(Bloomberg) -- More than half of workers in major US cities went to the office last week, the first time that return-to-office rates crossed 50% of their pre-pandemic levels.

An index of building occupancies in 10 major metro areas increased 0.9 percentage points to 50.4% in the week ended Jan. 25, according to security firm Kastle Systems. All of the cities tracked by the company — including San Francisco, Chicago and Austin, Texas — reached return-to-office levels of 40% or above, which was also a post-pandemic first. 

Most of the cities tracked saw their occupancy hold steady or rise, including New York, where it increased to 47.5% for the week, and San Francisco, which rose more than two percentage points to 45.9%. Austin had the highest level, at almost 68%, while the San Jose, California, area that includes much of Silicon Valley was the lowest, at 41%. 

The data are based on average weekly access-card activity at buildings with Kastle security systems, compared with a pre-pandemic baseline. 

Read more about Kastle Systems and its back-to-work measures 

Crossing the 50% occupancy threshold is a milestone sure to be cheered by business leaders on Wall Street and elsewhere who have pushed for more in-office attendance. But it comes much later than most return-to-office advocates had expected, due to health concerns surrounding multiple Covid-19 variants, remote-first arrangements by some organizations, and most of all, workers’ reluctance to give up the flexibility they’ve come to enjoy and expect from working from home. 

Many organizations that employ desk workers currently use some type of hybrid arrangement, with workers splitting their time at home and on site. 

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