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From what I'm seeing, it doesn't have any APR currently.

I don't believe it ever had interest, only the savings did?

Na.. until a few months ago, SP had a very high "interest" rate.. basically your SP was earning more SP every second. Made the inflation rate way too high with no downside, hence the precipitous drop-off in token value.

Cool to know, had no idea!

checked github, SP is 10% APR but decreasing over time

Hmmmm, very interesting, thanks for pointing that out! I need to peruse the source a bit myself.