Rúv News and Earth Science at University of Iceland is reporting that the eruption in Fagradalsfjall at Litli-Hrútur might end in one or two weeks time. This is based on how much the lava flow from the crater is currently decreasing. This would also be mostly in line with the eruption in Meradalir valley in 2021, that lasted for two weeks. This eruption has been slightly longer than that eruption, since it has been slightly larger in volume of magma erupting.
Icelandic reporting on this
Eru goslok handan við hornið? (Rúv.is, Icelandic)
Facebook post reporting on the details of the eruption for 29. July 2023 (Facebook, Icelandic, Possible English)
I would speculate that it will last longer than that by a couple weeks. Mostly because of the gas measurements. They do not seem to indicate that magma supply at depth has slowed, and the current eruptive fissure is on flatter, less thick crust. It is even possible that the eruption continues to issue flows even when the cone itself no longer displays activity, due to the now-covered other fissure vents which are not exposed to the air. It will likely continue until late August, in my opinion. Just an educated guess. The Fagradals and Meradlair eruptions occurred within a mountainous terrain, with more weight on the crust. The current eruption occurred within a relatively fault and unimpeded area, therefore it should have a bit less resistance to close the fissure.
The amount of gas emission now is intense. My current theory is that there is an ‘air pocket’ within the magma chamber which is allowing an expansion and expulsion of the magmatic gases at depth, which are suppressing some of the magma input. It is likely that this is going to continue for a while, allow the eruption to end or subside, but then re-pressurize and erupt in the same place, or a new one. That amount of gas is not normal.
The eruption seems to be over. Based on the harmonic tremor activity, during the night it dropped to almost nothing.