Dominating the Austin skyline at 56 stories, the Austonian officially "tops out" on Thursday.

Hundreds of workers with construction company Balfour Beatty who've been working on the 683-foot high-rise will celebrate with a party Thursday afternoon. A 32-foot structural steel beam signed by the construction team will be hoisted by crane across Congress Avenue to the top of the building at 4:30 p.m. The beam is one of six that will support the building's ornamental glass crown.

Construction on the $250 million, 188-unit luxury condo tower began two years ago. Completion is scheduled for spring 2010.

Benchmark Development, the Austin-based subsidiary of Spain-based Grupo Villar Mir, is the developer of The Austonian. Ziegler Cooper Architects of Houston designed the project.