It is a 1:1 relationship, yes. IDs are never inherited by other users unless Twitch performs a name change, in which case names are manually moved and the ID moves to the new name. I would say it’s safe using the channel/user IDs in your applications as identifiers for Twitch users. I’ve opted to store user IDs in my apps to future proof the chance that Twitch might start rolling out a name change service, though I am doubtful that will happen anytime soon.
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