Best AI for summarising documents / head-to-head
GPT-5.3-Codex vs GPT-5.6 Terrafor summarising documents
Dead heat: 96 each
Same 12 summarising documents tasks, marked blind by three rival labs. Tested 13 Aug 2026.
Where they differed most
Summarise in exactly 5 bullets, max 15 words each, readable in 20 seconds: 'Our Q3 revenue rose 12% to £1.4m, driven mainly by the new retail channel which contributed £310k. Margins slipped from 41% to 37% because of higher shipping costs and a one-off warehouse move. Headcount stayed flat at 34. The main risk into Q4 is the supplier contract, which expires in November and has not been renegotiated. Cash at bank is £620k.'
- Q3 revenue increased 12% to £1.4m. - New retail channel drove growth, contributing £310k. - Margins fell from 41% to 37% due shipping costs and warehouse move. - Headcount remained unchanged at 34 employees. - Q4 risk: November supplier contract unrenegotiated; cash at bank is £620k.
- Q3 revenue rose 12% to £1.4m, driven by £310k from retail. - Margins fell from 41% to 37% due to shipping and warehouse move costs. - Headcount remained flat at 34 employees. - Key Q4 risk: supplier contract expires in November without renegotiation. - Cash at bank stood at £620k.
Task by task
| Task | GPT-5.3-Codex | GPT-5.6 Terra |
|---|---|---|
| Meeting notes to actions | 9 | 9 |
| Five-bullet summary | 8 | 10 |
| Do not invent | 10 | 10 |
| One-sentence gist | 10 | 8 |
| Preserve the caveat | 10 | 9 |
| Summarise a disagreement | 9 | 10 |
| Extract the decision | 10 | 10 |
| Long to short, no loss | 10 | 10 |
| Summary for a specific reader | 9 | 10 |
| Bullet the risks only | 10 | 10 |
| Headline and standfirst | 10 | 9 |
| Say when there is nothing to summarise | 10 | 10 |
Full receipts: GPT-5.3-Codex, GPT-5.6 Terra · judges claude-sonnet-5, gemini-3.1-pro-preview, grok-4.5
Questions people ask
Which is better for summarising documents: GPT-5.3-Codex or GPT-5.6 Terra?
They tied at 96/100 on our summarising documents suite — for this job, pick on price or the product you already use.
How was this tested?
Both models answered the identical published summarising documents 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 summarising documents head-to-heads: Claude Opus 4.8 vs GPT-5.3-Codex · Claude Opus 4.8 vs GPT-5.6 Terra · GPT-5.3-Codex vs GPT-5.5 · GPT-5.5 vs GPT-5.6 Terra · GPT-5.3-Codex vs GPT-5.6 Luna · GPT-5.6 Luna vs GPT-5.6 Terra
Full ranking: Best AI for summarising documents · model pages: GPT-5.3-Codex, GPT-5.6 Terra