Shooting up from the downtown skyline is a gleaming 66-story glass behemoth, a place “where Fortune 500 companies, high-rise residents and premier retailers come together to create a community of their own,” as sleek marketing brochures put it. The tech giant Meta scooped up all 19 floors of office space as construction was underway in early 2022. But when Austin’s tallest building officially opens later this year, all that office space will be empty, the Washington Post reported. Meta has ditched its move-in plans and is now trying to sublease 589,000 square feet of offices, 1,626 parking spots, 17 private balconies and a half-acre of green space. So far: no takers. The skyscraper known as “Sixth and Guadalupe” is a prime example in the city that made a huge bet on the post-pandemic commercial real estate economy. While other cities worry about a glut of office space as workers resist returning to the familiar 9-to-5 grind, Austin’s challenges are Texas-sized. Here, about 6 million square feet of new office space will hit the market in the next few years — equivalent to 105 football fields. Between spaces completed since 2020 and what’s still in the pipeline, the office market will grow nearly 25 percent — the fastest rate on the continent. That includes projects such as the Waterline, which will become the tallest building in all of Texas, at 74 stories, when it opens in 2026, and a mammoth 1.1 million-square-foot complex on the city’s outskirts where a former 3M campus is being redeveloped (into what, exactly, is still unclear). And the vast majority of projects are blazing ahead without companies lined up to move in. Roughly 87 percent of new office space is expected to open vacant, according to data from the commercial real estate firm Cushman & Wakefield.