Kati is from the Estonian / Finnish / Hungarian Kati — Northern European diminutive of Katerina / Catherine — from the Greek Aikaterine (pure). Kati is one of the Northern European feminine diminutive names — central to traditional Lutheran + Finno-Ugric naming heritage.
Kati does not currently appear in the US Social Security Administration's top 1,000 girls' names, so we don't publish a US rank or birth count for it. That says nothing about the name's standing elsewhere in the world — only that it sits outside the ranked US data we rely on.
In Pythagorean numerology the letters of Kati reduce to 5, The Seeker. This is a traditional interpretive system, not a factual claim about the name.