Claude Sonnet 5 vs GPT-5.3-Codex for property and lettings admin

The verdict

GPT-5.3-Codex wins, 8885

Same 12 property and lettings admin tasks, marked blind by three rival labs. GPT-5.3-Codex took 5 tasks, Claude Sonnet 5 took 3, 4 tied. Tested 18 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.

# Answer Based Strictly on the Excerpt

## What the excerpt establishes about late protection

The excerpt is explicit on this point: **the failure is not cured simply by protecting the deposit late.** You are already past the deadline set out in legislation for both protecting the deposit and giving the tenant the prescribed information. Protecting it now, six weeks in, does not retrospectively make you compliant. "Doing it now and saying nothing" does not erase the breach that has already occurred.

## What protecting it now does and does not…
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…

Task by task

TaskClaude Sonnet 5GPT-5.3-Codex
Two routes, one worried tenant109
Six weeks late and hoping95
Write only the arrears email1010
The pre-tenancy checklist88
Write only the renewal reply1010
Three repairs, one Tuesday69
The nine-year-old carpet59
The rent rise by text message89
Every claim in the advert must be true89
The compliance data, as JSON1010
What the agent must not promise89
Refuse the lock change109

Full receipts: Claude Sonnet 5, GPT-5.3-Codex · judges gemini-3.1-pro-preview, gpt-5.6-terra, grok-4.5

Questions people ask

Which is better for property and lettings admin: Claude Sonnet 5 or GPT-5.3-Codex?

GPT-5.3-Codex — it scored 88/100 against 85/100 on our 12-task property and lettings admin suite, winning 5 tasks to 3 with 4 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-5.3-Codex vs GPT-5.6 Terra · Claude Sonnet 5 vs GPT-5.6 Terra · GPT-5.3-Codex vs GPT-5.5 · Claude Sonnet 5 vs GPT-5.5 · GPT-5.3-Codex vs GPT-5.6 Sol · Claude Sonnet 5 vs GPT-5.6 Sol

Full ranking: Best AI for property and lettings admin · model pages: Claude Sonnet 5, GPT-5.3-Codex