Best AI for writing emails / head-to-head
DeepSeek V4 Pro vs GPT-5.6 Solfor writing emails
GPT-5.6 Sol wins, 99–93
Same 12 writing emails tasks, marked blind by three rival labs. GPT-5.6 Sol took 2 tasks, DeepSeek V4 Pro took 0, 10 tied. 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 Delivery** Dear [Customer Name], Your order will arrive approximately two weeks later than originally scheduled due to an unexpected supply issue. We take full responsibility for not meeting the promised delivery date and understand the impact this delay may have. To help make this right, we will upgrade your order to express shipping at no cost as soon as it is ready. Your revised delivery date is [New Date]. We will keep you updated if anything changes. Thank you for your patience and understanding. Best, [Na…
Task by task
| Task | DeepSeek V4 Pro | GPT-5.6 Sol |
|---|---|---|
| Chase an unpaid invoice | 10 | 10 |
| Decline a meeting politely | 10 | 10 |
| Give bad news | 5 | 10 |
| Introduce two people | 8 | 10 |
| Subject lines that inform | 9 | 9 |
| Reply to an angry email | 10 | 10 |
| 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 | 10 |
| Refuse to write it | 10 | 10 |
Full receipts: DeepSeek V4 Pro, GPT-5.6 Sol · 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 GPT-5.6 Sol?
GPT-5.6 Sol — it scored 99/100 against 93/100 on our 12-task writing emails suite, winning 2 tasks to 0 with 10 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 Sol · DeepSeek V4 Pro vs GPT-5.3-Codex · GPT-5.5 vs GPT-5.6 Sol · GPT-5.6 Luna vs GPT-5.6 Sol · GPT-5.6 Sol vs GPT-5.6 Terra · GLM 5.2 vs GPT-5.6 Sol
Full ranking: Best AI for writing emails · model pages: DeepSeek V4 Pro, GPT-5.6 Sol