OpenAI: GPT-5.6 Luna

GPT-5.6 Luna is a fast, cost-efficient model in OpenAI's GPT-5.6 series. It is suited for high-volume, latency-sensitive tasks such as chat, classification, and lightweight agentic workflows, providing capable reasoning for its price tier.

The GPT-5.6 Luna documentation on OpenRouter includes the GPT-5.6 Migration Guide cookbook and the GPT 5.6 Discounts & Jevons Paradox blog post. The quickstart covers API keys and your first request, and the API reference lists every parameter.

GPT-5.6 Luna costs $0.20/M input tokens and $1.20/M output tokens, with separate rates for Cache Read at $0.02/M tokens, Cache Write at $0.25/M tokens, and Web Search at $10.00/1K calls.

GPT-5.6 Luna has a 1,050,000 token context window. It supports up to 128,000 completion tokens.

Yes. GPT-5.6 Luna accepts tools and tool_choice for function calling. It also supports structured outputs via a JSON schema in response_format.

Yes. OpenAI caches prompts of 1024 tokens or more automatically, and GPT-5.6 Luna bills a cache write on each cached prompt whether or not the cached prefix is read again. To turn caching off for a request, set prompt_cache_options.mode to "explicit" at the request root and do not mark any content block with prompt_cache_breakpoint. Explicit mode disables OpenAI-managed breakpoints, so a request with none of your own has no cacheable prefix and is billed at the plain input rate. See the prompt caching guide.

GPT-5.6 Luna accepts files such as PDFs, images, and text as input and returns text.

GPT-5.6 Luna is served by 3 providers on OpenRouter: OpenAI, Azure, and Amazon Bedrock. Requests are routed to the best available provider, with automatic failover to the others, and you can pin or exclude providers with provider routing.

GPT-5.6 Luna was released on July 9, 2026. Its knowledge cutoff is February 16, 2026.