Leaked memo from Amazon that warns existing H1B holders to avoid travel back into the USA after the September 21st deadline - their lawyers evaluated the new executive order as not just affecting new applications https://www.businessinsider.com/read-memos-sent-big-tech-trump-h-1b-changes-2025-9
The official White House "rapid response" account on Twitter has now denied that this affects current visa holders https://twitter.com/rapidresponse47/status/1969476188008575149
The official USCIS Twitter account has confirmed that the new policy will NOT affect existing visa holders - hopefully they are a trustworthy source here since they are the agency that has to implement the new policy! https://twitter.com/uscis/status/1969515779251953876
USCIS (@USCIS) on X

President Trump’s new H-1B visa requirement applies only to NEW, prospective petitions that have not yet been filed. Petitions submitted prior to September 21, 2025 are not affected. https://t.co/YZmqtpE8N3

X (formerly Twitter)
@simon
Since Trump could decide that's not right, in principle anyone who care should assume that it doesn't matter whether the people in the institution are trustworthy.