From the official forums:

Tenno,

As infestation spread across the Solar System, Orokin Ships unable to make the jump to the Void locked down Vault rooms to preserve the valuable artifacts within. A number of these Orokin Vaults have been located in the Orokin Derelicts.

Are you worthy of the hidden treasures within these Vaults? New Corrupted Mods can be discovered here. It will take diligence and cooperation with your fellow Tenno.

To guarantee access to these Orokin Ships, you and your fellow Tenno will need to carry one of each of the four different Corrupted Orokin Vault Keys -- known as Dragon Keys -- into the Derelicts. Blueprints await you in the Market.

Once created, equip your Dragon Key as you would any other mission gear. Because these keys are so powerful, you can only equip one at a time. Be cautious. Each key has debilitating effects on Warframes.

When you find an Orokin Vault, only the CORRESPONDING Key will open the door. Team up with fellow Tenno, each with a different key, to guarantee your entry into the Vaults.

It won't be easy, Tenno, the rewards will not come without cost. Corrupted Mods offer great benefits but also bring negative effects and will need to be applied wisely.

Prepare by gathering your fellow Tenno to work together to ensure your success. More information will be provided today.

• The Lotus

EDIT: This is not an event. The Orokin Vaults will be a permanent addition to Warframe.

Get hype, Tenno!

Any word on when this is launching?

@jakob187:

Right MEOW.

Seriously, go download the update.

And the servers are down =P

Here's the information about the new game mode

Are you ready to enter the Orokin Vaults?

Hidden treasure awaits!

Here's what you'll need to do:

CRAFT A DRAGON KEY

Craft one or all of the Corrupted Vault Keys - also known as Dragon Keys - in the Foundry. Each Dragon Key will require a Blueprint (found in the Market for 500 Credits), any Void Key, and 250 Ferrite.

EQUIP YOUR DRAGON KEY

Equip the Dragon Key in your gear slot. Because these keys are so powerful, only one may be equipped at a time.

Remember, each Key has debilitating effects on Warframes:

- Bleeding Dragon Key: -75% health.

- Decaying Dragon Key: -75% shields

- Extinguished Dragon Key: -75% damage dealt

- Hobbled Dragon Key: -50% speed

These negative effects will be removed from whichever player’s key is used in the Vault.

GATHER FELLOW TENNO

There are four different Vaults and four corresponding Dragon Keys.. When you find the Vault, only the corresponding key will open the door and consume the key.

The mission can be played Solo, but you run the risk of not carrying the correct Dragon Key each time you try to enter. Team up with fellow Tenno, who can each carry one of the four Dragon Keys, to guarantee your access to the Orokin Vaults without delay.

RETREIVE THE REWARD

Once the Vault is open, retrieve the contents and complete the mission before the Ship self destructs.

Successfully complete the mission and your reward will be one of 16 new Corrupted Mods. Each mod offers incredible benefits while also inflicting a negative effect.

Prepare your Keys and enter the Vaults!

OH man it needs a Void Key as a resource that's devious!!!

EDIT:

Dragon key blueprints explicitly now stating they are reusable. (Hotfix)

Seems like all of the negatives can be mitigated by using the right Frame/loadout.

-75% Health - Use a Frame stacked with shields.

-75% Shields - Stack Health/Armor/Use Rhino's Iron Skin

-75% Damage Dealt - Pick a support Frame

-50% Speed - Stack speed mods/play Loki ;) Dual Zorens

The question will be if the rewards are worth it. RNG on 16 different new mods IF you get a vault and IF you have the right key. Will be interesting to see if some keys will be shunned. If so, im gonna make them!

That IS the big question. I've been away from Warframe playing GTA V but I'm about ready to finally give that game a rest and Warframe would be a decent change of pace. My biggest issue always was the inconsistent reward system. I remember defeating the new Golem mega boss with fellow Bombers and receiving a completely worthless reward for it.

They've really been putting a lot of work into this game, haven't they? Seems quite different from that first open beta. Redownloading it now to see what's up.