OpenAI's new flagship GPT-5.6 Sol claims a lead over Anthropic's Claude Mythos in agentic coding and goes toe to toe with it in cybersecurity. Access stays limited to a handful of partners for now.
OpenAI has unveiled GPT-5.6 Sol, a new generation of models built to compete with Claude's Mythos class. The limited preview is only open to select partners through the API and Codex, at the explicit direction of the US government. 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."
GPT-5.6 also brings a new layered naming scheme that looks a lot like Claude's. The number (x.6) marks the generation, while Sol, Terra, and Luna are permanent performance tiers that can evolve on their own. 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.
