The fate of the S&P 500 index is increasingly dependent on whether a few major tech companies can translate artificial intelligence investments into higher profits. Companies like Microsoft and NVIDIA, among seven in total, have driven most of the index's gains. These companies have maintained high stock valuations, with a price-to-earnings ratio of 32, and need to fulfill market expectations for profit prospects. NVIDIA is the primary engine driving profit growth, while other companies have yet to show many benefits from artificial intelligence. The pace of stock price increases has outstripped earnings expectations, instilling confidence in investors about profits but also posing risks.