The article does not say at any point which model was used. This is the most basic important information when talking about the capabilities of a model, and probably belongs in the title.
It does (unless the previous comment was edited? Currently it says Opus 4.1): https://www.anthropic.com/news/claude-opus-4-1. You can see it in the 'more models' list on the main Claude website, or in Claude Console.