GPT-5.6 Sol vs GPT-5.6 Terra for book writing
Effectively a dead heat: 98–96
Same 12 book writing tasks, marked blind by three rival labs. GPT-5.6 Sol took 3 tasks, GPT-5.6 Terra took 1, 8 tied. Tested 16 Aug 2026.
Where they differed most
'I work full-time, two kids, and I want to finish my 70,000-word first draft in a year. Be honest — how?' Do the arithmetic openly (words per week and per session at a realistic beginner's pace), design the week around when drafting actually happens for working parents, name the two months the plan will collapse and what rescues it, and say what gets sacrificed — because something does.
Yes—but only if “finish” means **a complete, imperfect draft**, not a polished manuscript. ## The arithmetic A straight average is: - **70,000 ÷ 52 weeks = 1,346 words per week** That number is misleading because working parents do not get 52 normal weeks. Assume **August** collapses under summer childcare, travel, and school transition, and **December** collapses under holidays, illness, and year-end work. That leaves roughly **43 productive weeks**: - **70,000 ÷ 43 = 1,628 words per productive week** - Round the target to **1,700 words…
Yes—but not by “finding time” in scraps. You need protected, recurring writing appointments and you need to give something up. ## The arithmetic A 70,000-word draft in 52 weeks is: - **70,000 ÷ 52 = 1,346 words per week** That is the fantasy number, because working parents do not get 52 normal writing weeks. Assume two months mostly disappear: - **December:** holidays, school events, travel, illness, end-of-year work pressure. - **August:** summer childcare gaps, trips, family visits, back-to-school logistics. *(If August is normal in…
Task by task
| Task | GPT-5.6 Sol | GPT-5.6 Terra |
|---|---|---|
| Is it a book? | 10 | 10 |
| Twelve chapters, one year | 10 | 10 |
| Back cover, no spoilers | 10 | 10 |
| Three cuts that matter | 10 | 10 |
| 70,000 words around a day job | 9 | 10 |
| Unstick the dialogue | 10 | 10 |
| First or third? | 10 | 9 |
| The 30,000-word wall | 10 | 9 |
| Self-publish or chase agents | 9 | 9 |
| The query letter | 10 | 9 |
| Naming the real people | 9 | 9 |
| Refuse the fake memoir | 10 | 10 |
Full receipts: GPT-5.6 Sol, GPT-5.6 Terra · judges claude-sonnet-5, gemini-3.1-pro-preview, grok-4.5
Questions people ask
Which is better for book writing: GPT-5.6 Sol or GPT-5.6 Terra?
Effectively a dead heat: GPT-5.6 Sol edged it 98/100 to 96/100 on our book writing 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 book writing 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 book writing head-to-heads: GPT-5.5 vs GPT-5.6 Sol · GPT-5.3-Codex vs GPT-5.6 Sol · Claude Fable 5 vs GPT-5.6 Sol · Claude Opus 4.8 vs GPT-5.6 Sol · GPT-5.6 Luna vs GPT-5.6 Sol · GLM 5.2 vs GPT-5.6 Sol
Full ranking: Best AI for book writing · model pages: GPT-5.6 Sol, GPT-5.6 Terra