In light of today's high CPI print in the USA and soaring producer prices [1] around the world, in 1990 Brazil reached an annualized interest rate of 790,799% [2]. Unfortunately, HN reroutes the businessinsider link to a different page, so I was forced to post it as a text post.
[1] https://tradingeconomics.com/forecast/producer-prices-change
[2] https://www.businessinsider.com/brazil-historys-highest-interest-rates-2014-2
[2] Archived version: https://web.archive.org/web/20150702062927/https://www.businessinsider.com/brazil-historys-highest-interest-rates-2014-2