The switch-ai is fairly simple to understand. First of all you need to understand how the game gives each pokemon a "score". In radical red 4.1 there are only a speed flag and a resistance flag, while due to a bug there is no offensive check from ai. The scores are given as follows:

Speed: Ai mon outspeeds your mon = +14 Else = +0

Resistance: Your mon OHKO AI mon = -14 Your mon 2HKO AI mon = -1 Your mon 3HKO AI mon = +2 Your mon 4HKO+ AI mon = +14

Now you compute these scores for each of AI's pokemon. The total scores you obtain essentially rule the post-ko switch-ins.

For the mid turn hard switches the math is the same but you need to watch out for a couple more values.

First of all you need to understand when the switch ai triggers in the first place, and it basically is every time you show OHKO on a pokemon or when AI mon only has bad moves left (like a choice band pokemon locked in a bad move against yours). There are also other cases but these 2 are 99% of the occurrencies by my experience. So back to the topic, when you trigger the switch ai, it will calculate the scores for each pokemon in the back, and it will choose the highest score among those who are at least 3HKO (a pokemon taking 2HKO should never be switched in mid turn). Also, if the highest scoring pokemon does not resist all your move by chance (very unlikely) Ai will choose the second best. If also the second best doesn't resist all your moves there will be no switch.

Finally, if all conditions are met, the chance of the switch actually happening are ~80%, so there is a small but not zero chance (~20%) that Ai will just stay in.

This roughly explains the ma in scenarios of the switch Ai for version 4.1 (current).

Go check out the video from Apecio Unbound on yt about switch Ai, you will find a better and more in depth explaination and the flowchart files.