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

The verdict

GPT-5.5 wins, 9489

Same 12 property and lettings admin tasks, marked blind by three rival labs. GPT-5.5 took 5 tasks, GPT-5.6 Luna took 1, 6 tied. Tested 18 Aug 2026.

Where they differed most

The task — The pre-tenancy checklist

Guidance excerpt: 'Before a new assured shorthold tenancy in England begins, a landlord or agent is generally expected to have the following in place. (1) A current gas safety record where there are gas appliances, renewed every 12 months, with a copy given to the tenant before they move in. (2) An Electrical Installation Condition Report, normally renewed at least every 5 years, with a copy given to the tenant before occupation. (3) A valid Energy Performance Certificate, given to the tenant, with the property meeting the minimum energy efficiency standard that applies. (4) Working smoke alarms on every storey and a carbon monoxide alarm in any room with a fixed combustion appliance, tested at the start of the tenancy. (5) The current government How to Rent guide, served in the correct format. (6) Any licence required by the local authority for the property, which varies by area and by property type. Requirements change: confirm the current position with the local authority and at source before letting.' A tenancy starts on 1 October. Return only the checklist — exactly 6 bullets, in the order given above, one line each, no sub-points, no preamble. Each line: what it is, when it must be done by, and what the excerpt says happens or is required. Where the excerpt gives no renewal period or deadline for that item, say so on that line and name what you would check.

- Gas safety record — by 1 October/before the tenant moves in; renewed every 12 months, with a copy given to the tenant before move-in where there are gas appliances.
- Electrical Installation Condition Report — by 1 October/before occupation; normally renewed at least every 5 years, with a copy given to the tenant before occupation.
- Energy Performance Certificate — by 1 October/given to the tenant before the tenancy begins; no renewal period stated, so check the current EPC validity rules and minimum energy efficiency standard at source.
- S…
- Gas safety record: have a current record before the tenancy begins, renew every 12 months, and give a copy to the tenant before they move in.
- Electrical Installation Condition Report: have it before occupation, normally renew at least every 5 years, and give a copy to the tenant before occupation.
- Energy Performance Certificate: provide a valid EPC before letting or occupation and ensure the property meets the applicable minimum energy-efficiency standard; no renewal deadline is stated, so check the current requirements at source.
- Smoke…

Task by task

TaskGPT-5.5GPT-5.6 Luna
Two routes, one worried tenant108
Six weeks late and hoping810
Write only the arrears email1010
The pre-tenancy checklist96
Write only the renewal reply1010
Three repairs, one Tuesday109
The nine-year-old carpet88
The rent rise by text message99
Every claim in the advert must be true99
The compliance data, as JSON109
What the agent must not promise109
Refuse the lock change1010

Full receipts: GPT-5.5, GPT-5.6 Luna · 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 Luna?

GPT-5.5 — it scored 94/100 against 89/100 on our 12-task property and lettings admin suite, winning 5 tasks to 1 with 6 tied. Every answer was marked blind by three judges from three rival AI labs.

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 GPT-5.6 Terra · GPT-5.6 Luna vs GPT-5.6 Terra · GPT-5.5 vs GPT-5.6 Sol · GPT-5.5 vs Kimi K3 · Claude Opus 4.8 vs GPT-5.5 · GPT-5.3-Codex vs GPT-5.5

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