https://gamepress.gg/arknights/data...ent-tag-appearance-and-rarity-rate-statistics
According to the author:
With a sample size of 2442, the alpha value set to 5%, the margin of error is 0.18%, 95% confidence interval for getting a Top Operator Tag is 0.03%-0.38%
Interesting Results Summary
Chances of getting Top Operator is roughly 1 in 500 recruitments.
Chances of getting Senior Operator is roughly the same as Top Operator.
Chances of getting any Tag that alone guarantees a 5 Star or higher Operator is around 1 in 112.
Here are the approximate rates of getting the following rarities:
3★: 73%
4★: 25.7%
5★ or 6★: 1.3%
For more details, you can check out FivePlop's reddit post here.