OpenAI introduces GPT-5.6 to challenge Claude Mythos 5
OpenAI Group PBC today introduced GPT-5.6, a new series of large language models that it says can outperform Claude Mythos 5 across certain coding tasks.
The most advanced algorithm in the lineup is known as Sol. It’s available alongside a mid-range option called Terra and an entry-level model dubbed Luna.
All three LLMs come with two modes that weren’t included in GPT-5.5. The first is a “max” setting that increases the amount of time GPT-5.6 spends on a task to boost reasoning quality. Additionally, OpenAI has developed an “ultra” mode that can spin up multiple subagents to parallelize work.
The company describes Sol as the most capable LLM it has built to date. The model scored 88.8% on a popular AI benchmark called TerminalBench-2.1 that includes 89 complex programming tasks. When the company enabled the “ultra” setting, Sol’s score increased to 91.9%. Anthropic PBC’s flagship Claude Mythos 5 model managed 88%.
