Do the extra spells from the XGtE ranger archetypes expend a spell slot when cast?

Question

In XGtE the Ranger Archetypes are awarded additional spells at specific levels.

For example the Monster Slayer archetype receives Protection from Evil and Good at 3rd level. XGtE states The spell counts as a ranger spell for you, but doesn't count against the number of ranger spells you know, so this would mean the a third level Monster Slayer would know Protection from Evil and Good plus three spells.

Does this mean that they still only have three spell slots to use, they have an extra spell slot, or can they cast Protection from Evil and Good without expending a slot?

The way I interpret the rule is that (in the above example) the Monster Slayer knows three spells plus Protection from Evil and Good, but still only has three spell slots to use.

Answer 1

The extra spells via XGtE archetypes do not grant an extra spell slot, but still require expending spell slots to cast

There is no relation between the number of spells you know and the number of spell slots you have.

As a 3rd level ranger, you will have 3 spell slots.
As a 3rd level ranger, you will have 3 known spells.
As a 3rd level ranger with a XGtE archetype, you will know one additional spell as per your class feature (e.g. Monster Slayer Magic).

Knowing a spell, regardless of whether it comes from standard class features (i.e. Spellcasting) or an archetype feature (e.g. Monster Slayer Magic), doesn't change how you cast it (given that they are still considered ranger spells in either case). It simply says (XGtE, p. 43):

[...] you learn an additional spell when you reach certain levels in this class, [...] The spell counts as a ranger spell for you, but it doesn't count against the number of ranger spells you know.

It doesn't say that it grants an extra spell slot, just an extra spell. It says it doesn't count against the number of spells you know (which is simply stated as so not to "use up" what would otherwise be a player's spell choice), but it otherwise counts as a ranger spell, meaning subject to how ranger spells work as per your Spellcasting feature, which means it requires expending spell slots. From Spellcasting (PHB, p. 91):

To cast one of these spells, you must expend a spell slot of the spell's level or higher.