is it required to salute while in Army PT uniform?

It's an official Army uniform, so yes. Especially if you recognize the other person in APFUs as an Officer.

Wait, no disrespect, but aren't you a SNCO?

I saw a situation where a CPT in BDUs called out a Soldier in PTs for not salutng him. Turned out that the PT uniform was a MAJ.

However, if you know that someone is an officer, regardless of what uniform either is wearing, and you are not an officer, then yes, you should salute

Army is weird.....when I was in the Marines, we only saluted when wearing a cover (pc, etc), to include for colors and such. After about a week in the Army, I was asked if I was unpatriotic or something because I didn't salute the flag in pts during colors...

And this is why we now have everyone with more than one stripe putting rank insignia on PT Belts.
Which, by the way is unauthorized:

"10–10. Insignia
The only insignia authorized for wear on the APFU is the physical fitness badge. When the physical fitness badge is worn, it is sewn on the wearer’s upper left front side of the APFU t-shirt above the word “Army.” On the APFU running jacket, the insignia is sewn centered and 1/2 inch above the Army logo. See AR 600–8–22 for criteria for wearing the physical fitness badge."
DA PAM 670-1

You didn't learn this in Basic?

You didn’t know? I’m a Marine and knew that

You just said it, in uniform. A uniform is just that. If you know the individual is an officer, salute away

When I was serving there was no such thing but I would guess since it is a prescribed uniform and a salute is prescribed for a salute when in uniform.

I swear some of the questions on here at times make me wonder if they’re just put to be humorous or if the person(s) are serious.
When the question itself asks if you salute while in a PT uniform, with a MASSIVE freaking emphasis on uniform, i’m not even sure how you finish the question quite frankly. It is a authorized uniform, therefore you Conduct yourself just as you would any other time that you were in uniform. You salute in your dress uniform, your battle dress uniform, your PT uniform, and or any other authorized military uniform period. That’s a very simple concept that an E-1 should be able to answer, let alone anyone else that’s served in the military more than a day.
I will say however that in the event you are jogging or pass up a person that you do not know to be an officer you cannot be expected to just know who the hell they are, but for Pete’s sake if you know that they are in your chain of command, whether it be at the company level or all the way to brigade and above then render a salute. How does the old saying go, when in doubt whip it out, and not like some people are thinking and laughing right now LOL.
Personally as an officer, I never stopped someone in the event that we were conducting PT and they did not render a salute because for the most part I would rather you be pushing yourself and completing the physical activity that you were doing I am looking like a crazy person all over the place trying to salute or figure out if you’re supposed to. Other officers not so much, or if they have a PT belt on and you were able to see the name and or rank than that is very self-explanatory.

I believe it depends, I’m not sure if it’s just our policy or if it’s a reg. But from what I understand, yes you salute in PTs, however if you are actively engaged in group pt you do not render a salute.