tl;dr: At level 45 the experience bar changes its color and fills up for Elite Ranks instead. Each rank lets you pick one out of six random upgrades for that battleframe. Most are small stat bonuses, some are perks of other frames, caches, currency or even a whole battleframe. Every tenth rank offers rare upgrades only.

What Are They?

Elite Ranks are what the game does with the experience you earn after hitting the level cap. They belong to the battleframe, just like the levels, so the upgrades you pick on your Firecat do nothing for your Bastion. There's no cap on the number of ranks. The achievements go up to rank 1'000, with a back banner at rank 50 and titles at ranks 100, 300 and 750.

In update 1.6 every rank cost the same 3'350'000 XP. Update 1.7 replaced that with a curve and reset everyone's points, so they could be spent again.

Experience per Rank

The server doesn't tell the client what a rank costs, the client calculates it on its own from three variables: a base value, a linear part and a quadratic part. With the values the 1962 client ships with, rank n costs

250'000 + 50'000 × (n - 1) + 200 × (n - 1)²

Spending a Rank

Open the character window (default key: P), select your character model and click on Progression. For every unspent point you get six cards and pick one of them.

• A regular rank draws its cards from the common pool, with a chance for one of them to be replaced by a rare one.
• Every tenth rank draws all of its cards from the rare pool.
• Battleframes only show up on the cards from rank 10 on.
• If you don't like any of the six, you can reroll them for 5 Red Beans.
• A respec refunds all stat upgrades of the frame for 100 Red Beans. One-time rewards like Crystite or caches and permanent unlocks like perks and battleframes aren't refunded, since you keep them anyways.
• With 10 or more unspent points the interface skips its animations, which your mouse hand will thank you for.

The upgrades are only shown in the Progression screen, they don't show up in the tooltips of your weapons and abilities. Additionally, they aren't active in PvP, where every frame runs with regulation gear.

Common Upgrades

The percentage upgrades have diminishing returns: the first two picks give 0.5%, then it goes down step by step to 0.1% per pick. Once a stat has reached its maximum, it no longer shows up on the cards.

The ratings are the same ratings modules and tinkering add to, so they stack with those.

Rare Upgrades

Perk Bandwidth is the one to look out for early on. Every pick is one more perk point, and with 49 picks on top of the 36 points from leveling you can afford quite a few more perks.

One-time Rewards and Unlocks

Besides the stats, the cards can also hold things you get once:

• Common: 10 Key Fragments, 15'000 Crystite, 500 Credits, Bronze Tinker's Tools: 8%, Rare Ability Cache, Rare Armor Cache, Rare Module Cache, Rare Weapon Cache
• Rare: 1'250 Credits, 25 Key Fragments, 75'000 Crystite, Epic Ability Cache, Epic Armor Cache, Epic Module Cache, Epic Weapon Cache, Gold Tinker's Tools: 3%, Legendary Fragment Cache, Security Key, Silver Tinker's Tools: 4%
• Perks of other battleframes: They unlock in the order the other frame would get them, e.g. you'll be offered Quick-Flexing Servos before Plasma Enthusiast. An unlocked perk can be used right away, if you've got the points for it.
• Battleframes: Any of the fifteen frames you don't own yet.

Going by the weights in the client's database, a battleframe makes up about 1.6% of the common pool and about 9% of the rare pool, and in both pools an Accord frame is more than twice as likely as an advanced one. In other words: don't count on the regular ranks for a new frame, the tenth ranks are where they come from.

What to Pick?

Personally, I'd take unlocks over stats whenever they show up: a battleframe, a perk I actually want, Perk Bandwidth. After that it depends on the frame. Weapon Damage, Ability Damage and Power Rating help everyone, while something like Deployable Health is wasted on a Recon. The common upgrades are small, but they're also the ones you see on nine out of ten ranks, so pick a few stats that fit the frame and stick with them, instead of spreading the points over everything.