Do I have to pay commander tax when casting my commander using Geode Golem's ability?

Question

Hey guys I have a question regarding Geode Golem. Its text says "Whenever Geode Golem deals combat damage to a player, you may cast your commander from the command zone without paying its mana cost. (You still pay any additional costs.)". Does this means that when I deal combat damage with this creature to an opponent and my commander has commander tax, I have to pay the commander tax also?

Answer 1

Yes.
One of the rulings for this card on The Gatherer:

If you cast a card “without paying its mana cost,” you can’t choose to cast it for any alternative costs, such as bestow costs. You can, however, pay additional costs. If the card has any mandatory additional costs, such as the commander tax, those must be paid to cast the card.

Answer 2

Yes, you have to pay the tax whenever you cast your commander from the command zone, whether through Geode Golem or otherwise.

As Geode Golem says, you still have to pay any additional costs. The "commander tax" is an additional cost:

903.8. A player may cast a commander they own from the command zone. A commander cast from the command zone costs an additional {2} for each previous time the player casting it has cast it from the command zone that game. This additional cost is informally known as the “commander tax.”

The total cost to cast a spell is determined so:

601.2f The player determines the total cost of the spell. Usually this is just the mana cost. Some spells have additional or alternative costs. [..] The total cost is the mana cost or alternative cost (as determined in rule 601.2b), plus all additional costs and cost increases, and minus all cost reductions.

Geode Golem merely removes the mana cost of your commander. Additional costs are not affected.

202.1. A card’s mana cost is indicated by mana symbols near the top of the card.