OpenAI's GPT-5.6 Sol beats Anthropic's Claude Mythos 5 in agentic coding benchmarks, but the US government restricts access to select partners. OpenAI calls the policy unsustainable for developers and enterprises.
Key facts
- GPT-5.6 Sol scores 88.8% on Terminal-Bench 2.1.
- Sol Ultra hits 91.9% vs Claude Mythos 5's 88%.
- Sol uses one-third the tokens of Mythos Preview on ExploitBench.
- US government restricts access to select partners only.
- OpenAI calls the policy unsustainable for developers.
OpenAI has unveiled GPT-5.6 Sol, a new flagship model that claims a lead over Anthropic's Claude Mythos 5 in agentic coding and matches it in cybersecurity. The limited preview is only open to select partners through the API and Codex, at the explicit direction of the US government According to The Decoder. The same government previously yanked Anthropic's Mythos-class model Fable 5 off the market.
OpenAI isn't subtle about its frustration. "We don't believe this kind of government access process should become the long-term default. It keeps the best tools from users, developers, enterprises, cyber defenders, and global partners who need them."
The Model Family and Naming Strategy
GPT-5.6 introduces a layered naming scheme that mirrors Claude's. The number (x.6) marks the generation, while Sol, Terra, and Luna are permanent performance tiers that can evolve independently. Sol is the flagship. Terra matches GPT-5.5 at half the cost. Luna is the budget option. On top of that, there's a "max" mode for deeper reasoning and an "ultra" mode that farms out complex tasks to sub-agents running in parallel.
Benchmark Results: Sol vs. Mythos 5
OpenAI's benchmark numbers put Sol ahead of Anthropic's Claude Mythos 5 in agentic coding. On Terminal-Bench 2.1, Sol scores 88.8 percent. Sol Ultra hits 91.9, Claude Mythos 5 lands at 88 percent, and Fable 5 trails at 84.3. Sol also shows gains in biology. On GeneBench v1, a benchmark for genomics and quantitative biology, it beats GPT-5.5 (30 percent vs. 22 percent best case) while burning fewer tokens.
On ExploitBench, which tests how well AI agents can find and exploit real security flaws in Google's V8 JavaScript engine all the way to full code execution, Sol matches Mythos Preview's performance while using roughly a third of the output tokens, OpenAI says. On ExploitGym, a benchmark built by UC Berkeley researchers with OpenAI and other labs, all three GPT-5.6 models get better as reasoning effort goes up. That points to room for scaling with more compute. Claude numbers for this benchmark aren't available yet.
The Government Access Dilemma
The US government's restriction on GPT-5.6 Sol mirrors the earlier suspension of Anthropic's Fable 5. OpenAI is publicly pushing back, arguing that the policy hurts developers and businesses. Meanwhile, new models launching in Asia promise Mythos-like capabilities without fear of an export ban. As previously reported, U.S. AI labs may never recover this enormous market [TechCrunch reports].
Unique Take: The Government Gating Is a Feature, Not a Bug
While OpenAI frames the government restriction as an obstacle, it may inadvertently serve as a marketing signal. By restricting access to select partners, OpenAI creates an aura of exclusivity and safety, potentially driving demand when broader access eventually comes. This mirrors the playbook used by Anthropic with Mythos 5, which was also gated before wider release. The real test will be whether OpenAI can maintain benchmark leadership while navigating regulatory constraints that its Asian competitors don't face.
What to watch
Watch for OpenAI's Q3 2026 developer conference, where broader access to GPT-5.6 Sol may be announced. Also monitor the US government's response to OpenAI's criticism and whether Asian competitors like DeepSeek capture market share with unrestricted models.
Source: the-decoder.com
