War for Cybertron: Siege is a subline imprint of the Generations toyline, and the first portion of the War for Cybertron Trilogy.

First revealed in mid-2018 at San Diego Comic-Con, War for Cybertron: Siege, in keeping with the installments of the Prime Wars Trilogy, features a line-wide gimmick: weaponry. Most Deluxe, Voyager, and Leader Class figures each come with at least one or two weapons that can transform, combine, and/or be placed into any C.O.M.B.A.T. System posts, 5 mm posts littered all over their bodies, essentially an updated version of the Powerlinx system and Takara's previous Arms Micron play system. Another line-wide feature is battle-damaged paint jobs on Deluxe-and-up figures to fit with the gritty "war" aspect.

Returning to this toyline are Micromasters, which are bundled in two packs, replacing the Legends Class of the last half-decade, and are now able to combine into large weapons as well as transform into their vehicle form. This size class is also used for Soundwave's minions, who can turn into cassettes or be used as a shield with fold-out pegs.

Replacing the Prime Masters from the last toyline are "Battle Masters", small Targetmaster-type figures that can combine with other weapons and figures. They include additional "Fire Blast" effect pieces that can be placed onto other weapons included with other size classes, as well as hardpoints on the figures themselves to simulate being 'shot' or on the back of vehicles to simulate "rocket boosters" or "speed", depending on the effect part. Each effect part attaches via a 3 mm hole, or in most cases, 5 mm posts too.

Some Deluxe Class figures are classified as "Deluxe Weaponizers," which can be disassembled into multiple weapons to be used in the C.O.M.B.A.T. System. Leader Class figures are very similar to Power of the Primes, in which smaller figures come with additional armor that can be added to vehicle mode or robot mode to increase their size to become the height of a Leader Class figure. This is likely due to robot mode scale playing a much larger role in this series than in the past, with characters sticking reasonably close to their relative heights in the original cartoon.

The boxes of the figures have black-light revealed cybertronian script on them which can be put into the "Found a hidden code?" game on the Transformers website, which unlocks various images, stop-motion videos, and Teletraan-1 Data Files.They, along with the instructions and Siege webpage, also introduce a military insignia system for the Autobots and Decepticons.

Siege was followed by War for Cybertron: Earthrise in 2020, as well as a concurrently-available War for Cybertron Trilogy toylinebased on the Netflix show of the same name.