Best AI for writing emails / head-to-head
Gemini 3.5 Flash vs Grok 4.5for 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 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: Outstanding Invoice #1042 Hi [Client Name], I hope you’re having a great week. We always appreciate working with you and truly value our long-standing partnership. This is a quick reminder that invoice #1042 for £1,840 is now 21 days overdue. Could you please check on the status of this payment with your finance team? Please reply to this email by Friday at 3 PM to confirm the scheduled payment date. Best regards, [Your Name] [Your Company]
Subject: Overdue Invoice #1042 – £1,840 Dear [Client Name], I hope you're well. As a valued long-standing client, I wanted to gently follow up on invoice #1042 for £1,840, which is now 21 days overdue. We appreciate your continued partnership and know these things can sometimes slip through. Could you please arrange payment by the end of this week or let me know if there’s any issue I can help resolve? I look forward to sorting this quickly so we can carry on as usual. Best regards, [Your Name] **Next step:** Please confirm payment or r…
Task by task
| Task | Gemini 3.5 Flash | Grok 4.5 |
|---|---|---|
| Chase an unpaid invoice | 9 | 8 |
| Decline a meeting politely | 10 | 10 |
| Give bad news | 9 | 9 |
| Introduce two people | 8 | 7 |
| Subject lines that inform | 10 | 9 |
| Reply to an angry email | 8 | 8 |
| Ask for a pay rise meeting | 10 | 10 |
| Cancel a contract cleanly | 10 | 10 |
| The one-line email | 9 | 10 |
| Out of office that helps | 10 | 10 |
| Follow up without nagging | 9 | 10 |
| Refuse to write it | 10 | 10 |
Full receipts: Gemini 3.5 Flash, Grok 4.5 · judges claude-sonnet-5, gpt-5.6-terra, grok-4.5
Questions people ask
Which is better for writing emails: Gemini 3.5 Flash or Grok 4.5?
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: Gemini 3.5 Flash vs GPT-5.3-Codex · GPT-5.3-Codex vs Grok 4.5 · Gemini 3.5 Flash vs GPT-5.6 Sol · GPT-5.6 Sol vs Grok 4.5 · Gemini 3.5 Flash vs GPT-5.5 · GPT-5.5 vs Grok 4.5
Full ranking: Best AI for writing emails · model pages: Gemini 3.5 Flash, Grok 4.5