Severance

Spoilers, obviously.

In the finale, we get the back and forth comedy argument between Seth Milchick (Tramell Tillman) and an animatronic Kier Eagan (voice of Marc Geller, animatronics by Ben Stiller).

I'll quote the exchange below:

Kier: Hail your earthbound steward, your very own flooooooooooor manager!

[audience cheering]

Milchick: Thank you, Kier! And may I say, you're looking very handsome, sir.

Kier: Thank you. I'd say the same of you, if not for my favorite core principle.

Milchick: Probity?

Kier: No ... Vision!

[audience laughter]

Milchick: Well, it's truly special to host a man so illustrious, so sapient, so magnanimous--

Kier: My, you're verbose. Good thing you didn't write the first appendix. It would have burst!

[audience laughter, Milchick visibly discomfited]

Milchick: It's an honor to receive your barbs, Mr. Eagan. The legacy you've left behind is truly and irrefutably larger than life.

Kier: You mean my company?

Milchick: (coldly) No. I mean this wax statue that's five inches taller than you actually were.

[audience chuckles, awkward silence]

Kier: (darkly) Thank you for that feedback, Seth.

Milchick: Thank you, Kier.

This is clearly a prepared routine. It has setups and punchlines and Milchick is visibly reading most of his lines from note cards. However, the performance obviously goes some way off the rails in the back half.

Who wrote this routine? Who performed Kier's lines in-universe? Has Milchick rehearsed this routine or does he only know his own note cards? Is Milchick's height roast part of the script or improvised?

I'll post my thoughts in a separate comment.