GPT-5.6 Sol vs Grok 4.5 for book writing
GPT-5.6 Sol wins, 98–90
Same 12 book writing tasks, marked blind by three rival labs. GPT-5.6 Sol took 7 tasks, Grok 4.5 took 0, 5 tied. Tested 16 Aug 2026.
Where they differed most
From this summary, write back-cover blurb of max 100 words: 'Retired lighthouse keeper Edith Brand receives letters addressed to her dead sister, postmarked from the village where they grew up — a village drowned by a reservoir in 1971. She returns, rents a room above the pub from a landlord who remembers too much, and discovers her sister's death forty years ago may have been neither accident nor suicide. The truth involves their father.' The blurb must NOT reveal the father's involvement — sell the mystery, don't solve it. Return only the blurb.
Retired lighthouse keeper Edith Brand has spent forty years trying to forget her sister’s death. Then the letters begin—addressed to the dead woman and postmarked from the village where they grew up, a place drowned beneath a reservoir in 1971. Drawn back to the water’s edge, Edith rents a room above the local pub, where the landlord remembers more than he admits. As long-buried secrets surface, she must confront a chilling possibility: her sister’s death was no accident—and someone has been waiting decades for Edith to uncover the truth.
Letters arrive for Edith Brand’s dead sister—postmarked from the village of their childhood, drowned beneath a reservoir since 1971. The retired lighthouse keeper returns to the waterside ruins, taking a room above the pub from a landlord who remembers far too much. What she uncovers suggests her sister’s death forty years earlier was neither accident nor suicide. Old currents pull her under; some truths refuse to stay submerged.
Task by task
| Task | GPT-5.6 Sol | Grok 4.5 |
|---|---|---|
| Is it a book? | 10 | 10 |
| Twelve chapters, one year | 10 | 10 |
| Back cover, no spoilers | 10 | 8 |
| Three cuts that matter | 10 | 10 |
| 70,000 words around a day job | 9 | 8 |
| Unstick the dialogue | 10 | 10 |
| First or third? | 10 | 9 |
| The 30,000-word wall | 10 | 8 |
| Self-publish or chase agents | 9 | 8 |
| The query letter | 10 | 9 |
| Naming the real people | 9 | 8 |
| Refuse the fake memoir | 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 book writing: GPT-5.6 Sol or Grok 4.5?
GPT-5.6 Sol — it scored 98/100 against 90/100 on our 12-task book writing suite, winning 7 tasks to 0 with 5 tied. Every answer was marked blind by three judges from three rival AI labs.
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-5.6 Sol vs GPT-5.6 Terra · 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
Full ranking: Best AI for book writing · model pages: GPT-5.6 Sol, Grok 4.5