The company said it would likely open most of its U.S. offices at half capacity in September, and then fully in October. Once that occurs, employees who haven’t received approval to stay remote will be expected to come into the office, at minimum, 50% of the time, according to an internal announcement.

In a separate memo to employees, Chief Executive

Mark Zuckerberg

said he personally planned to spend as much as half of the next year working remotely. “I’ve found that working remotely has given me more space for long-term thinking and helped me spend more time with my family, which has made me happier and more productive at work,” he wrote Wednesday.

Facebook’s workplace update comes as Silicon Valley’s biggest companies are firming up office reopening plans, many of which include a combination of remote and in-office work.

Across industries, many companies are offering staff greater flexibility than pre-pandemic as they adopt plans to go back to the office. That is particularly the case in Silicon Valley, where many tech firms saw employees relocate from the Bay Area to less-expensive locales during the pandemic.

Alphabet Inc.’s

Google has said it will move to a hybrid schedule, where most employees work from the office three days a week, while some will be allowed to work from home permanently or shift to an office in a different location.

Apple Inc.

recently said it wants most office workers to show up Mondays, Tuesdays and Thursdays, with the option to work remotely on Wednesdays and Fridays.

Some other companies aren’t pushing employees to go back to the office at all.

Spotify Technology SA

in February adopted a “Work from Anywhere” model letting employees choose whether they want to return to an office, work from home or some combination. And business-software provider

Salesforce.com Inc.

told employees that they have the option to work from home at least through the end of the year, even as it reopens offices. “The 9-to-5 workday is dead,”

Brent Hyder,

Salesforce’s chief people officer, said in a blog post earlier this year.

Unlike Apple, Facebook chose not to designate specific days it expects employees in offices because the way teams work can vary greatly across the company. Instead, it will let individual teams determine when they come in, said

Brynn Harrington,

the company’s vice president of people growth. “If you think about setting days, it’s very hard to do that at a company level and have it connect to the work itself,” she said. “Each team needs something different.”

Mr. Zuckerberg has previously said he expects as much as half of Facebook’s staff to work from home within 10 years.

In his memo Wednesday, Mr. Zuckerberg said the company would need to undergo an adjustment to embrace both in-office and remote work. “Getting this right will take years,” he said.

The company plans to regularly survey employees, asking them to gauge the strength of their personal relationships inside the company and whether they are able to collaborate effectively, for instance. Mr. Zuckerberg also said that Facebook is creating an internal advisory committee to represent the needs of remote employees.

Even as Facebook embraces more distributed work, the company wants offices to remain places for relationship building and collaboration, Ms. Harrington said.

Employees must receive permission from their manager and ultimately approval from a company vice president to work remotely, she said. Some roles, such as in the company’s data centers or hardware labs, can’t be performed virtually. Other individual circumstances, or the needs of a specific team, may preclude remote work.

Though she declined to say how many employees had chosen to stay remote so far, Ms. Harrington said Facebook had approved about 90% of the remote-work requests it had received. Many who have asked for such arrangements have done so because they are relocating to new cities, away from offices, she said.

Facebook previously told employees that locations affect compensation, and that it could reduce salaries for those who move to lower-cost areas.

The company is also leaving open the possibility that its workplace plans will further shift next year. Its guidance on how it expects non-remote employees to use its offices extends through June 2022. “The rationale there is that there continue to be a lot of unknowns,” Ms. Harrington said. “We know we don’t have all the answers yet.”

Write to Chip Cutter at chip.cutter@wsj.com