Best AI for writing emails / head-to-head
GLM 5.2 vs GPT-5.6 Lunafor writing emails
GPT-5.6 Luna wins, 97–93
Same 12 writing emails tasks, marked blind by three rival labs. GPT-5.6 Luna took 4 tasks, GLM 5.2 took 2, 6 tied. Tested 14 Aug 2026.
Where they differed most
Write an email chasing invoice #1042, now 21 days overdue, to a long-standing client. Firm but warm, under 110 words, must state the amount is £1,840, must not use the word 'unfortunately', and must end with one specific next step.
Subject: Friendly reminder: Invoice #1042 Dear [Client Name], I hope you’re doing well. I’m reaching out regarding Invoice #1042 for £1,840, which is now 21 days overdue. We truly value our long-standing partnership and always appreciate your prompt payments, so I imagine this may have just slipped through the cracks. Could you please arrange for the £1,840 to be paid by the end of this week? Please reply to this email with the expected payment date so I can update our accounts accordingly. Warm regards, [Your Name]
**Subject: Invoice #1042 – 21 days overdue** Hi [Name], I hope you’re well. As a valued long-standing client, we appreciate our relationship and wanted to follow up on invoice #1042 for **£1,840**, which is now 21 days overdue. Could you please check its status and let us know if there’s anything holding up payment? We’d appreciate your prompt attention so we can keep our accounts up to date. **Please arrange payment of £1,840 within the next five working days.** Best, [Your Name]
Task by task
| Task | GLM 5.2 | GPT-5.6 Luna |
|---|---|---|
| Chase an unpaid invoice | 8 | 10 |
| Decline a meeting politely | 10 | 10 |
| Give bad news | 10 | 10 |
| Introduce two people | 8 | 9 |
| Subject lines that inform | 10 | 8 |
| Reply to an angry email | 8 | 10 |
| Ask for a pay rise meeting | 10 | 10 |
| Cancel a contract cleanly | 10 | 10 |
| The one-line email | 10 | 9 |
| Out of office that helps | 10 | 10 |
| Follow up without nagging | 8 | 10 |
| Refuse to write it | 10 | 10 |
Full receipts: GLM 5.2, GPT-5.6 Luna · judges claude-sonnet-5, gemini-3.1-pro-preview, gpt-5.6-terra
Questions people ask
Which is better for writing emails: GLM 5.2 or GPT-5.6 Luna?
GPT-5.6 Luna — it scored 97/100 against 93/100 on our 12-task writing emails suite, winning 4 tasks to 2 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 writing emails 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 writing emails head-to-heads: GPT-5.3-Codex vs GPT-5.6 Luna · GLM 5.2 vs GPT-5.3-Codex · GPT-5.6 Luna vs GPT-5.6 Sol · GLM 5.2 vs GPT-5.6 Sol · GPT-5.5 vs GPT-5.6 Luna · GLM 5.2 vs GPT-5.5
Full ranking: Best AI for writing emails · model pages: GLM 5.2, GPT-5.6 Luna