Claude Sonnet 5 vs GPT-5.6 Sol for bookkeeping
GPT-5.6 Sol wins, 93–81
Same 12 bookkeeping tasks, marked blind by three rival labs. GPT-5.6 Sol took 6 tasks, Claude Sonnet 5 took 1, 5 tied. Tested 18 Aug 2026.
Where they differed most
A bank reconciliation will not balance. The bank statement closing balance is £8,412.55. The cash book closing balance is £8,376.55. Outstanding items already accounted for: an unpresented cheque of £120.00 and a lodgement of £120.00 not yet on the statement, which cancel each other out. The bookkeeper has checked her additions twice. The cash book receipts for the month, as entered: £451.00, £1,208.30, £96.75, £2,340.00, £415.00, £188.50. The corresponding bank credits: £415.00, £1,208.30, £96.75, £2,340.00, £451.00, £188.50. Work out the difference, say what kind of error it is, explain the arithmetic rule that identifies this class of error at a glance, and say which side is wrong and how she would prove it. Then say what she should do about it in the ledger and what she should NOT do.
## Step 1 – Find the actual difference Bank statement balance: **£8,412.55** Cash book balance: **£8,376.55** Difference = £8,412.55 − £8,376.55 = **£36.00** The unpresented cheque and the outstanding lodgement are both £120.00, so they cancel out and are *not* the cause of the imbalance. The £36.00 has to be explained by something else. ## Step 2 – Spot the pattern in the receipts Line up the cash book receipts against the bank credits: | Cash book | Bank statement | |---|---| | 451.00 | 415.00 | | 1,208.30 | 1,208.30 | | 96.75 | 96.75 |…
- **Adjusted bank-statement balance:** £8,412.55 − £120 unpresented cheque + £120 outstanding lodgement = **£8,412.55** - **Difference:** £8,412.55 − £8,376.55 = **£36.00** Thus, if the statement is correct, the cash-book balance is £36 too low. ### Apparent type of error £36 has the classic signature of a **digit-transposition error**. For example: \[ £451-£415=£36 \] A reversal of digits always produces a difference divisible by **9**: \[ 451-415=36=9\times4 \] This is the “divisibility by 9” or “casting out nines” clue. It…
Task by task
| Task | Claude Sonnet 5 | GPT-5.6 Sol |
|---|---|---|
| The client lunch and the sandwich | 5 | 8 |
| Categorise, and admit what you cannot | 8 | 9 |
| The invoice totals | 10 | 10 |
| Find the £36 | 3 | 9 |
| Profit but no money | 9 | 8 |
| Not your decision to make | 10 | 10 |
| The faded shoebox | 8 | 10 |
| It is my company, it is my money | 6 | 8 |
| The mileage claim | 10 | 10 |
| Capital or revenue | 10 | 10 |
| Quote, invoice, receipt | 9 | 9 |
| Refuse the backdated invoice | 9 | 10 |
Full receipts: Claude Sonnet 5, GPT-5.6 Sol · judges gemini-3.1-pro-preview, gpt-5.6-terra, grok-4.5
Questions people ask
Which is better for bookkeeping: Claude Sonnet 5 or GPT-5.6 Sol?
GPT-5.6 Sol — it scored 93/100 against 81/100 on our 12-task bookkeeping 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 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-5.5 vs GPT-5.6 Sol · GPT-5.6 Sol vs Grok 4.5 · GPT-5.6 Sol vs Kimi K3 · Claude Opus 4.8 vs GPT-5.6 Sol · GLM 5.2 vs GPT-5.6 Sol · Gemini 3.5 Flash vs GPT-5.6 Sol
Full ranking: Best AI for bookkeeping · model pages: Claude Sonnet 5, GPT-5.6 Sol