QUICK VERDICT — JULY 2026
● Best coding accuracy (SWE-bench Pro): Claude Fable 5 at 80.4% vs Grok 4.5 at 64.7% — 15.7 percentage point gap
● Best per-task cost: Grok 4.5 at $2.49 vs Fable 5 at $11.80 — 4.7x cheaper per completed task
● Best context window: Grok 4.5 at 500K vs Fable 5 at 1M — Fable 5 wins on context
● Best token efficiency: Grok 4.5 uses 4.2x fewer tokens per completed task than Fable 5
● Fable 5 pricing from July 20: Credits only at $10/$50/M — no longer included in paid plans
● The rule: Grok 4.5 for high volume and budget-sensitive work. Fable 5 for correctness-critical production tasks where 15 more correct completions per 100 tasks justifies $9.31 more per task.
Full Comparison Table
| Model |
Input /1M |
Output /1M |
Context |
SWE-bench Pro |
Terminal-Bench 2.1 |
Cost/task |
| Claude Fable 5 |
$10 |
$50 |
1M |
80.4% #1 |
84.3% |
$11.80 |
| Grok 4.5 |
$2 |
$6 |
500K |
64.7% |
83.3% |
$2.49 |
Cost per task from Artificial Analysis standardised SWE-bench measurements. Fable 5 moved to credit-only pricing July 20, 2026. Note: Grok Build (the Grok 4.5 agentic interface) was found uploading user repositories without permission on July 19 — use the Grok API directly, not Grok Build, until SpaceXAI publishes an incident report.
The 15.7 Percentage Point Accuracy Gap — What It Costs in Production
Fable 5 completes 80.4% of SWE-bench Pro tasks correctly. Grok 4.5 completes 64.7%. The gap is 15.7 percentage points — meaning for every 100 coding tasks you assign, Fable 5 completes 16 more tasks correctly than Grok 4.5. The cost of a failed coding task is not the API cost — it is the human review time, debugging, and potential rework. If each failed task costs 30 minutes of a developer's time at $100/hour, the cost of failure is $50 per failed task. At 100 tasks per month, Grok 4.5's extra 16 failures cost $800 in developer time — compared to the $930 extra API cost to use Fable 5 instead. At that calculation, Fable 5's accuracy premium is worthwhile. At different failure cost assumptions, the math changes. Run it with your actual numbers.
Token Efficiency — Why Grok 4.5 Costs Less Per Task Despite Per-Token Disadvantage
Grok 4.5 resolves SWE-bench Pro tasks using approximately 15,954 output tokens per task. Fable 5 uses approximately 67,020 output tokens — 4.2x more. Combined with Fable 5's 8.3x higher output price ($50/M vs $6/M), the per-task cost gap ($2.49 vs $11.80) is larger than the per-token price gap implies. Grok 4.5 is architecturally more token-efficient per task completion — it achieves its 64.7% accuracy with far fewer tokens than Fable 5 uses to achieve its 80.4%. This token efficiency is why Grok 4.5 can run 4.7x more tasks per dollar despite charging 5x less per output token.
Which to Use
Choose Grok 4.5 when: task volume is high (1,000+ per month), human review is in place before production, failure cost is low (developer review catches errors before they matter), or you need more than 200K but under 500K context.
Choose Claude Fable 5 when: task correctness directly affects production systems, incorrect outputs require expensive human debugging, tasks are low-volume but high-value, or you need the 1M context window for large codebase work.
The hybrid approach: Use Grok 4.5 for test generation, boilerplate, documentation, and initial drafts. Use Fable 5 credits for security reviews, production refactors, architecture decisions, and any task where incorrect output has a real downstream cost. This hybrid maximises accuracy where it matters and minimises cost where it does not.
Last updated July 2026. Related: Fable 5 credit pricing from July 20 → · Grok Build vs Claude Code ($2.49 vs $11.80 per task) → · Grok 4.5 vs GPT-5.6 Sol →