So Amazon is bigger than Walmart. When will Alibaba overtake Walmart? That will be the day, since there’ll be no help from cloud services The surge added another $40 billion or so to Amazon’s market cap. That will almost assuredly propel it to be more valuable than Walmart for the first time when the stock market opens Friday, making this a deeply symbolic moment for e-commerce and the Internet. It is also a nice present for Amazon, which celebrated its 20th birthday last week.