Best AI for essay writing / head-to-head
GPT-5.6 Luna vs GPT-5.6 Terrafor essay writing
GPT-5.6 Luna wins, 91–88
Same 12 essay writing tasks, marked blind by three rival labs. GPT-5.6 Luna took 3 tasks, GPT-5.6 Terra took 2, 7 tied. Tested 13 Aug 2026.
Where they differed most
This paragraph makes three points at once and repeats itself. Rewrite it as three short paragraphs, one point each, no repetition: 'Exercise is good for your body and it also helps your mood, and being active reduces the risk of heart disease, plus people who exercise often sleep better, and of course it is good for the heart.'
Exercise supports physical health and reduces the risk of heart disease. Regular activity can improve your mood. People who exercise often sleep better.
Exercise supports overall physical health. Regular activity can improve mood and lower the risk of heart disease. People who exercise often sleep better.
Task by task
| Task | GPT-5.6 Luna | GPT-5.6 Terra |
|---|---|---|
| Structured argument | 5 | 8 |
| Essay plan | 10 | 9 |
| Tighten flabby prose | 10 | 10 |
| Hold a word count | 9 | 9 |
| Adapt for the reader | 10 | 10 |
| Introduction only | 10 | 10 |
| Steelman the other side | 10 | 10 |
| Cite honestly | 7 | 5 |
| Fix the structure | 10 | 5 |
| Formal to plain | 8 | 9 |
| Conclusion that adds something | 10 | 10 |
| Refuse to pad | 10 | 10 |
Full receipts: GPT-5.6 Luna, GPT-5.6 Terra · judges claude-sonnet-5, gemini-3.1-pro-preview, grok-4.5
Questions people ask
Which is better for essay writing: GPT-5.6 Luna or GPT-5.6 Terra?
GPT-5.6 Luna — it scored 91/100 against 88/100 on our 12-task essay writing suite, winning 3 tasks to 2 with 7 tied. Every answer was marked blind by three judges from three rival AI labs.
How was this tested?
Both models answered the identical published essay writing 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.
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Full ranking: Best AI for essay writing · model pages: GPT-5.6 Luna, GPT-5.6 Terra