Anthropic Launches Claude Opus 5.5, OpenAI Counters With GPT-6 Sol and Luna

Anthropic released Claude Opus 5.5 on Tuesday, Sept. 22, 2026, cutting typical workload computing costs 40% below Opus 5 while boosting output speed more than 30%. OpenAI responded within hours by launching GPT-6 Sol and GPT-6 Luna, escalating competition from benchmark performance to price and inference efficiency. Opus 5.5 scored 66.4% on Terminal-Bench 4.0 versus 52.3% for Opus 5, and 1846 Elo on GDPval-AA v2.1. API pricing fell to $4 per million input tokens and $20 per million output tokens, each 20% lower than Opus 5, with cache reads dropping 60% to $0.20. OpenAI priced GPT-6 Sol at $2 per million input tokens and $10 output; GPT-6 Luna at $0.10 input and $0.50 output, with 90% cache discounts. Both models are available via API and ChatGPT. Anthropic said Sonnet 5.5 and Haiku 5.5 will follow in coming weeks. Opus 5.5 is available on AWS, Google Cloud and Microsoft Azure.