How would you say "it is what it is?" I have heard "eso es" and "eso si que es." I assume the first one is an abbreviation of the second. However, is it an acceptable abbreviation, or is it not something people say?
"Es lo que hay" might be the phrase you're looking for. It is often used to express resignation, sometimes ironically.
I have always heard it said as,
Así es. Especially when asking elders advice about things... they'll say
Así es joven.
This is my opinion is the best translation for
That's just the way it is which I know is not the exact phrase you spoke about, but both our phrases have the same meaning.
It is what it is vs
That's just the way it is
"It is what it is" is literally translated to "Es lo que es". Maybe there is a phrase in Spanish with similar meaning which is used in situations where the English phrase "it is what it is" is used, but I don't think it is very common.
I assume the question mark is not part of the phrase you want to translate: "It is what it is." /lit. Es lo que es./
Spanish has many variations, according to the place where you are speaking it.
In Argentina: Both "Eso es." /lit. That is./ and "Eso sí que es." (with the accent on the "i") /lit. That does be./ could be used to express agreement with something someone just said, like saying "That's it.".
If you tried using it after someone says, for instance, "LAPD gave me a 100USD ticket because the Hollywood sign appeared on the background of my livestream and I didn't have a license from the company that copyrighted it.", then noone would understand. People would expect you to say something more after it, at least an adjective. It would be literally like saying "That is.".
Here in Argentina, a good translation of "It is what it is." is "Así son las cosas." /lit. That's the way things are./.
"Es lo que hay." /lit. It is what there is.; fig. It is what is available./ would work but it's use is better suited for the case where there are many options and you get one that is not amongst the better ones:
-Alice: So... either Trump or Clinton's wife are going to rule the USA for 4 years?
-Bob: Es lo que hay.