Onslaught is bringing co-op gameplay to Battlefield for the first time on console. The new game mode puts you and up to three friends against the enemy on Valparaiso, Atacama Desert, Isla Inocentes and Nelson Bay – redesigned with new lighting, time of day, added vehicles and other effects. Each map has a dedicated gameplay focus, requiring different levels of teamwork in order to complete the objectives against an onslaught of enemy AI. Vehicle warfare comes to the forefront in Atacama Desert while Nelson Bay focuses squarely on infantry assault. Players can compete in squads and check individual progress via the dedicated Onslaught leaderboards.

The question of "What about PC?" is coming up in the comments quite a lot already so this is what the situation is.

No, we haven't signed away rights to console on this.
The problem we have on PC is that all our servers are dedicated with providers. Changing a server from Conquest 32 players to Onslaught 4 players cuts out 28 player slots from the total ammount available. This could have a dramatic affect on the PC online environment if enough servers changed to Onslaught.

We aren't ruling out Onslaught on PC but at this time we are researching how to bring it to PC without affecting players who don't have Onslaught or their own server to run it on.