Hard to see from here. Possibly all of the above, or even more.

I agree, all of the above. I would have them back and make sure they reinstall it properly, and maybe read about window installation yourself, so you know that its done right, this time. Thats a lot of water coming in that window.

Flashing would be to the exterior so show a picture from the outside. Caulk is not necessarily the answer as it is not the major line of defense, that would be the head flashing. My gut says the head flashing is missing since it is leaking at the top and the ceiling (?) appears pretty close to window head height, but impossible to tell from the picture. I agree on calling back the installer.

As the others have alluded to, its impossible to diagnose from these pics. Some shots from the exterior would be helpful.

Also as MWM mentioned, while caulking can stop leaks, its not the primary line of defense. Ideally, a properly flashed window or door will be leak-proof with no caulking at all. Depending on how it was installed that is not always the case, however it is best practice.

Pics from outside please. Likely coming from what is above the window here. This can happen when we remove a nailing flange equip window and go back with a retrofit. The reality is that the previous window was already leaking, but the nailing flange was helping conceal that issue.