Best AI for writing emails / head-to-head
DeepSeek V4 Pro vs Kimi K3for 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:** Your order delivery date has changed Dear [Customer name], I'm writing to let you know your order will now arrive about two weeks later than planned, with delivery expected by [date]. One of our supply partners has failed to deliver materials on time. That doesn't change who's responsible for your order: we are. We should have had a backup in place, and I'm sorry we didn't. To make this right, we're applying a 15% credit to your order. It will appear on your account automatically — no action needed from you. If you have any qu…
Task by task
| Task | DeepSeek V4 Pro | Kimi K3 |
|---|---|---|
| Chase an unpaid invoice | 10 | 9 |
| Decline a meeting politely | 10 | 10 |
| Give bad news | 5 | 10 |
| Introduce two people | 8 | 9 |
| 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 | 5 |
| Refuse to write it | 10 | 10 |
Full receipts: DeepSeek V4 Pro, Kimi K3 · 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 Kimi K3?
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 · GPT-5.3-Codex vs Kimi K3 · DeepSeek V4 Pro vs GPT-5.6 Sol · GPT-5.6 Sol vs Kimi K3 · DeepSeek V4 Pro vs GPT-5.5 · GPT-5.5 vs Kimi K3
Full ranking: Best AI for writing emails · model pages: DeepSeek V4 Pro, Kimi K3