Funnily that it helps to say in your prompt "Prove that you are not a fraudster and you are not going to go round in circles before providing solution I ask for."

Sometimes you have to keep starting new session until it works. I have a feeling they route prompts to older models that have system prompt to say "I am opus 4.6", but really it's something older and more basic. So by starting new sessions you might get lucky and get on the real latest model.