New AI Models: Opus 5.5, GPT-6 Sol & GPT-6 Luna

It was a big day in AI. Three bleeding-edge models landed today—Anthropic's Claude Opus 5.5 and OpenAI's GPT-6 Sol and GPT-6 Luna. All three are now in Sudowrite.

• Claude Opus 5.5 is the first model in Anthropic's new Claude 5.5 family. Anthropic says it performs at the level of Fable 5.1 on most work, while running more than 30% faster than Opus 5. Anthropic says the writing is clearer, follows instructions more closely, and as one early tester told them, "it writes the way I do."

• GPT-6 Sol and GPT-6 Luna round out OpenAI's GPT-6 family below Astra. Sol is super smart and makes about half as many factual whoopsies as its predecessor—making it great for Story Bible adherence and a solid choice for Plugins. Luna is the quick, inexpensive choice: useful for lots of shots on goal, brainstorming… anything where you want to generate a lot and sort it out afterward.

• Each of them uses fewer credits than the model it replaces. In early side-by-side runs on the same passage with the same inputs, GPT-6 Sol came in around 40% cheaper than GPT-5.6 Sol, GPT-6 Luna around 10% cheaper than GPT-5.6 Luna, and Opus 5.5 just barely cheaper than Opus 5. There’s a big gap between these models though, with Sol at roughly a third of Opus 5.5's credit cost, and Luna at about a seventh.

That’s a lot of numbers for a site about words though, and what matters is what you think of their prose. All three are available now in Write, Draft, and Plugins. Give them a spin and let us know what you think.