetectable.ai. In October 2026, Undetectable.ai passed Pangram on 20 of the 50 shared samples and Rephrasy on 13. On 11 samples Undetectable.ai passed where Rephrasy failed; the reverse happened on 4. Both failed on 26.

Which humanizer changes the text less?

Rephrasy. It scored higher on per-sample quality on 22 of 50 samples, against 13. Undetectable.ai’s outputs averaged 1.27× the input length and passed factual consistency on 32%; Rephrasy’s averaged 1.22× and passed on 32%. On stance preservation the split was 60% to 62%. Rephrasy produced the shorter output on 39 of 50 samples.

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