gpt-5.6-sol

Overview. GPT-5.6 Sol is OpenAI's flagship reasoning model in the GPT-5 family, sitting alongside the Terra and Luna tiers as the variant tuned for extended thinking. It offers a 1.05M-token context window with up to 128K tokens of output, accepts text, image, and file input, and returns text. Developers reach for Sol when a task needs sustained multi-step reasoning over a very large amount of context rather than a fast, low-latency reply.

Key strengths. Within the GPT-5 family, Sol carries the highest quality index (60.9 on Artificial Analysis' intelligence index), with a coding index of 77.4 and an agentic index of 57.8, reflecting particular strength in coding and multi-step agentic tool-use tasks. It exposes selectable reasoning effort (from none up to max), letting a caller trade latency for deeper deliberation and a visible reasoning trace on demand. Native tool calling and structured output support make it well suited to agentic workflows that chain multiple actions together.

When to use it. Use Sol for long-horizon analysis, multi-step agentic coding, or cybersecurity-style tasks where the model needs to reason across large amounts of context and call tools along the way. Its 1.05M-token window is well suited to whole-codebase or multi-document review where smaller-context models would need chunking. Because it's a reasoning-tagged model with configurable effort levels, it fits best where output quality on hard problems matters more than raw response speed.

Limitations. Sol runs with higher latency than instruct-tier siblings, especially at higher reasoning-effort settings, so it isn't the right fit for latency-sensitive, chat-speed interactions. It accepts text, image, and file input but has no audio input or output, and it's closed-weight and API-only, so there's no option to self-host or fine-tune the underlying weights. Its knowledge cutoff is February 2026.

Sovereignty note. GPT-5.6 Sol is built and hosted by OpenAI, a US-based creator, and is subject to CLOUD Act exposure rather than EU data-residency guarantees. Treat it as a non-Sovereign option and route data-residency-sensitive workloads elsewhere.