Best Foundation Models for GPT-5.1-Codex

GPT-5.6 Luna is OpenAI’s fast, cost-efficient model in the GPT-5.6 lineup. The GPT-5.6 family includes Sol for flagship performance, Terra for balanced everyday work, and Luna for strong capability at the lowest listed price. Luna is designed for users who need scalable AI support for routine tasks, coding assistance, workflow automation, analysis, and production API use cases where speed and cost matter. According to the pasted preview text, Luna is priced below both Sol and Terra, making it the most affordable GPT-5.6 option for high-volume workloads. The model is included in GPT-5.6 benchmark previews across Terminal-Bench 2.1, GeneBench v1, ExploitBench, and ExploitGym, showing that it is part of the same technical family used for coding, biology, and cybersecurity evaluations. Luna benefits from safeguards developed across the GPT-5.6 series, including model-level refusal training, real-time cyber and biology misuse classifiers, account-level signals, differentiated access, monitoring, enforcement, and ongoing testing. These controls are designed to preserve legitimate use cases such as debugging, code review, defensive testing, security education, and productivity automation while constraining prohibited misuse. GPT-5.6 Luna is planned for broader access through ChatGPT, Codex, and the API after the limited preview period. GPT-5.6 Luna helps developers and organizations run useful AI workflows with a practical balance of affordability, responsiveness, and safety.

GPT-5.6 Terra is OpenAI’s balanced GPT-5.6 model for users who need strong performance across everyday work, development tasks, enterprise workflows, and technical analysis. The model is part of the GPT-5.6 family alongside Sol and Luna, with Terra positioned as the middle tier for capable, cost-efficient use. Terra is described as having competitive performance to GPT-5.5 while being 2x cheaper, making it useful for teams that want advanced capability without always using the flagship model. It supports coding workflows, agentic tasks, cybersecurity-related defensive work, biology workflows, knowledge work, and tool-assisted automation. In benchmark previews, Terra appears alongside Sol and Luna in evaluations for coding, biology, ExploitBench, and ExploitGym. The model benefits from the GPT-5.6 safeguard stack, which includes model-level refusals for prohibited cyber assistance, real-time cyber and biology misuse classifiers, and account-level risk review. These safeguards are designed to preserve access to legitimate work such as code review, debugging, vulnerability research, patch development, security education, and defensive testing. GPT-5.6 Terra is planned for availability through the API, Codex, and broader OpenAI products after the limited preview period. GPT-5.6 Terra helps teams get a balanced model for high-quality AI work when they need strong reasoning and automation at a lower cost than Sol.

GPT-6 is an upcoming OpenAI model and the expected next major step beyond the GPT-5.x generation. OpenAI has not yet announced GPT-6 as a generally available product, and public documentation does not currently include GPT-6 pricing, benchmarks, model cards, API access, context length, modality details, or release timing. The latest official OpenAI model materials instead focus on GPT-5.6 Sol, Terra, and Luna, with Sol positioned as the flagship model for complex reasoning and coding. GPT-6 should therefore be described as a forthcoming model rather than a current production option. If it follows OpenAI’s current roadmap direction, GPT-6 will likely improve performance across reasoning, software engineering, scientific work, enterprise workflows, multimodal tasks, and AI agents. It may also expand capabilities around tool use, computer use, file search, web search, long-context work, structured outputs, and high-reliability automation. For businesses, GPT-6 could eventually become a foundation for customer support agents, internal copilots, coding systems, data analysis workflows, research assistants, and complex knowledge-work automation. Developers should continue using officially documented OpenAI models until GPT-6 is formally released. By positioning GPT-6 as an upcoming model, organizations can discuss the future of OpenAI’s model family without overstating what is currently public.