Day 1, Office building in Denny Regrade, Seattle, US.

Day 1 is a 37-story, 521-foot (159 m) office tower at Lenora Street and 7th Avenue in Seattle's Denny Triangle, part of Amazon's three-tower headquarters. Its dark glass grid facade carries a large "Hello World" sign on the east side, and three intersecting glass-and-steel spheres, 80 to 90 feet tall, face Lenora Street.

Day 1 opened on November 7, 2016, after excavation on the 37-story tower began in 2014 under Sellen Construction. The campus, designed by Seattle firm NBBJ with landscape architects Site Workshop, was approved by the Seattle Department of Planning and Development in late 2012. The project was the most expensive in the city completed in 2016.

The name "Day 1" comes from an Amazon motto about treating every day as the company's first; it previously belonged to two buildings on the South Lake Union campus, both since renamed. The east facade carries a large "Hello World" sign, and the block held the prototype Amazon Go store, open to the public from January 22, 2018 until it closed on February 1, 2026.

Day 1 occupies the block at Lenora Street and 7th Avenue, with the three glass-and-steel spheres facing Lenora Street across a lawn and dog park. The building opened on November 7, 2016; the spheres followed on January 31, 2018. The east facade carries a large "Hello World" sign that can be read from the street.

The east facade carries a large sign reading "Hello World", a nod to the building's role in Amazon's campus. Inside, the block held the prototype Amazon Go store, which opened to a private beta in December 2016 and to the public on January 22, 2018, before closing on February 1, 2026.