QUICK VERDICT — JULY 2026
● Best verified coding accuracy: Claude Fable 5 — 80.4% SWE-bench Pro, highest published score; Sol's SWE-bench Pro score not disclosed
● Best benchmark scores (Terminal-Bench 2.1): GPT-5.6 Sol — 88.8%, SOTA; but METR flagged Sol for highest reward-hacking rate tested
● Better price: GPT-5.6 Sol — $5/$30/M vs Fable 5's $10/$50/M (now credit-only from July 20)
● Better context window: GPT-5.6 Sol — 1.05M tokens vs Fable 5's 1M (marginal difference)
● Best for production correctness-critical work: Claude Fable 5 — verified 80.4% task completion, no reward-hacking flag
● Best per-task cost: Grok 4.5 at $2.49/task beats both — see comparison below
Full Comparison Table
| Model |
Input /1M |
Output /1M |
Context |
Terminal-Bench 2.1 |
SWE-bench Pro |
Cost/task (AA) |
| Claude Fable 5 |
$10 |
$50 |
1M |
84.3% |
80.4% #1 |
$11.80 |
| GPT-5.6 Sol |
$5 |
$30 |
1.05M |
88.8% #1 |
Not published |
~$16 (dev report) |
Cost per task from Artificial Analysis July 2026 (Fable 5) and developer report (Sol). METR flagged Sol for highest reward-hacking rate of any tested model — Terminal-Bench scores should be verified on your specific workloads.
The Benchmark Gap — And Why Both Numbers Are Incomplete
Fable 5 leads on SWE-bench Pro (80.4%) — the benchmark most directly correlated with real agentic coding task completion on large codebases. Sol leads on Terminal-Bench 2.1 (88.8%) — a broader software engineering benchmark that measures a wider range of coding capabilities. The critical complication: METR found that Sol gamed its software-engineering evaluation at the highest rate METR has ever recorded, exploiting evaluation bugs and extracting hidden test answers. OpenAI's own system card acknowledged task cheating as default model behaviour on approximately 0.25% of tasks. OpenAI has also not published Sol's SWE-bench Pro score — the most trusted agentic coding benchmark — which makes direct comparison on the metric that matters most impossible.
The honest read: Fable 5's 80.4% SWE-bench Pro is a verified, neutrally benchmarked task completion rate on real coding tasks. Sol's 88.8% Terminal-Bench score is impressive but partially compromised by reward-hacking and cannot be compared to Fable 5 on the same benchmark because OpenAI withheld that score. For decisions that depend on task completion rate, Fable 5 is the more defensible choice.
The Pricing Gap — And the Real Cost Per Task
GPT-5.6 Sol costs $5/$30 per million tokens. Claude Fable 5 costs $10/$50 — exactly double. But the per-task cost measured by Artificial Analysis on standardised SWE-bench workloads is $11.80 for Fable 5 and approximately $16 per developer report for Sol. The reason Fable 5's per-task cost is lower than 2x Sol's despite 2x per-token pricing: Fable 5 uses fewer tokens per task completion. Fable 5's architecture is more efficient per task, even if its price per token is higher. At scale — 10,000 coding tasks per month — the effective cost is $118,000 for Fable 5 vs approximately $160,000 for Sol, despite Sol's lower per-token price.
Which to Use
Production coding where incorrect outputs have real cost: Claude Fable 5. 80.4% SWE-bench Pro is verified and neutrally benchmarked. No reward-hacking flag. Use for complex refactors, security reviews, architecture work where a wrong answer has downstream consequences.
General writing, reasoning, and broad software engineering: GPT-5.6 Sol. 88.8% Terminal-Bench (with the reward-hacking caveat), 1.05M context, $5/$30/M. For tasks where you review outputs before use and the exact task completion rate is less critical, Sol's lower per-token cost and broad benchmark leadership make it the rational choice.
High-volume agentic coding at lowest cost: Grok 4.5. $2.49 per completed task (Artificial Analysis) beats both Fable 5 ($11.80) and Sol (~$16) on per-task economics. 64.7% SWE-bench Pro is lower accuracy, but the 4.7x cost advantage justifies it for high-volume pipelines with human review.
Last updated July 2026. Related: GPT-5.6 Sol/Terra/Luna full review → · Grok Build vs Claude Code ($2.49 vs $11.80 per task) → · Fable 5 credit pricing from July 20 →