For me, it's more tied to narrative milestones than number of sessions. Once the characters have reached (or made definite progress toward) some goal and have a chance to sit down and reflect, that's when it feels most appropriate to level up. It feels a bit awkward when a level is gained in the middle of an expedition into a dungeon - even more so if it's in the middle of an encounter.
As a player, XP is nice.
As a GM, its annoying to track all that and hand it out.
Also its a bit weird with sessions per level. Sometimes your party can mess around for a month and get next to nothing accomplished, next month they could level up twice. Also depends on your session lengths.
In most of my games leveling is done when characters reach specific milestones in the story.
In my sandbox campaign, leveling is strictly XP based. XP does not necessarily mean killing things, it can also means accomplishing goals and solving problems.
Assuming a session is about 6 hours long, which in my groups usually translates to about 4 solid hours of gaming time, I would expect that about every 4-5 sessions a level would occur (this would be true whether I was using the 'milestone' or the xp-method, in either case that is what I would be designing for.)
Obviously this is going to vary from group to group. I could imagine a super focused hard core group accomplishing twice as much (either in terms of story progression or XP) as a more laid back group in the same amount of real world time.
Long enough to get to flex their newfound abilities from the current level, but not so long that the players get bored. I prefer normal track for this reason. We're playing fast track right now though since the AP we're playing specifically recommends it.
Number of sessions is something of an idealized notion. Some sessions (like a dungeon crawl) have a lot of encounters or other experience-granting challenges, while others might only have a few in between long discussions of investigation, decision-making, shopping, or downtime activities.
We're playing fast track right now though since the AP we're playing specifically recommends it.
Which AP suggests fast track for the XP? (I'm assuming it's a 3rd party one?)
As for how many sessions:
I run APs and level up when the AP suggests rather than tracking XP. It usually works out to roughly a level every 3 sessions. Sessions are typically 6-7 hours long.
Which AP suggests fast track for the XP? (I'm assuming it's a 3rd party one?)
Rise of the Runelords: Anniversary Edition and Curse of the Crimson Throne: Anniversary Edition both use fast track by default. I'm running the former.
Like most of the responses, I also look more towards milestones, than a particular number of sessions.
I use both XP and milestones. I award XP for each session, including many awards for things other than combat encounters.
Gaining a level (as soon as the XP amount dictates) isn't automatic. I'll often wait for an appropriate time (milestone) in the adventure. Usually, it ends up being during 'down-time' back at the party's 'base' or back in a town/settlement.
For example, I have a game I run, where the party has more than enough XP to level up. The party is making their way back to a city to re-supply, unload some loot, and research clues they discovered during the mission. During that, is when the level will be added.
Having the characters spend time to visit the temple (cleric), do some research (arcane caster), visit armorer/weapon smith for new equipment and practice with it (martials), seems appropriate as part of gaining a level. (rather than it happening out in the wilderness/dungeon etc.)
Overall, I tend towards slower than average progression. I want players to learn and get used to using what their recent level added to the character (new abilities, spells, skills, feats, etc.) before jumping to the next one. Give them a chance to make it part of their character development and story.
Three to four sessions is my preferred pacing as a player. That usually means 12-16 encounters, and a chance to use my new class features enough to get a proper handle on them without having to reference anything else.
As a GM/DM, I really don't have a preference on how quickly the players level up. I hand out levels at story points, typically, so that the players are the right level for the encounters I have planned for them. The pacing of the adventure usually winds up in their hands, and if they want to push ahead, they get rewarded for it, though they do need to find downtime to rest and prepare their spells/abilities. I tend to award side adventurers (ie, not relevant to the plot) with items, wealth, or other non-experience related loot, though not always.