GPT-5.6 Sol vs Claude Fable 5.1: Agentic Coding, Cost & Capability (2026)
GPT-5.6 Sol vs Claude Fable 5 (2026): Sol leads the AA Coding Agent Index at half the price; Ramp billing data shows Fable 5 at only 8% of production model spend.
September 2026 reset the board: GPT-6 Astra launched at Fable 5.1's list price ($10/$50), ties GPT-5.6 Sol on the Artificial Analysis Intelligence Index (61), and Claude Fable 5.1 defends the crown at 66. The old logic of this page now holds sharper than before: if raw intelligence, research depth and long-horizon judgment decide your task, the Fable line remains the reference; if cost per solved task inside an agent loop decides your budget, the OpenAI line (Sol today, Astra from this week) measurably offers more frontier per dollar. One warning now applies to both camps: headline scores increasingly belong to the harness — ARC-AGI-3 showed 62.7% vs 99.9% for the same model. Test on your own workloads, not on launch-day tables.
Detailed Comparison
A side-by-side analysis of key factors to help you make the right choice.
| Factor | GPT-5.6 SolRecommended | Claude Fable 5 | Winner |
|---|---|---|---|
| Agentic coding throughput (AA Coding Agent Index) | Leads: 80 in Codex, top score in all three sub-evals (DeepSWE, Terminal-Bench v2, SWE-Atlas-QnA) | 77.2 in Claude Code (max reasoning) | |
| Peak raw intelligence (AA Intelligence Index v4.1) | 58.9 (Sol max) — one point behind | 59.9 (max) — highest of any model | |
| Cost per solved task | ~1/3 the cost per Intelligence Index task ($1.04); ~40% cheaper per coding task | Baseline — highest cost per task of the frontier models | |
| Analytical & knowledge-work depth (AA-Briefcase) | Rubric 42%; Analytical Quality Elo 1592; highest Presentation Elo of any model | Leads: Rubric 56%; Analytical Quality Elo 1764 | |
| Output token efficiency | ~15k output tokens per Intelligence task; fewer than Opus 4.8 (max) while more intelligent | Higher token use per task at the top of the intelligence range | |
| Reliability & hallucination resistance | AA-Omniscience: small accuracy gain over GPT-5.5 but a higher hallucination rate | Higher rubric-graded analytical rigor on complex reasoning | |
| List price (per million input/output tokens) | $5 / $30, plus new cache-write pricing (1.25x input) and a 90% cache-read discount | $10 / $50 — roughly double the input and output rates | |
| Economically valuable task completion (GDPval-AA v2) | Elo 1,747.8 — 'similar ability to complete economically valuable tasks' | Elo 1,759.6 — marginally ahead | |
| The Astra shock (September 2026) | GPT-6 Astra (2026-09-03) lists at exactly Fable 5.1's price ($10/$50) and ties Sol on the Artificial Analysis Intelligence Index (61) while keeping the per-task cost edge — OpenAI closed the price gap without overtaking Fable. | Claude Fable 5.1 keeps the intelligence crown (AA Index 66), but its old argument — being the only frontier model in its price tier — is gone; switching now costs nothing, so the decision has become a harness question. | |
| Total Score | 4/ 9 | 3/ 9 | 2 ties |
Key Statistics
Real data from verified industry sources to support your decision.
Artificial Analysis
Artificial Analysis
Artificial Analysis
Artificial Analysis / Anthropic
Artificial Analysis
Artificial Analysis
DigitalApplied (citing OpenAI GA page)
FT / Ramp AI Index (via Simon Willison)
FT / Ramp AI Index (via Simon Willison)
OpenAI — GPT-6 Astra launch post
Simon Willison / Artificial Analysis
ARC Prize
All statistics come from verified third-party sources. Source, year, and direct link are shown on each metric.
When to Choose Each Option
Clear guidance based on your specific situation and needs.
Choose GPT-5.6 Sol when...
- You run high-volume, unattended agentic coding where per-task cost compounds across thousands of runs
- Your workflow is built on Codex, or you want frontier-adjacent intelligence at roughly one third the cost
- Output-token and latency budgets matter, and you want the leading coding-agent score per dollar
- You want a range of reasoning-effort tiers (Sol / Terra / Luna) to tune cost against capability
Choose Claude Fable 5 when...
- You need the single highest raw intelligence and the deepest analytical, rubric-graded output
- Your work is heavy on SWE-Bench Pro-style engineering, GDPval tasks, or complex reasoning where hallucination is costly
- You are already invested in Claude Code and the analytical-quality gap justifies the higher price
- Output quality and knowledge-work depth matter more to you than cost per task or raw throughput
Our Recommendation
September 2026 reset the board: GPT-6 Astra launched at Fable 5.1's list price ($10/$50), ties GPT-5.6 Sol on the Artificial Analysis Intelligence Index (61), and Claude Fable 5.1 defends the crown at 66. The old logic of this page now holds sharper than before: if raw intelligence, research depth and long-horizon judgment decide your task, the Fable line remains the reference; if cost per solved task inside an agent loop decides your budget, the OpenAI line (Sol today, Astra from this week) measurably offers more frontier per dollar. One warning now applies to both camps: headline scores increasingly belong to the harness — ARC-AGI-3 showed 62.7% vs 99.9% for the same model. Test on your own workloads, not on launch-day tables.
Frequently Asked Questions
Common questions about this comparison answered.
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