OpenAI launched GPT-6 Sol and GPT-6 Luna on September 16, 2026, cutting API (software access interface) prices sharply from their GPT-5.6 predecessors. GPT-6 Sol costs $2 per million input tokens and $10 per million output tokens, compared with $4 and $20 for GPT-5.6 Sol, a 50% reduction for both measures. GPT-6 Luna is priced at $0.10 per million input tokens and $0.50 per million output tokens, down from $0.20 and $1.20. Both new models have lower hallucination rates than their predecessors, while GPT-6 Sol delivers a slight coding improvement. The gains are described as minor rather than transformational. The releases follow GPT-6 Astra, which debuted earlier in September, and mark the third GPT-6 model introduced in one month. GPT-5.6 became publicly available in July 2026, meaning OpenAI is shipping a successor generation less than three months later. A company spending $100,000 per month on GPT-5.6 Sol API calls could theoretically reduce that expense to $50,000 by moving to GPT-6 Sol, while receiving marginally better coding output and fewer hallucination-related incidents.