Claude Fable 5 vs GPT-5.3-Codex for humanising AI text
Effectively a dead heat: 97–95
Same 12 humanising AI text tasks, marked blind by three rival labs. GPT-5.3-Codex took 2 tasks, Claude Fable 5 took 0, 10 tied. Tested 16 Aug 2026.
Where they differed most
Rewrite this so it sounds like a person wrote it, keeping every fact — the invoice number, the amount, the due date, the attachment: 'I hope this email finds you well. I am reaching out to touch base regarding the outstanding invoice #2214 for £340, which was due on 14 July. Please do not hesitate to review the attached document at your earliest convenience. I look forward to hearing from you soon and thank you in advance for your cooperation.' Same politeness, human voice, probably shorter.
Here's a version that keeps everything but drops the corporate autopilot tone: --- Hi [Name], Just a quick nudge about invoice #2214 for £340 — it was due on 14 July and I don't think it's come through yet. I've attached a copy in case it's easier to have it to hand. Let me know if there's anything you need from me. Thanks so much! Best, [Your name] --- A few notes on what changed: - **"I hope this email finds you well"** and **"touch base"** are gone — they're the fastest way to sound like a template. - **"Please do not hesitate to..."*…
Hi [Name], I hope you’re well. Just a quick follow-up on invoice **#2214** for **£340**, which was due on **14 July**. I’ve attached it here for your review when you have a moment. Thanks in advance, and I look forward to hearing from you. Best, [Your Name]
Task by task
| Task | Claude Fable 5 | GPT-5.3-Codex |
|---|---|---|
| The touching-base email | 9 | 10 |
| De-guru the bio | 10 | 10 |
| Product page, human voice | 9 | 10 |
| Strip the tics | 9 | 9 |
| The head's newsletter | 10 | 10 |
| The condolence card | 10 | 10 |
| Reply to the review, humanly | 10 | 10 |
| About us, actually about us | 10 | 10 |
| Best man, not best template | 9 | 9 |
| Human but still formal | 9 | 9 |
| Change log required | 9 | 9 |
| Refuse the disguise job | 10 | 10 |
Full receipts: Claude Fable 5, GPT-5.3-Codex · judges gemini-3.1-pro-preview, gpt-5.6-terra, grok-4.5
Questions people ask
Which is better for humanising AI text: Claude Fable 5 or GPT-5.3-Codex?
Effectively a dead heat: GPT-5.3-Codex edged it 97/100 to 95/100 on our humanising AI text suite — too close to matter, so pick on price or the product you already use.
How was this tested?
Both models answered the identical published humanising AI text tasks. Three AI judges from three different labs scored every answer blind against a fixed rubric; mechanically checkable rules (word limits, banned phrases) are enforced by the test harness in code. The raw outputs and judge verdicts are downloadable.
More humanising AI text head-to-heads: Claude Sonnet 5 vs GPT-5.3-Codex · GPT-5.3-Codex vs GPT-5.6 Sol · GPT-5.3-Codex vs GPT-5.5 · GLM 5.2 vs GPT-5.3-Codex · GPT-5.3-Codex vs GPT-5.6 Terra · GPT-5.3-Codex vs Qwen3.7 Max
Full ranking: Best AI for humanising AI text · model pages: Claude Fable 5, GPT-5.3-Codex