Palantir Technologies (PLTR -4.63%) has been one of the undisputed winners since the advent of artificial intelligence (AI). The data mining and artificial intelligence (AI) specialist has gained 333% over the past year (as of this writing) and continues to defy detractors. The biggest growth driver has been Palantir's Artificial Intelligence Platform (AIP), which puts the power of AI at its customers' fingertips.

The stock growth has been fueled by seven successive quarters of accelerating revenue growth and 13 consecutive quarters of profitability in accordance with generally accepted accounting principles (GAAP). Add to that Palantir's addition to the S&P 500 and the Nasdaq 100, and it's easy to understand why many were bullish.

However, some investors see the stock flashing red as its stock price has far outpaced its underlying growth, resulting in a sky-high valuation. Furthermore, the Trump administration recently announced plans to cut defense spending by 8% annually. Despite the resulting freefall, Palantir stock is still trading for a blistering 183 times next year's expected earnings, making even bullish investors nervous.

In under two years, Palantir's U.S. commercial segment, which includes AIP, has become the company's most important growth engine. As such, that segment, perhaps more than any other, will have an outsize impact on Palantir's success or failure going forward.

Customers have been flocking to the company's AI Bootcamp sessions. These interactive workshops pair customers with Palantir engineers, allowing them to use AIP to develop mission-critical AI use cases in five days or less.

There's no denying the results. While overall revenue grew just 36% year over year in the fourth quarter, U.S. commercial revenue surged 64%, generating 26% of total revenue.

If growth within the segment were to decelerate, investors would likely take this as a harbinger of things to come. In that case, Palantir stock could face (another) dramatic sell-off -- particularly given its lofty valuation. That's why investors should keep a close eye on the revenue growth rate in Palantir's U.S. commercial segment.