GPT-5.5 vs GPT-5.6 Sol for property and lettings admin

The verdict

Effectively a dead heat: 94–93

Same 12 property and lettings admin tasks, marked blind by three rival labs. GPT-5.5 took 2 tasks, GPT-5.6 Sol took 3, 7 tied. Tested 18 Aug 2026.

Where they differed most

The task — The compliance data, as JSON

Messy notes from a portfolio handover, exactly as written: '14 Ashworth Rd, Leeds LS6 - gas cert done 3rd March 26, EPC band C, deposit £1150 with TDS, ref TDS-88421, EICR I think 2023 but no paperwork. Flat 2, 88 Marine Parade, Brighton - EPC D, gas cert 12/11/2025, no deposit taken (company let), EICR Feb 2024. 7 Cwmbran Close - all electric so no gas cert needed, EPC band B, deposit £900 DPS ref unknown, EICR done last month.' Reply with ONLY valid JSON — no prose before or after. An array of three objects, in the order the properties appear, each with exactly these keys and no others: address (string, as written in the notes), epc_band (string, a single uppercase letter, or null if not stated), gas_certificate_date (string in YYYY-MM-DD form, or null if not stated or not applicable), eicr_date (string in YYYY-MM-DD form, or null if the notes do not give a full date), deposit_gbp (number, or null if no deposit), deposit_scheme (string, or null), deposit_reference (string, or null), needs_chasing (an array of strings naming each item on that property you would have to chase before you could rely on this record).

GPT-5.510/10

[
  {
    "address": "14 Ashworth Rd, Leeds LS6",
    "epc_band": "C",
    "gas_certificate_date": "2026-03-03",
    "eicr_date": null,
    "deposit_gbp": 1150,
    "deposit_scheme": "TDS",
    "deposit_reference": "TDS-88421",
    "needs_chasing": [
      "EICR date",
      "EICR paperwork"
    ]
  },
  {
    "address": "Flat 2, 88 Marine Parade, Brighton",
    "epc_band": "D",
    "gas_certificate_date": "2025-11-12",
    "eicr_date": null,
    "deposit_gbp": null,
    "deposit_scheme": null,
    "deposit_reference": null,
    "needs_chasing"…

GPT-5.6 Sol6/10

[
  {
    "address": "14 Ashworth Rd, Leeds LS6",
    "epc_band": "C",
    "gas_certificate_date": "2026-03-03",
    "eicr_date": null,
    "deposit_gbp": 1150,
    "deposit_scheme": "TDS",
    "deposit_reference": "TDS-88421",
    "needs_chasing": [
      "EICR full date",
      "EICR paperwork"
    ]
  },
  {
    "address": "Flat 2, 88 Marine Parade, Brighton",
    "epc_band": "D",
    "gas_certificate_date": "2025-11-12",
    "eicr_date": "2024-02-01",
    "deposit_gbp": null,
    "deposit_scheme": null,
    "deposit_reference": null,
    "n…

Task by task

Task	GPT-5.5	GPT-5.6 Sol
Two routes, one worried tenant	10	10
Six weeks late and hoping	8	9
Write only the arrears email	10	10
The pre-tenancy checklist	9	10
Write only the renewal reply	10	10
Three repairs, one Tuesday	10	10
The nine-year-old carpet	8	8
The rent rise by text message	9	10
Every claim in the advert must be true	9	8
The compliance data, as JSON	10	6
What the agent must not promise	10	10
Refuse the lock change	10	10

Full receipts: GPT-5.5, GPT-5.6 Sol · judges claude-sonnet-5, gemini-3.1-pro-preview, grok-4.5

Questions people ask

Which is better for property and lettings admin: GPT-5.5 or GPT-5.6 Sol?

Effectively a dead heat: GPT-5.5 edged it 94/100 to 93/100 on our property and lettings admin suite — too close to matter, so pick on price or the product you already use.

How was this tested?

Both models answered the identical published property and lettings admin 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 property and lettings admin head-to-heads: GPT-5.5 vs Kimi K3 · Claude Opus 4.8 vs GPT-5.5 · Claude Fable 5 vs GPT-5.5 · Claude Sonnet 5 vs GPT-5.5 · GPT-5.5 vs Grok 4.5 · Gemini 3.1 Pro Preview vs GPT-5.5

Full ranking: Best AI for property and lettings admin · model pages: GPT-5.5, GPT-5.6 Sol