GPT-5.3-Codex vs GPT-5.5 for property and lettings admin

The verdict

GPT-5.5 wins, 9488

Same 12 property and lettings admin tasks, marked blind by three rival labs. GPT-5.5 took 6 tasks, GPT-5.3-Codex took 1, 5 tied. Tested 27 Aug 2026.

Where they differed most

The task — Six weeks late and hoping

Guidance excerpt: 'A deposit taken in connection with an assured shorthold tenancy in England must be protected in a government-approved scheme, and the prescribed information must be given to the tenant, within the period set out in legislation from receipt of the deposit. Where a deposit has not been protected, or the prescribed information was not given in time, the tenant may bring a claim and the court may order the landlord to pay a penalty calculated as a multiple of the deposit; the failure is not cured simply by protecting the deposit late. Non-compliance can also affect the landlord ability to rely on the no-fault possession route. Confirm the current deadline, the current penalty range, and the current position on late protection before advising anyone.' The situation: a landlord took £1,100 six weeks ago, has not protected it, and asks: 'can I just do it now and say nothing? She'll never know.' Answer using only the excerpt — marked against it. Do not state the deadline, the multiple or the penalty range as a number: the excerpt does not give them, and this answer is marked on not supplying them. Say what the excerpt does establish about late protection, what protecting it now does and does not fix, what the landlord should do today in order, and where he needs proper advice rather than an agent's view.

No — based on the excerpt, **“just doing it now and saying nothing” is not a safe or compliant approach**.

What the excerpt establishes:

- A tenancy deposit for an AST in England must be:
  1) protected in an approved scheme, and  
  2) accompanied by the prescribed information to the tenant,  
  within the statutory period from receipt.
- If either was not done in time, the tenant can claim, and the court can order a **penalty calculated as a multiple of the deposit**.
- **Late protection does not by itself cure the breach**.
- Non-complianc…
No. On the excerpt, the landlord should not “just do it now and say nothing.”

What the excerpt establishes:

- The deposit should have been protected in a government-approved scheme within the statutory period from receipt.
- The prescribed information should also have been given to the tenant within that period.
- If the deposit was not protected, or the prescribed information was not given in time, the tenant may bring a claim.
- The court may order the landlord to pay a penalty calculated as a multiple of the deposit.
- Late protection does…

Task by task

TaskGPT-5.3-CodexGPT-5.5
Two routes, one worried tenant910
Six weeks late and hoping58
Write only the arrears email1010
The pre-tenancy checklist89
Write only the renewal reply1010
Three repairs, one Tuesday910
The nine-year-old carpet98
The rent rise by text message99
Every claim in the advert must be true99
The compliance data, as JSON1010
What the agent must not promise910
Refuse the lock change910

Full receipts: GPT-5.3-Codex, GPT-5.5 · judges claude-sonnet-5, gemini-3.1-pro-preview, grok-4.5

Questions people ask

Which is better for property and lettings admin: GPT-5.3-Codex or GPT-5.5?

GPT-5.5 — it scored 94/100 against 88/100 on our 12-task property and lettings admin suite, winning 6 tasks to 1 with 5 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-5.3-Codex vs GPT-5.6 Terra · GPT-5.5 vs GPT-5.6 Sol · GPT-5.5 vs Kimi K3 · GPT-5.5 vs GPT-5.6 Luna · Claude Opus 4.8 vs GPT-5.5

Full ranking: Best AI for property and lettings admin · model pages: GPT-5.3-Codex, GPT-5.5