Our Verdict
GPT-5.6 Sol wins
GPT-5.6 Sol wins the overall comparison due to its superior benchmark performance on Terminal-Bench 2.1 (88.8% vs 84.3%), significantly lower pricing ($5/$30 vs $10/$50 per million tokens), and the innovative Ultra mode that uses subagents for parallel processing. While Mythos 5 is exceptional for deep reasoning and cybersecurity, Sol offers better value across a broader range of applications.
The AI world changed on June 26, 2026 when OpenAI unveiled GPT-5.6 Sol and the US government simultaneously authorized Anthropic to release Claude Mythos 5 to trusted partners. Both models represent the cutting edge of AI capability, but they excel in different areas. GPT-5.6 Sol leads on agentic coding benchmarks, efficiency, and cost-effectiveness, while Claude Mythos 5 excels in deep reasoning, cybersecurity, and autonomous long-horizon tasks. The choice between them depends on your specific use case, budget, and access requirements.
Every category compared head-to-head. Check marks indicate the winner in each category.
| Category | GPT-5.6 Sol | Claude Mythos 5 | Winner |
|---|---|---|---|
| Terminal-Bench 2.1 | 88.8% (91.9% Ultra) | 84.3% | |
| SWE-Bench Verified | ~80% | 80.8% | |
| SWE-Bench Pro | ~64% | 69.2% | |
| Cybersecurity (ExploitBench) | Competitive, 1/3 tokens | Strong (Mythos Preview: 10K+ vulns) | |
| API Price (per 1M input) | $5 | $10 | |
| API Price (per 1M output) | $30 | $50 | |
| Subagent / Ultra Mode | Yes (Ultra mode) | No | |
| Max Reasoning Effort | Yes (max setting) | Yes (extended thinking) | |
| Government Restrictions | Limited preview, GA soon | Trusted partners only | |
| Context Window | 128K tokens | 200K tokens | |
| Autonomous Task Length | Good for multi-step | Excellent, hours-long | |
| Current Availability | Limited API/Codex preview | 100+ trusted partners |
For terminal/agentic coding, Sol leads (88.8% vs 84.3% on Terminal-Bench 2.1). For software engineering tasks, Mythos 5 leads on SWE-Bench Pro (69.2% vs ~64%). The choice depends on whether you need autonomous agentic work or deep codebase understanding.
GPT-5.6 Sol is significantly cheaper at $5/$30 per million tokens vs Mythos 5's $10/$50. For budget-conscious deployments, GPT-5.6 Luna at $1/$6 offers competitive performance at a fraction of the cost.
GPT-5.6 Sol is in limited preview for trusted partners through API and Codex. Claude Mythos 5 is available to 100+ trusted partners. Both companies plan broader availability in the coming weeks.
The government has become an active gatekeeper for frontier AI. OpenAI coordinated its launch with the government voluntarily, while Anthropic's models were restricted under export control. Future releases will likely involve ongoing government oversight.
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