Space Marine 2 Chaos Siege Mode: What Patch 15 Added

Space Marine 2’s Chaos Siege Mode went live with Patch 15 on 1 October 2026, and it is free. For the first time in PvE you play as Heretic Astartes: Cultists and a Helbrute fight on your side, and Tyranids, Cadians and loyalist Space Marines come at you across a new Siege map, Hive, on Avarax. Here is what the Patch 15.0 notes confirm, how it compares with the Siege on Kadaku, and what the notes still leave out.

Saber started a community event for the mode on 20 October 2026. Its event post sets one goal: “survive a total of 15 waves in Chaos Siege Mode before November 03 to unlock 100 Accolades.” The event began the day it was posted.

That sentence is the whole rule set. The post does not say whether the 15 waves are counted per player or for the whole community, which difficulty counts, or at what time on 3 November the event closes. “A total of” reads as waves adding up across matches rather than in one run, but the post does not confirm it, and we have not checked it in play.

Chaos Siege arrived with Patch 15 on 1 October 2026; Saber’s release post calls it part of “Patch 15’s free update” and adds that you play “as Chaos Space Marines in PvE games for the very first time”. Season Pass 3 launched the same day with the Space Wolves Champion Pack and the Exorcists Cosmetic Pack; those are paid cosmetics, the mode is not.

Earlier, the June Community Update had listed the Chaos spin-off of Siege under the free content of Year 3, which the release now matches.

The Patch 15.0 notes describe it this way: players “play as Heretic Astartes in Siege mode. Supported by Cultists and even a Helbrute, players must battle against both Tyranid Hive Fleet forces and the Loyalists.” The new map, Hive, sits “somewhere in the heart of the Hive City” on Avarax, where the Heretic Astartes defend strategically vital locations and attempt their rituals.

Before launch, Saber’s description was one paragraph: “In this mode, you’ll play with Chaos Space Marines on a brand new Siege map located on Avarax. You’ll face Tyranids and Loyalists waves, receive the support of Chaos Cultists and Ritualists, and you’ll be able to deploy a Helbrute to wreak havoc on the battlefield.”

Saber’s September Community Update (24 September 2026) adds two details. You play as Heretic Astartes “warring for the control of Avarax”, culling the Tyranid swarm while Imperial forces and Space Marines try to stop you taking the hive city. And the map has two sectors for now, with a third being worked on. The same post links a short gameplay video of a fight against the Imperial forces.

The June update framed it the same way: you will play “characters that were once limited to PvP only”. Until now Chaos Marines have been playable only in Eternal War, and the closest thing to a playable Helbrute was Patch 10.0’s Helbrute Onslaught, a PvP mode.

Regular Siege is the free wave mode on Kadaku; our Siege Mode guide covers its shop, wave scaling and bosses. Side by side, the differences in Saber’s posts look like this.

Regular Siege facts: enemies and the Helbrute from Saber’s Siege launch announcement, reinforcements from the Patch 8.0 notes.

Hotfix 15.1 (8 October 2026) has a Chaos Siege section of its own:

• Hellbrute: “Summonable Hellbrute melee damage has been decreased by 30%.”
• Portals: players no longer take damage from friendly chaos portals.
• Enemies: Loyalist Marines are “much more effective in killing cultists”, so your Cultist support thins out faster.
• Fixes: weapons now use their Chaos skins in Chaos Siege, and some unprocessed Chaos Space Marine voice lines are fixed.

The notes call it the “Summonable Hellbrute”, so it is summoned rather than available from the start; they still do not say whether you control it once it is down.

Hotfix 15.2 (20 October 2026) adds one Chaos Siege fix: in some cases an enemy Loyalist Marine could spawn behind the closed gates, and that is fixed.

• Which Chaos Marine classes or loadouts you play, and whether your loyalist class levels, perks or weapons carry over.
• How Chaos Siege progression and rewards work, and whether it has its own currency or unlocks.
• Difficulty tiers and squad size.
• Whether you control the Helbrute after summoning it; Hotfix 15.1 calls it the “Summonable Hellbrute”.

The notes do say Saber will take another look at Blessings and Atonements in Siege with Patch 16. Until the mode’s own systems are documented, there is no build or “best class” advice here.

• Crucible Mode: class-specific Penances for Crucible XP and the Lamenters armour set, in 6 tiers. Crucible breakdown.
• One-Handed Thunder Hammer and the Tactical rework: the hammer comes to Tactical, Assault, Bulwark and Techmarine. Tactical can trade its primary for a Power Sword, Power Axe or the new hammer, and a new Signature Perk replaces Signal Jammer so it can carry a Bolt Rifle as a secondary. Tactical rework preview.
• Heroic weapons: three are added: a Power Axe (Frost Axe), the One-Handed Thunder Hammer (Power Maul) and an Auto Bolt Rifle (Iron Hands).
• Wargear Sharing 2.2: a third Wargear slot, capes, tabards and iron halos, plus new Ordeals that unlock tabards and robes.
• Season Pass 3: the Space Wolves Champion Pack (a Bulwark Champion and a One-Handed Thunder Hammer skin) and the Exorcists Cosmetic Pack are paid; Chaos Siege is not.
• Year 3: Patch 15 is the first of five major updates, Patches 15 to 19 (May Community Update). Patch 16 also lands in 2026 with a new PvP mode that uses Weekly Stratagems, and the Apothecary class arrives with Patch 17 in the first quarter of 2027. Year 3 roadmap.

Sources and Confidence