Unnamed sources report that Microsoft has agreed to invest in Uber. Although details are not yet public, the company is expected to invest a significant portion of the upcoming $1 billion funding round that values Uber at around $51 billion. That new funding round — and the valuation — makes Uber one of the most highly valued private companies ever, along with startups such as Xiaomi, a Chinese electronics company valued at around $45 billion and Airbnb, valued at more than $24 billion.

According to The New York Times, an Uber spokeswoman states that the company “filed to authorize this new funding more than two months ago,” but both she and a Microsoft spokesperson declined to comment further. The Wall Street Journal earlier reported on Microsoft’s participation in the funding round.

Uber plans to use part of its war chest to expand into new markets, more specifically, China, India and greater Southeast Asia. An Uber representative said the company had set aside $1 billion to spur growth specifically in India, says NYT, “where the company has faced stiff competition from local ride-hailing services.”

This isn’t the first time that Uber has brought in important partners during funding rounds. NYT reports that Baidu, the Chinese search engine, invested “hundreds of millions” in December and, in March, Times Internet, a Times of India Group media conglomerate, also agreed to “a strategic investment.”

Microsoft’s investment could signal that the Redmond, WA-based company wants to do business with Uber. In 2007, says NYT, it “paid $240 million for a 1.6 percent stake in Facebook, an investment that led to product integrations between the two companies.”

More proof of an emerging partnership possibility comes from Uber’s acquisition of a portion of Microsoft’s mapping technology assets, and offer of employment to more than 100 Microsoft employees. Uber also came out with a mobile app for Windows smartphones, and investing more resources in that platform could help Microsoft’s “struggling mobile app ecosystem.”