Something interesting came through on the Sankei Shimbun yesterday, to the effect that Japan was joining AUKUS:
産経ニュース @Sankei_news＜独自＞ＡＵＫＵＳ参加、米英豪が日本に打診 極超音速兵器など技術力期待 https://t.co/TebsV3rm4c 日本政府内ではＡＵＫＵＳ入りに積極的な意見がある一方、米英豪３カ国とは２国間の協力枠組みがあるため、参加の効果を慎重に見極める考えもある
About thirteen hours later came the official denial:
None of this is particularly conclusive. If Japan has been invited to join AUKUS, the announcement almost certainly wouldn’t be coming via a scoop in a mid-circulation regional paper whose readership is exceeded by that of Tokyo Sport. That also doesn’t mean Sankei got it wrong. Japan in AUKUS makes sense on multiple levels — which is why so many people on Twitter immediately accepted the news as fact — and the question of its participation seems more like one of when than whether.