How was Biblical Greek pronounced?

What they all said. In the modern-day context it doesn’t matter all that much; in terms of historical reconstruction, you’re trying to pin down jelly, since the pronunciation was in flux during the period, though it seems to have been closer to Modern than Attic (though far from identical).

The reconstructions in Greek: A History of the Language and its Speakers, 2nd Edition, I think, allowed that there were different pronunciations depending on social stratum.

One thing a friend pointed out to me (hi Fiona, following us via Facebook): Anglo Christians  pronouncing Koine seem to forget it’s a human language, and put lots of awkward stops between syllables (exaggerated hiatus). Like ParOuSi. A and Agatho. Poi. E. O. I guess that works for them; but Koine was not spoken by robots, just like Homeric Greek wasn’t spoken by yodelling Martians.

See also:

How do you cheer or say “Hooray!” in your language?

Greek.

Ζήτω! Zito!

Now, have I ever written a Quora post on how you say something in Greek, without a detailed disquisition on etymology and alternate expressions?

I won’t this time either.

Zito! is a third person imperative of zo, “to live”: so “may he live!” The third person imperative would certainly have died out by 1000 AD. And “may he live!” looks suspiciously like German Es lebe!

Yes. Like any number of other Modern Greek formulaic expressions, Zito! is a German expression, translated into Ancient Greek. Just like εντάξει endaxi = “OK” is the Ancient Greek translation of In Ordnung.

The Byzantine equivalent, which doesn’t have as much to do with German, is Εἰς πολλὰ ἔτη Is polla eti, “For many years!” That expression survived into modern Greek dialect—and Bulgarian—as Σπολλάτη! Spolati!