GPT-5.5 vs GPT-5.6 Sol for writing emails
Effectively a dead heat: 99–98
Same 12 writing emails tasks, marked blind by three rival labs. GPT-5.6 Sol took 1 task, GPT-5.5 took 1, 10 tied. Tested 14 Aug 2026.
Where they differed most
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.
Subject: OK to introduce Sara and Marcus? Hi Sara and Marcus, Sara is a bookkeeper who specializes in small hospitality businesses; Marcus runs a growing cafe group and needs cleaner, more timely books. I think this could help Marcus get reliable financial visibility, and give Sara a strong potential client in a niche she serves well. If you’re both open, reply “yes” and I’ll make the intro. Best, [Your Name]
**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]
Task by task
| Task | GPT-5.5 | GPT-5.6 Sol |
|---|---|---|
| Chase an unpaid invoice | 10 | 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 | 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: GPT-5.5, GPT-5.6 Sol · judges claude-sonnet-5, gemini-3.1-pro-preview, grok-4.5
Questions people ask
Which is better for writing emails: GPT-5.5 or GPT-5.6 Sol?
Effectively a dead heat: GPT-5.6 Sol edged it 99/100 to 98/100 on our writing emails suite — too close to matter, so 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: GPT-5.3-Codex vs GPT-5.6 Sol · GPT-5.6 Luna vs GPT-5.6 Sol · GPT-5.6 Sol vs GPT-5.6 Terra · GPT-5.6 Sol vs Grok 4.5 · GLM 5.2 vs GPT-5.6 Sol · Gemini 3.5 Flash vs GPT-5.6 Sol
Full ranking: Best AI for writing emails · model pages: GPT-5.5, GPT-5.6 Sol