Gemini 3.1 Pro Preview vs GPT-5.5 for multi-step research
GPT-5.5 wins, 91–82
Same 12 multi-step research tasks, marked blind by three rival labs. GPT-5.5 took 9 tasks, Gemini 3.1 Pro Preview took 1, 2 tied. Tested 18 Aug 2026.
Where they differed most
Three extracts on whether a town's new 20mph zone reduced injuries. A: 'road casualties within the zone fell from 31 in the year before to 22 in the year after (council road safety report, 2026).' B: 'casualties fell across the whole borough over the same period, including in streets with no speed change (borough-wide figures, 2026).' C: 'average speeds inside the zone fell by 2.1mph; 41% of vehicles still exceeded 20mph (survey commissioned by the campaign group that lobbied for the zone, 2025).' Reply with ONLY valid JSON — no prose before or after. An array of objects, one per claim you are prepared to make, each with exactly these keys and no others: claim (string), supported_by (array of the source letters), contradicted_or_weakened_by (array of source letters, empty if none), confidence (one of 'high', 'medium', 'low'), not_established (string saying what this claim still does not settle).
[
{
"claim": "Road casualties within the designated 20mph zone decreased in the year following its introduction.",
"supported_by": [
"A"
],
"contradicted_or_weakened_by": [],
"confidence": "high",
"not_established": "Whether this absolute reduction in casualties was directly caused by the new speed limit."
},
{
"claim": "The implementation of the 20mph zone was the primary cause of the reduced casualty rate within its boundaries.",
"supported_by": [
"A"
],
"contradicted_or_weakened_by":…[
{
"claim": "Reported road casualties within the 20mph zone fell from 31 in the year before to 22 in the year after.",
"supported_by": [
"A"
],
"contradicted_or_weakened_by": [],
"confidence": "high",
"not_established": "This before-after change alone does not settle whether the 20mph zone caused the reduction, whether the change is statistically significant, or whether it persisted beyond one year."
},
{
"claim": "The casualty fall inside the zone cannot be confidently attributed to the 20mph limit on t…Task by task
| Task | Gemini 3.1 Pro Preview | GPT-5.5 |
|---|---|---|
| Four numbers, one high street | 8 | 9 |
| The trial that both worked and didn't | 8 | 9 |
| Break the brief into answerable steps | 10 | 8 |
| Corroboration that isn't | 8 | 9 |
| The disagreement is definitional | 8 | 9 |
| A forecast is not an outcome | 8 | 10 |
| The evidence table, as JSON | 6 | 9 |
| Funded, and still the best data | 7 | 9.5 |
| Write only the limits section | 9 | 9 |
| Not answerable from what you have | 10 | 10 |
| The statistic and the doorstep | 8 | 9 |
| Refuse the manufactured briefing | 8 | 9 |
Full receipts: Gemini 3.1 Pro Preview, GPT-5.5 · judges claude-sonnet-5, gpt-5.6-terra, grok-4.5
Questions people ask
Which is better for multi-step research: Gemini 3.1 Pro Preview or GPT-5.5?
GPT-5.5 — it scored 91/100 against 82/100 on our 12-task multi-step research suite, winning 9 tasks to 1 with 2 tied. Every answer was marked blind by three judges from three rival AI labs.
How was this tested?
Both models answered the identical published multi-step research 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 multi-step research head-to-heads: Claude Sonnet 5 vs GPT-5.5 · Claude Sonnet 5 vs Gemini 3.1 Pro Preview · GPT-5.5 vs GPT-5.6 Sol · GPT-5.5 vs Kimi K3 · GPT-5.5 vs Grok 4.5 · Claude Opus 4.8 vs GPT-5.5
Full ranking: Best AI for multi-step research · model pages: Gemini 3.1 Pro Preview, GPT-5.5