With a market capitalization of $168 billion after its pricing at $68/share, the upper end of the range which makes this the largest US IPO in history and would be the largest in the world if the greenshoe is exercised, Alibaba, while not a member of the S&P 500 (at least not immediately), will have a market cap that is larger than the following index members:
In fact, at that market cap (which will surely rise after its break for trading tomorrow), there are only 22 companies in the entire S&P 500 who will be larger than Alibaba, among which the usual mega suspects, AAPL, XOM, GOOG, MSFT, BRK, but also JPM, Facebook, Pfizer, Verizon and Bank of America.
However, assuming BABA rises by 10% tomorrow, it will surpass such tech titans as Intel, and Oracle, now ex Larry Ellison, on its first day of trading.
Sustainble? We shall see.