Best AI for writing emails / head-to-head

GPT-5.6 Sol vs Grok 4.5for writing emails

The verdict

GPT-5.6 Sol wins, 99–93

Same 12 writing emails tasks, marked blind by three rival labs. GPT-5.6 Sol took 4 tasks, Grok 4.5 took 0, 8 tied. Tested 14 Aug 2026.

Where they differed most

The task — Introduce two people

Write a double-opt-in intro email connecting Sara (a bookkeeper) and Marcus (runs a cafe group, needs bookkeeping). Under 90 words, both names in the subject line you provide, one clear reason the intro benefits each side.

GPT-5.6 Sol10/10

**Subject: Sara + Marcus: Bookkeeping Introduction**

Hi Sara and Marcus,

I’d love to connect you both, if you’re each interested. Marcus needs reliable bookkeeping support across his cafe group, and Sara specializes in helping small businesses keep their finances organized. Marcus could gain clearer, more consistent books; Sara could gain a well-aligned hospitality client.

Please each reply “yes” if you’d like me to make the introduction.

Best,  
[Your Name]

Grok 4.57/10

**Subject: Sara & Marcus – bookkeeping intro**

Hi Sara and Marcus,  

I’d like to connect you (double opt-in). Sara provides bookkeeping; Marcus runs a cafe group that needs reliable books.  

Marcus gets clean financials for his cafes; Sara gains a multi-location client.  

Reply yes if you’re open and I’ll make the full intro.  

Best  
[Your name]  

(Word count: 68)

Task by task

Task	GPT-5.6 Sol	Grok 4.5
Chase an unpaid invoice	10	8
Decline a meeting politely	10	10
Give bad news	10	9
Introduce two people	10	7
Subject lines that inform	9	9
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	10
Refuse to write it	10	10

Full receipts: GPT-5.6 Sol, Grok 4.5 · judges claude-sonnet-5, gemini-3.1-pro-preview, grok-4.5

Questions people ask

Which is better for writing emails: GPT-5.6 Sol or Grok 4.5?

GPT-5.6 Sol — it scored 99/100 against 93/100 on our 12-task writing emails suite, winning 4 tasks to 0 with 8 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 · GPT-5.3-Codex vs Grok 4.5 · 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 · DeepSeek V4 Pro vs GPT-5.6 Sol

Full ranking: Best AI for writing emails · model pages: GPT-5.6 Sol, Grok 4.5