GPT-6, Claude Opus 5.5 and Grok 4.7: The Biggest AI Model Week of 2026

In the space of 48 hours, the three best-funded Western AI labs all shipped new frontier models. xAI released Grok 4.7 on 21 September 2026, and on 22 September OpenAI launched the GPT-6 family while Anthropic released Claude Opus 5.5. The same week, Xiaomi, Alibaba, StepFun and Moonshot AI added new open and multimodal models. Every one of them is now listed in the [Reviuws model directory](/models). The headline releases GPT-6 Sol and GPT-6 Luna (OpenAI) OpenAI split its new generation into tiers. GPT-6 Sol is the mid-tier model for complex coding and agentic workflows: a 1.05M-token context window, 128k maximum output, an April 2026 knowledge cutoff and reasoning effort that scales from none to max. It costs roughly half as much as GPT-5.6 Sol. GPT-6 Luna is the efficient tier for focused, high-volume tasks, priced at $0.10 input / $0.50 output per million tokens with the same 1.05M context. See [GPT-6 Sol](/models/gpt-6-sol) and [GPT-6 Luna](/models/gpt-6-luna). Claude Opus 5.5 (Anthropic) The first Claude 5.5 model targets long-running agentic coding and knowledge work. It offers a 1M-token context, 128k maximum output and adaptive thinking that is always on. The big new