STORY: Wall Street's main indexes ended mixed on Wednesday, with the Dow up about half a percent, the S&P 500 down about half a percent and the Nasdaq lower by one-and-a-half percent.Investors worried about pricey valuations and whether Wall Street's AI rally has reached its peak.Some software companies added to recent losses amid worries that rapidly advancing AI could disrupt industry stalwarts, explains Ross Mayfield, investment strategist at Baird Private Wealth Management."Markets are wobbling a bit lately you know, really as a result of the concentration in big tech. This has been a couple of days, if not a couple of weeks now of headline weakness, but strong breadth. You know, the S&P equal weight, outperforming. You know, nice performance from banks, from industrials, but that's doing, you know, having a really hard time overcoming the weakness in software in particular, which has been really hit hard and is now in a full blown bear market on fears that AI can basically take its job, that these software service companies don't have nearly as strong a moat around their business models as might have been envisioned just a couple of years ago."Alphabet fell more than 2% ahead of its quarterly results after the bell.Shares were volatile in after-hours trading - falling 6% before recouping losses - after the company said it was ramping up AI spending. Investors weighed this against Alphabet's surging revenue and profit, both of which beat expectations for the fourth quarter.:: Advanced Micro DevicesAdvanced Micro Devices tumbled more than 17% after the chipmaker forecast quarterly revenue that disappointed investors and suggested it is having a tough time competing against AI heavyweight Nvidia.Nvidia itself fell almost 3.5%And shares of Palantir slumped almost 12%, reversing sharp gains from the previous day that were driven by the AI data company's strong quarterly sales.:: Eli LillyLimiting losses in the S&P 500, shares of the drugmaker Eli Lilly rallied about 10% after the company forecast 2026 profit above Wall Street expectations.