Rashawn Slater is out indefinitely, with a torn patellar tendon, not too long after he had signed a nearly $30 million / year contract.
Even prior to this, though, Alt had been seen taking reps at LT (started the last game during last season at LT), and he's a natural fit for the position. Seeing how they moved him over right away makes me believe that he's going to be seizing that spot.
I doubt they elevate one of the others to LT, since it's more forgiving letting them cut their teeth at RT. Trey Pipkins was seen at RT after Slater went down.
Link: https://www.chargers.com/news/rashawn-slater-injury-2025-season
….and ND. Cross trains their OL at least in practices.