Best AI for essay writing / head-to-head

GPT-5.3-Codex vs GPT-5.6 Lunafor essay writing

The verdict

GPT-5.6 Luna wins, 9188

Same 12 essay writing tasks, marked blind by three rival labs. GPT-5.6 Luna took 3 tasks, GPT-5.3-Codex took 2, 7 tied. Tested 13 Aug 2026.

Where they differed most

The task — Essay plan

Produce a plan (not the essay) for a 2,000-word undergraduate essay on whether remote work has reduced productivity. Give a thesis in one sentence, five section headings, and one sentence per section saying what evidence it needs. Maximum 220 words total.

**Thesis (one sentence):**  
Remote work has not uniformly reduced productivity; its effects are heterogeneous across occupations, task types, and management practices, with average outcomes ranging from neutral to modestly positive when coordination systems are strong.

1. **Defining Productivity and Scope of the Question**  
Evidence needed: comparative definitions (output per hour, quality-adjusted output, innovation metrics) and boundary-setting data by sector (knowledge work vs. customer-facing/manual jobs) to avoid overgeneralization.

2.…
**Thesis:** Remote work has not uniformly reduced productivity: average effects are mixed or modest, with outcomes depending on job type, worker circumstances, management practices, and the quality of remote-work arrangements.

### 1. Introduction: Defining Productivity and Remote Work  
Use productivity measures (output per hour, performance ratings, innovation, and collaboration) and establish the distinction between fully remote, hybrid, and emergency work-from-home.

### 2. Evidence That Remote Work Can Maintain or Increase Productivity  
A…

Task by task

TaskGPT-5.3-CodexGPT-5.6 Luna
Structured argument85
Essay plan510
Tighten flabby prose1010
Hold a word count99
Adapt for the reader1010
Introduction only1010
Steelman the other side910
Cite honestly57
Fix the structure1010
Formal to plain108
Conclusion that adds something1010
Refuse to pad1010

Full receipts: GPT-5.3-Codex, GPT-5.6 Luna · judges claude-sonnet-5, gemini-3.1-pro-preview, grok-4.5

Questions people ask

Which is better for essay writing: GPT-5.3-Codex or GPT-5.6 Luna?

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.

More essay writing head-to-heads: GPT-5.6 Luna vs GPT-5.6 Sol · GPT-5.3-Codex vs GPT-5.6 Sol · GPT-5.5 vs GPT-5.6 Luna · GPT-5.3-Codex vs GPT-5.5 · GPT-5.6 Luna vs GPT-5.6 Terra · Claude Sonnet 5 vs GPT-5.6 Luna

Full ranking: Best AI for essay writing · model pages: GPT-5.3-Codex, GPT-5.6 Luna