After well over a decade of lagging behind, Audi is finally about to launch itself into the top-tier of mammoth luxury SUVs to combat the BMW X7 and Mercedes-Benz GLS. We suspect BMW isn't going to wait nearly that long for a response to Audi's challenge.And now, CarBuzz uncovered a recent trademark filing to support that theory. It's not for BMW directly, but rather, for Alpina, which is now officially part of the company but still positioned as a distinct brand. And the trademark suggests something truly big is coming.BMW Snags Trademark For Bigger Alpina ModelCarBuzz/Valnet Earlier this month, BMW filed for the trademark Alpina XB9 in Germany. Alpina is BMW's now fully in-house tuner brand, bought recently after decades of a very close partnership that saw Alpina models built at BMW plants and sold in BMW dealers. It makes vehicles that are more like grand tourers than BMW's own high-performance M cars.Alpina is the brand, and for the last 20 years or so it has used a very predictable name scheme. Under Alpina's naming, an XB9 would be a gasoline-powered (B for benzin) X9. But there isn't a BMW X9, right? Exactly.A larger-than-X7 SUV, called the BMW X9, has been hinted at by brand executives for years. Dealers, especially in the US, are reportedly seeking a larger vehicle to compete with the Cadillac Escalade. It's one segment in which the German brands just haven't been able to compete. And with trends in the US being more favorable to large, thirsty SUVs, now might be the time to pounce.In March, BMW executive Bernd Koerber said that a larger SUV had potential, but that "It's still a question of whether that would be a right thing for us to do." It would still need to drive like a BMW, and that means a much better ride and sharper reflexes compared to Escalade or the Lincoln Navigator.BMW has plenty of room to move upward from the X7. A loaded X7 comes in under $130,000, while the Alpina XB7 with more power, torque, and luxury features, starts at just over $150,000. A top-spec Escalade is actually more expensive than an X7, with an Escalade V topping $170,000. That's a lot of extra cash per transaction for BMW to leave on the table.But the XB9 trademark isn't the only indication BMW is serious about building an X9. Another clue comes from an unexpected legal battle with a Chinese automaker. The B In XB9 Could Stand For 'Big' BMW That other clue actually stems from a trademark that BMW does not own. Last October, China's Xpeng Motors applied for the X9 trademark in Germany. BMW opposed the mark in January, saying that it was likely to be confusing to buyers. BMW could argue that X followed by a single digit is its thing, but the two events combined strongly suggest that there's a new model coming.BMW could build a larger SUV on a modified version of the platform that underpins the current X7. That would help it build this very US-centric model at its plant in South Carolina.It's also possible that something this big could need more space, but BMW also has that covered. The Rolls-Royce Cullinan SUV is built on a frame called the Architecture of Luxury that has a wheelbase almost 8 inches longer than the X7's. That's the perfect length for a theoretical X9, should BMW be able to make the figures work.Cadillac's Escalade has been the undisputed champion of massive luxury SUV sales for nearly 30 years. The target might finally be too big for BMW to ignore.Trademark filings do not guarantee the use of such nomenclature in future vehicles and are often used exclusively as a means of protecting intellectual property. Such a filing cannot be construed as confirmation of a production-bound application.Source: DPMA