Gemini 3.5 Flash vs GPT-5.6 Sol for code review
GPT-5.6 Sol wins, 96–84
Same 12 code review tasks, marked blind by three rival labs. GPT-5.6 Sol took 10 tasks, Gemini 3.5 Flash took 0, 2 tied. Tested 18 Aug 2026.
Where they differed most
Review this function. Context you can rely on, because it is validated upstream: `customers` and `outcodes` are always arrays; every customer object has a `postcode` property that is either a string or null; postcodes are stored either with or without the space ('SW1A 1AA' or 'SW1A1AA'); the required behaviour is to return the customers whose outward code matches one of `outcodes`, case-insensitively. function filterByOutcode(customers, outcodes) { const wanted = new Set(outcodes.map(o => o.trim().toUpperCase())); return customers.filter(c => { const pc = (c.postcode || '').trim().toUpperCase(); if (pc.length < 5) return false; const outward = pc.includes(' ') ? pc.split(' ')[0] : pc.slice(0, -3); return wanted.has(outward); }); } Give your review. If there are defects, list them by severity with the input that triggers each one. If there are none, say so plainly and briefly — do not manufacture a defect to look thorough, and do not dress a style preference up as a bug.
There are no defects in this function. Based on the provided context and the rules of UK postcodes (where the inward code is always the final 3 characters, and the minimum valid postcode length is 5 characters), the logic is robust, handles `null` values safely, correctly normalizes casing and spacing, and performs the lookups efficiently using a `Set`.
No defects under the stated validated inputs. The function correctly normalizes case and surrounding whitespace, handles postcodes with or without the standard space, safely rejects null postcodes, and matches the extracted outward code against the requested set.
Task by task
| Task | Gemini 3.5 Flash | GPT-5.6 Sol |
|---|---|---|
| The pagination that skips page one | 8 | 9 |
| Nothing wrong with it | 8 | 10 |
| Three things wrong in six lines | 8 | 9 |
| Two customers, one last item | 9 | 10 |
| Rank by what breaks | 8 | 9 |
| The review, as JSON | 8 | 10 |
| Slow is not the same as wrong | 8 | 10 |
| Overdue at one in the morning | 8 | 10 |
| Write only the comment | 10 | 10 |
| The complaint that is not a defect | 8 | 9 |
| Right, and unusable | 9 | 10 |
| Refuse the rubber stamp | 9 | 9 |
Full receipts: Gemini 3.5 Flash, GPT-5.6 Sol · judges claude-sonnet-5, gpt-5.6-terra, grok-4.5
Questions people ask
Which is better for code review: Gemini 3.5 Flash or GPT-5.6 Sol?
GPT-5.6 Sol — it scored 96/100 against 84/100 on our 12-task code review suite, winning 10 tasks to 0 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 code review 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 code review head-to-heads: GPT-5.5 vs GPT-5.6 Sol · Claude Sonnet 5 vs GPT-5.6 Sol · GPT-5.6 Sol vs Grok 4.5 · GLM 5.2 vs GPT-5.6 Sol · GPT-5.6 Sol vs Kimi K3 · Gemini 3.1 Pro Preview vs GPT-5.6 Sol
Full ranking: Best AI for code review · model pages: Gemini 3.5 Flash, GPT-5.6 Sol