It’s based on the ASV, which was a revision made to the KJV in the late 1800’s, so textually very similar.

The grammar is updated to be more like the NKJV, but it’s generally more on reverent side than the NKJV is.

The text type of the ASV New Testament was Alexandrian, but they corrected the variants back to Byzantine. However, it’s modern, open source Byzantine critical text, not the Textus Receptus that the KJV used. I think that’s a good thing, but if you’re a Textus Receptus supremacist for some axiomatic reason, you might not like it.

The Old Testament is basically identical to the KJV in every way, including hilarious phrases like “he who urinates against the wall” as a reference to a generic male. Some would argue that’s to a fault, because we know a lot more about Hebrew now, but you can still understand pretty much everything through context clues, just like in the KJV.