Best AI for summarising documents / head-to-head
Claude Sonnet 5 vs GPT-5.3-Codexfor summarising documents
GPT-5.3-Codex wins, 96–93
Same 12 summarising documents tasks, marked blind by three rival labs. GPT-5.3-Codex took 2 tasks, Claude Sonnet 5 took 1, 9 tied. Tested 13 Aug 2026.
Where they differed most
From this thread, state in one line WHAT was decided and WHO decided it. If no decision was reached, say so. Thread: 'A: shall we move the launch to October? B: I'd rather not, the trade show is in September. A: agreed, but we can't ship without the packaging. C: packaging lands 2 Sept, confirmed by the printer this morning. A: fine, September stands then.'
**Decision:** The launch date will remain in September (not moved to October). **Decided by:** A (with agreement from B and confirmation from C on packaging timing).
Decision: **Keep the launch in September (not move to October)**, decided by **A** (after input from B and C).
Task by task
| Task | Claude Sonnet 5 | GPT-5.3-Codex |
|---|---|---|
| Meeting notes to actions | 9 | 9 |
| Five-bullet summary | 10 | 8 |
| Do not invent | 10 | 10 |
| One-sentence gist | 10 | 10 |
| Preserve the caveat | 10 | 10 |
| Summarise a disagreement | 9 | 9 |
| Extract the decision | 5 | 10 |
| Long to short, no loss | 10 | 10 |
| Summary for a specific reader | 9 | 9 |
| Bullet the risks only | 10 | 10 |
| Headline and standfirst | 9 | 10 |
| Say when there is nothing to summarise | 10 | 10 |
Full receipts: Claude Sonnet 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 summarising documents: Claude Sonnet 5 or GPT-5.3-Codex?
GPT-5.3-Codex — it scored 96/100 against 93/100 on our 12-task summarising documents suite, winning 2 tasks to 1 with 9 tied. Every answer was marked blind by three judges from three rival AI labs.
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 Claude Sonnet 5 · GPT-5.3-Codex vs GPT-5.5 · Claude Sonnet 5 vs GPT-5.5 · GPT-5.3-Codex vs GPT-5.6 Luna · Claude Sonnet 5 vs GPT-5.6 Luna
Full ranking: Best AI for summarising documents · model pages: Claude Sonnet 5, GPT-5.3-Codex