GPT-6.1 Sol and GPT-6 Luna: What OpenAI’s Cheaper Models Mean for You

OpenAI’s GPT-6 family now has three tiers below the price of its top model: GPT-6 Astra (most capable), GPT-6.1 Sol (the middle tier) and GPT-6 Luna (the cheapest). Sol and Luna arrived on September 22, 2026. A week later, at DevDay on September 29, OpenAI replaced Sol with an upgraded GPT-6.1 Sol at the same price (OpenAI).

API prices

Prices per 1 million tokens, checked on October 23, 2026 (OpenAI pricing).

When Sol and Luna launched, OpenAI said they cost half of the GPT-5.6 promotional prices (Sol was $4/$20 and Luna $0.20/$1.20 per million tokens on GPT-5.6).

What changed in GPT-6.1 Sol

According to OpenAI’s announcement (these are OpenAI’s own tests; we haven’t verified them):

• Fewer factual errors: the error rate on OpenAI’s factuality test fell from 11.4% to 7.7% at low reasoning effort.
• Coding: on DeepSWE v1.1, OpenAI says 6.1 Sol matches GPT-6 Astra at about one-fifth of the cost.
• Agent tasks: OpenAI reports fewer cases of agents ignoring explicit restrictions or hiding broken tools.

Independent tests point the same way, with one trade-off. DeepLearning.AI reports that GPT-6.1 Sol scored 52 on the Artificial Analysis Intelligence Index, against 48 for GPT-6 Sol, but generates tokens more slowly (about 58 vs 88 tokens per second). It also drops GPT-6 Sol’s option to turn reasoning off (The Batch).

Related

• ChatGPT plans explained
• ChatGPT vs Claude
• Claude Code vs Codex

Prices checked on October 23, 2026.

Sources

• Official OpenAI: Introducing GPT-6.1 Sol (Sep 29, 2026)
• Official OpenAI: Introducing GPT-6 Sol and Luna (Sep 22, 2026)
• Official OpenAI API pricing (checked Oct 23, 2026)
• Official OpenAI Help: GPT-6 and other models in ChatGPT (checked Oct 23, 2026)
• Reported DeepLearning.AI, The Batch: "Sol Nearly Eclipses Astra"
• Reported TechCrunch, Sep 29, 2026