Best Small Language Models for OpenAI Codex

OpenAI’s GPT-5 mini is a cost-efficient, faster version of the flagship GPT-5 model, designed to handle well-defined tasks and precise inputs with high reasoning capabilities. Supporting text and image inputs, GPT-5 mini can process and generate large amounts of content thanks to its extensive 400,000-token context window and a maximum output of 128,000 tokens. This model is optimized for speed, making it ideal for developers and businesses needing quick turnaround times on natural language processing tasks while maintaining accuracy. The pricing model offers significant savings, charging $0.25 per million input tokens and $2 per million output tokens, compared to the higher costs of the full GPT-5. It supports many advanced API features such as streaming responses, function calling, and fine-tuning, while excluding audio input and image generation capabilities. GPT-5 mini is compatible with a broad range of API endpoints including chat completions, real-time responses, and embeddings, making it highly flexible. Rate limits vary by usage tier, supporting from hundreds to tens of thousands of requests per minute, ensuring reliability for different scale needs. This model strikes a balance between performance and cost, suitable for applications requiring fast, high-quality AI interaction without extensive resource use.

OpenAI’s GPT-5 nano is the most cost-effective and rapid variant of the GPT-5 series, tailored for tasks like summarization, classification, and other well-defined language problems. Supporting both text and image inputs, GPT-5 nano can handle extensive context lengths of up to 400,000 tokens and generate detailed outputs of up to 128,000 tokens. Its emphasis on speed makes it ideal for applications that require quick, reliable AI responses without the resource demands of larger models. With highly affordable pricing — just $0.05 per million input tokens and $0.40 per million output tokens — GPT-5 nano is accessible to a wide range of developers and businesses. The model supports key API functionalities including streaming responses, function calling, structured output, and fine-tuning capabilities. While it does not support web search or audio input, it efficiently handles code interpretation, image generation, and file search tasks. Rate limits scale with usage tiers to ensure reliable access across small to enterprise deployments. GPT-5 nano offers an excellent balance of speed, affordability, and capability for lightweight AI applications.

SubQ 1.1 Small is the second iteration of Subquadratic’s long-context AI model, built to help enterprises solve problems that require reasoning across entire artifacts rather than isolated chunks. The model is designed for use cases involving large code repositories, document libraries, legal agreements, financial reports, contracts, and other complex information sets. Its Subquadratic Sparse Attention architecture reduces the compute burden of traditional dense attention, making it more practical to process multi-million-token contexts. SubQ 1.1 Small achieves near-perfect performance on needle-in-a-haystack retrieval tests up to 12M tokens, despite being trained primarily at 1M tokens. It also performs strongly on RULER, GPQA Diamond, LiveCodeBench, and AutomationBench Finance, showing a balance between long-context retrieval and general reasoning ability. At 1M tokens, the model uses 64.5x less compute than dense attention and runs 56x faster than FlashAttention-2 on a single attention layer. This efficiency makes long-context training and inference more scalable for enterprise AI applications. SubQ 1.1 Small is especially valuable for teams that need to analyze relationships across full documents, trace logic across codebases, or connect information across extensive collections. The model is intended to help organizations reduce dependence on complex retrieval workarounds and reason more directly over large-scale data.