The official published criteria for Ultima membership is a minimum income of more than S$500,000 a year or S$5M AUM with Citibank. That said, it’s my understanding that Citibank is willing to lower the requirement to S$350,000 or S$2M AUM for selected clients. My contact claims he was still offered the card despite an annual income of “only” S$100,000, so it’s possible there’s some devaluation going on to drive sign ups.
https://milelion.com/2018/04/27/breaking-down-the-citi-ultima-citibanks-500000/