Best AI for writing emails / head-to-head
DeepSeek V4 Pro vs GLM 5.2for writing emails
Dead heat: 93 each
Same 12 writing emails tasks, marked blind by three rival labs. Tested 14 Aug 2026.
Where they differed most
Write an email (max 130 words) telling a customer their delivery will be 2 weeks late because a supplier failed. Take responsibility without blaming the supplier by name, offer one concrete remedy, and do not use the phrase 'we apologise for any inconvenience'.
Subject: Update on your delivery timeline Dear [Customer Name], I’m writing to let you know that your order will arrive two weeks later than originally promised. We recently faced an unexpected failure in our supply chain, and as a result, we haven’t been able to meet the timeline we set together. This falls entirely on us, and I’m truly sorry. To make this right, I’ve applied a 15% discount to your order, which will be reflected in your final invoice. You don’t need to take any action—the adjustment is already in place. We’re worki…
Subject: Update on your order delivery Dear [Customer Name], I am writing to let you know that your order will be delayed by two weeks. We take full responsibility for this delay, as we encountered an unexpected issue with our supply chain that prevented us from receiving the necessary materials on time. To help make up for this wait, we are issuing a 20% refund to your original payment method today. We value your business and are working hard to get your items to you by [Date]. Please let us know if you have any questions. Best regards,…
Task by task
| Task | DeepSeek V4 Pro | GLM 5.2 |
|---|---|---|
| Chase an unpaid invoice | 10 | 8 |
| Decline a meeting politely | 10 | 10 |
| Give bad news | 5 | 10 |
| Introduce two people | 8 | 8 |
| Subject lines that inform | 9 | 10 |
| Reply to an angry email | 10 | 8 |
| Ask for a pay rise meeting | 10 | 10 |
| Cancel a contract cleanly | 10 | 10 |
| The one-line email | 10 | 10 |
| Out of office that helps | 10 | 10 |
| Follow up without nagging | 10 | 8 |
| Refuse to write it | 10 | 10 |
Full receipts: DeepSeek V4 Pro, GLM 5.2 · judges claude-sonnet-5, gemini-3.1-pro-preview, gpt-5.6-terra
Questions people ask
Which is better for writing emails: DeepSeek V4 Pro or GLM 5.2?
They tied at 93/100 on our writing emails suite — for this job, pick on price or the product you already use.
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: DeepSeek V4 Pro vs GPT-5.3-Codex · GLM 5.2 vs GPT-5.3-Codex · DeepSeek V4 Pro vs GPT-5.6 Sol · GLM 5.2 vs GPT-5.6 Sol · DeepSeek V4 Pro vs GPT-5.5 · GLM 5.2 vs GPT-5.5
Full ranking: Best AI for writing emails · model pages: DeepSeek V4 Pro, GLM 5.2