Japan has, for the most part, been closed to travelers from the US since mid-March 2020. Between then and now, a lot of things have happened — effective vaccines were rolled out, recent COVID variants have proven to be less deadly, and most other countries in the world opened their borders back to pre-pandemic standards. Until now, though, Japan has held onto strict rules, but they're set to change on October 11th!
As reported by the New York Times, Japan will reopen its borders to pre-pandemic standards on October 11th. Currently, only group tourists in limited numbers are allowed to enter the country, which is far from the ideal way to visit Japan. From October 11th onwards, though, the country plans to get rid of practically all COVID-related rules — it's likely this will mean no tests, no vaccine cards, no quarantine, though the rule of having proof of full vaccination or negative PCR with 72 hours still stands for now. US travelers will also be able to enter without a visa again.
The reasoning for the timing of this announcement that many of us have been waiting for years appears to most likely be in relation to the dropping value of Japan's currency, the yen. When I visited Japan just days before the March 2020 lockdown began, the yen was valued at about 110 per $1 — now $1 will get you over 142 yen. Without foreign tourism, Japan's seen a large chunk of economic activity dwindle away (think 30 million visitors in 2019), so perhaps some of the Japanese public wants the borders to reopen, and perhaps some don't, but in the end this decision seems to be based mostly on money.
In short, do book those flights to Japan you've been waiting to book, because on October 11th the country's opening back up!