GPT-5.6 Luna vs GPT-5.6 Terra for bookkeeping
GPT-5.6 Terra wins, 93–83
Same 12 bookkeeping tasks, marked blind by three rival labs. GPT-5.6 Terra took 6 tasks, GPT-5.6 Luna took 2, 4 tied. Tested 27 Aug 2026.
Where they differed most
Guidance excerpt: 'Where an employee or director uses their own car for business travel, an employer may pay approved mileage allowance without it being taxable, up to 45p per mile for the first 10,000 business miles in the tax year and 25p per mile for each business mile after that. Travel between home and a permanent workplace is ordinary commuting and is not business travel. Records must show the date, the journey, the reason and the mileage.' The claim submitted: 'Total miles driven this year 18,700. Of that, 12,400 was for work. The other 6,300 is personal, which includes 900 miles driven from my house to the office and back.' Answer using only the excerpt above — marked against it. Show the arithmetic openly, line by line, state the figure that can be paid without a tax charge, deal explicitly with the 900 miles, and say what is missing from this claim before it can be paid at all.
The 900 miles from home to the office are ordinary commuting, not business travel, so they must be excluded. **Arithmetic:** - Total miles: **18,700** - Claimed work miles: **12,400** - Less home-to-office commuting: **900** - Allowable business miles: **12,400 − 900 = 11,500** Mileage allowance: - First 10,000 business miles: **10,000 × 45p = £4,500** - Remaining 1,500 business miles: **1,500 × 25p = £375** - Total payable without a tax charge: **£4,500 + £375 = £4,875** The claim’s stated personal miles would also need to be adjusted: **…
**Mileage that qualifies as business travel:** 12,400 miles The 900 miles from home to the office and back are **ordinary commuting**, not business travel. They cannot be included in tax-free approved mileage allowance. On the figures given, they are already included within the 6,300 personal miles, not the 12,400 work miles. **Tax-free approved mileage calculation:** - First 10,000 business miles × 45p = **£4,500** - Remaining business miles: 12,400 − 10,000 = 2,400 miles - 2,400 miles × 25p = **£600** **Total that can be paid without a ta…
Task by task
| Task | GPT-5.6 Luna | GPT-5.6 Terra |
|---|---|---|
| The client lunch and the sandwich | 9 | 8 |
| Categorise, and admit what you cannot | 9 | 10 |
| The invoice totals | 10 | 10 |
| Find the £36 | 8 | 8 |
| Profit but no money | 5 | 9 |
| Not your decision to make | 10 | 9 |
| The faded shoebox | 9 | 10 |
| It is my company, it is my money | 8 | 8 |
| The mileage claim | 3 | 10 |
| Capital or revenue | 9 | 10 |
| Quote, invoice, receipt | 9 | 10 |
| Refuse the backdated invoice | 10 | 10 |
Full receipts: GPT-5.6 Luna, GPT-5.6 Terra · judges claude-sonnet-5, gemini-3.1-pro-preview, grok-4.5
Questions people ask
Which is better for bookkeeping: GPT-5.6 Luna or GPT-5.6 Terra?
GPT-5.6 Terra — it scored 93/100 against 83/100 on our 12-task bookkeeping suite, winning 6 tasks to 2 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 bookkeeping 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 bookkeeping head-to-heads: GPT-5.6 Sol vs GPT-5.6 Terra · GPT-5.3-Codex vs GPT-5.6 Terra · GPT-5.5 vs GPT-5.6 Terra · Claude Fable 5 vs GPT-5.6 Terra · GPT-5.6 Terra vs Grok 4.5 · GPT-5.6 Terra vs Qwen3.7 Max
Full ranking: Best AI for bookkeeping · model pages: GPT-5.6 Luna, GPT-5.6 Terra