How many .io domains are registered?

.io is a country extension and publishes no zone file, so this is counted from a list of .io domains that allzonefiles.io compiles instead. That list is refreshed less often than daily, so the line can sit flat for days and then jump when the list is refreshed. The jumps are real changes; the flat stretches only mean the list hasn’t been updated. Compare every extension, or read where the data comes from.