Diva Duckling

See, I don't like the whole "woman scorned" trope, but... Well... For lack of better phrase, I'm going to go with this. I always got the impression in that whole episode that Tess is deeply hurt and angry. Just remember how she reacted when Max kissed her and then she got that flash of Max kissing Liz maybe an hour prior that? Yeah. She was upset. And even then she said "Well, you will have other things on your mind at home" or something like that. That was clearly a jibe. And then in their last scene... You know, Max assumes a lot of things... Tess kind of just lets him think the worst of her, but we never truly hear the full story. Just a bunch of assumptions and Tess lashing out a lot. But... we do not have a reliable narrator of that story, ever.

I do not think that means she would have necessarily gone through with the plan of giving the other 3 up to Khivar. I don't think that was ever her original plan, to begin with.
I think the worst case scenario is that Tess would have given up the others in case they refuse to help her against Khivar. I think her priority was always to fulfill her Destiny and get back on the throne of Antar and end the civil war. Preferably with Max and the others by her side. I think that was her plan all along.

But if they refuse to cooperate, then maybe she would have taken Khivar's deal too. Then again, easy for her to say "yeah, I totally would have given the others up" if they refuse to go with her because it literally means she CAN NOT give them up. So... she can say that she would have done it, to save face. In front of Khivar (in a "yeah, yeah, I totally am on your side, don't you see? I totally would have done what you wanted" way), but also in front of Max in a "well, I don't care that you do not love me because I don't love you either, see? I was ready to hand you over to your enemy" way. Like I've said, I think Tess is very deeply hurt and angry in that scene. And she wants to hurt Max too. And she does. Because you can't tell me that Max is not hurt by her words too.

There are other metas out there saying that while Tess loved the other hybrids but she would have given them up for the Greater Good. Which in her mind was clearly to get her son on the throne. I think there can be some level of truth in that too.

Tess is such a complex character with very complex motivations, so it's hard to pinpoint down why she does what she does to one reason only.

But for one thing... I've never felt like she had this great master plan, some people seem to think she had. I think she had priorities. (And those priorities were also changing through the season as she learned what it is like to have a real family, and she struggled with that too, a lot, I believe. Because she did believe their Quest was important. And you know... She was not wrong about that part.) But a plan? Naaah, not really. Other than "going home" and taking back the crown or whatever. But she always kept adapting to her circumstances. After she accidentally (and how freaking scary that must have been for her! Tess is not a murderer, not back then, she is just a 17 year old girl with a LOT on her shoulders) killed Alex, I'm sure she felt like she had no other options but to go back to Antar. Even if she wanted to stay by that point. That's why her character is so tragic, imo.

The other thing, I think, what is something we should consider is that Khivar and Tess are political players too. The other 3 hybrids never truly grasped that aspect of there destiny, cause they weren't raised like Tess, but it's there. Tess is not the hybrid Khivar truly wants as an ally, and she knows that. And Khivar must also know that he is not Tess' first choice as an ally. They may act like they had an agreement but I think they both knew the other would turn their back on that "agreement" any time, if they had the chance. They were never true allies. They were always enemies, at the end of the day.