GPT-5.5 vs Grok 4.5 for multi-step research
GPT-5.5 wins, 91–85
Same 12 multi-step research tasks, marked blind by three rival labs. GPT-5.5 took 8 tasks, Grok 4.5 took 3, 1 tied. Tested 18 Aug 2026.
Where they differed most
Three sources on the average deposit a UK first-time buyer needs. Source A — a high-street lender, 2025: '£53,414', based on mortgages it approved that year. Source B — a building society, 2025: '£34,500', first-time buyers outside London. Source C — a London estate agency, 2024: '£71,000'. These are usually written up as a contradiction. Show that they are not: name the hidden variable inside each figure (who is counted, where, when, and what counts as a deposit), and explain which comparison would be needed before any two of them could disagree. Then write the one sentence about first-time-buyer deposits that is true given all three, and name the thing a specific reader — a couple saving in Derby — still cannot learn from any of them.
They are not a contradiction because each number has different hidden conditions. | Source | Who is counted | Where | When | What “deposit” means / may mean | |---|---|---|---|---| | A: high-street lender, **£53,414** | First-time buyers whose mortgages **that lender approved** — not all first-time buyers | UK-wide, so London and non-London are mixed | 2025 | The actual deposit on approved mortgage cases; not necessarily the minimum required, and not necessarily total savings needed including fees | | B: building society, **£34,500** | First-t…
**They are not in contradiction.** Each figure embeds a different hidden variable (different who/where/when/definition), so they answer different questions. - **Source A (£53,414)**: mean deposit on mortgages *this specific high-street lender actually approved* in 2025 (its own customer mix, UK-wide including London, deposits as recorded on those approvals). - **Source B (£34,500)**: figure for first-time buyers *outside London* (building-society sample/definition, 2025). - **Source C (£71,000)**: figure from a *London* estate agency’s transac…
Task by task
| Task | GPT-5.5 | Grok 4.5 |
|---|---|---|
| Four numbers, one high street | 9 | 8 |
| The trial that both worked and didn't | 9 | 8 |
| Break the brief into answerable steps | 8 | 9 |
| Corroboration that isn't | 9 | 8 |
| The disagreement is definitional | 9 | 7 |
| A forecast is not an outcome | 10 | 8 |
| The evidence table, as JSON | 9 | 10 |
| Funded, and still the best data | 9.5 | 8 |
| Write only the limits section | 9 | 9 |
| Not answerable from what you have | 10 | 9 |
| The statistic and the doorstep | 9 | 8 |
| Refuse the manufactured briefing | 9 | 10 |
Full receipts: GPT-5.5, Grok 4.5 · judges claude-sonnet-5, gemini-3.1-pro-preview, grok-4.5
Questions people ask
Which is better for multi-step research: GPT-5.5 or Grok 4.5?
GPT-5.5 — it scored 91/100 against 85/100 on our 12-task multi-step research suite, winning 8 tasks to 3 with 1 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 Grok 4.5 · GPT-5.5 vs GPT-5.6 Sol · GPT-5.5 vs Kimi K3 · Claude Opus 4.8 vs GPT-5.5 · Gemini 3.1 Pro Preview vs GPT-5.5
Full ranking: Best AI for multi-step research · model pages: GPT-5.5, Grok 4.5