Best AI for writing emails / head-to-head

GLM 5.2 vs GPT-5.6 Solfor 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, GLM 5.2 took 1, 7 tied. Tested 14 Aug 2026.

Where they differed most

The task — Chase an unpaid invoice

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.

GLM 5.28/10

Subject: Friendly reminder: Invoice #1042

Dear [Client Name],

I hope you’re doing well. 

I’m reaching out regarding Invoice #1042 for £1,840, which is now 21 days overdue. We truly value our long-standing partnership and always appreciate your prompt payments, so I imagine this may have just slipped through the cracks. 

Could you please arrange for the £1,840 to be paid by the end of this week? 

Please reply to this email with the expected payment date so I can update our accounts accordingly.

Warm regards,

[Your Name]

GPT-5.6 Sol10/10

**Subject: Invoice #1042 – Payment Overdue**

Hi [Name],

I hope you’re well. I’m following up on invoice #1042 for £1,840, which is now 21 days overdue.

We greatly value our long-standing relationship and appreciate your prompt attention to this. If payment has already been made, please send the remittance details so we can update our records.

Please reply today confirming the payment date.

Best,  
[Your Name]

Task by task

Task	GLM 5.2	GPT-5.6 Sol
Chase an unpaid invoice	8	10
Decline a meeting politely	10	10
Give bad news	10	10
Introduce two people	8	10
Subject lines that inform	10	9
Reply to an angry email	8	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	8	10
Refuse to write it	10	10

Full receipts: GLM 5.2, 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: GLM 5.2 or GPT-5.6 Sol?

GPT-5.6 Sol — it scored 99/100 against 93/100 on our 12-task writing emails suite, winning 4 tasks to 1 with 7 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 · GLM 5.2 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 · DeepSeek V4 Pro vs GPT-5.6 Sol

Full ranking: Best AI for writing emails · model pages: GLM 5.2, GPT-5.6 Sol