GPT-6 Luna

• 📏 1.05M-token context: 922K input, 128K output
• ⚡ OpenAI's most efficient GPT-6 tier for high-volume work
• 👁️ Accepts text and image input, returns text
• 🔧 Function calling, web search, Responses API tools
• 🧠 Selectable reasoning effort from none up to max
• 🆕 Successor to GPT-5.6 Luna, launched alongside GPT-6 Sol
• 💬 Aimed at chat, classification, lightweight agentic workflows
• 🎯 Served via Responses and Chat Completions APIs

OpenAI

OpenAI is an American artificial intelligence research organization headquartered in San Francisco, structured as both a for-profit public benefit corporation and a nonprofit foundation. The lab developed the GPT family of large language models, the DALL-E…

GPT-6 Luna is the smallest, most cost-efficient member of OpenAI's GPT-6 lineup, released in September 2026 alongside GPT-6 Sol and sitting below the flagship GPT-6 Astra. OpenAI's own model guidance positions it for cost-sensitive, high-volume workloads, while Sol balances intelligence and cost and Astra handles the most complex reasoning and coding. It accepts text and images, emits text, and exposes a 1.05 million-token context window with up to 128K output tokens.

Compared with its direct predecessor, GPT-5.6 Luna, the continuity is notable: both share the same 1.05M-token window and the same selectable reasoning-effort ladder running from none through low, medium, high and max, plus vision input, function calling and hosted tools such as web search. The GPT-6 release refreshes this efficiency tier within the newer generation, so the same integration surface — Responses and Chat Completions — carries over for existing 5.6 Luna deployments.

Practically, Luna suits classification, extraction, routing, retrieval over very long documents, and focused agent steps, with reasoning effort dialled up when a task needs more deliberation and dialled down for latency-sensitive, high-throughput traffic. Teams needing deeper multi-step reasoning or heavier coding work are pointed by OpenAI's documentation toward Sol or Astra instead, keeping Luna as the volume workhorse of the family.