IOI 2018 took place in Japan in September, 2018. More info is available on the official website.
Just happened IOI 2018 in Japan
The 6th International Olympiad in Informatics was held in Haninge, Sweden in 1994. There were two competition days (Tuesday and Thursday), separated by one day of rest. Each day the competitors had to solve three problems.
Note that the grading model changed at IOI'94 and beyond.
Before IOI 1994, a human evaluator would sit behind the competitor's computer and do the testing manually (enter test data through the keyboard, check the output on the screen). Starting from IOI 1994, an automatic grading process is used, with test input defined in files.