that is all

HLAs are learned when your current class XP exceeds 3,000,000. Multi class is total XP at the same amount.

thanks

Can't remember the level for rogues, but if you are curious about the level range for HLAs - they come around 17-21, depending on the class.

A few other technical points:
* The requirement is >= 3,000,000 XP, not > 3,000,000 XP. Many classes (including Fighter and Mage, for example, but (IIRC) not Thief, actually get a level at exactly 3 million XP, and will gain an HLA at that point.
* Dual-class characters only count the XP gained in the second class. (I believe you can get an HLA for the first class if you get 3 million XP before class changing, but doing so will result in you losing that class's abilities and not getting it back until (maybe) near the end of the game, and you won'g get any more HLAs until that point, so I don't recommend it. I think you *might* retain the use of the HLAs you learned, as long as they don't require spell slots.)
* In the classic edition, Ranger/Clerics have the levels that they get HLAs mixed up, resulting in getting HLAs for Cleric levels earlier than intended, but HLAs for Ranger levels later. This means you start getting HLAs early (I believe before you even get 7th level Cleric spells), but you end up with about the same number as if this bug weren't present. I believe it also menas that, if you are playing the original release and wait to install Throne of Bhaal until you are past that level, you won't end up with as many HLAs. (This last point doesn't apply to the GOG version, as it comes with Throne of Bhaal pre-installed. Also, I would expect the Enhanced Edition to not have this bug in the first place.) It's lower for multi-class characters. In the extreme case, I believe that, in the classic edition, Rangers start getting them at Cleric level 13 (not Ranger level 13, as was presumably intended) and Ranger level 15 (not Cleric level 15). Triple class characters get them at even lower levels (though they can't get and Mage HLAs ever, not even the ones that add bonus 6-8th level spell slots).

Edit: For single-class rogues, it's level 24.

You retain the abilities you get from high levels, even before you are at higher levels with your new class. That means you can start as a fighter, level to some and twenty, and then still have that sweet whirlwind attack as 1st level thief (for example).