Claude Opus 5.5, GPT-6 Sol, GPT-6 Luna, and a new price war (simonwillison.net)

Anthropic has launched Claude Opus 5.5, while OpenAI introduced GPT-6 Sol and GPT-6 Luna, both significantly cheaper than their predecessors. GPT-6 models now offer a 50% reduction in pricing compared to GPT-5.6, positioning GPT-6 Luna at $0.10 per million input tokens, making it one of the most cost-effective options on the market. This price restructuring is notable as it enhances competition among AI model providers, potentially influencing the choices of developers and businesses relying on these models for application development. Claude Opus 5.5 aims to enhance communication and efficiency, addressing past user concerns. It also offers a 20% price cut on input and output tokens, alongside a drastic 60% reduction in cached token costs, benefiting longer, context-heavy interactions. However, initial tests reveal that its "max" output mode may encounter processing limitations, as demonstrated by its failure to generate a response while reasoning through a complex request. This highlights both the strides made in model design and the ongoing challenges in ensuring practical efficiency, as developers weigh new features against performance reliability.