Hmmm... I'll have to see... cause I'm still gaining EXP at four and still see progress on the bar. Will update if I hit 5. I thought I saw people saying they hit level 10 or something like that... I sure hope so because as of now this fight is next to impossible without cheesing it.
Your XP will go up til you would hit 5, then the bar disappears and it tells you that you've reached max experience. In reality, if you hover over it, you keep gaining experience, but it just wont let you actually level up to 5 =/
Most people who fight them, split their group up, and have ranged up on the bridge. If the gith teleport up there, push them off, they only get 1 teleport each for the ones who do teleport.