After the resurrection of Guilliman in late [[M41]], he began to see many of the flaws that came from overly-strict adherence to the Codex Astartes. As a result, he has reformed much of the Codex and eliminated much of its restrictions on Space Marines. New additions include the addition of [[Primaris Space Marine]] formations such as [[Intercessor]], [[Aggressor]], [[Inceptor]], and [[Reiver]] Squads, as well as the inclusion of two [[Space Marine Lieutenant|Lieutenants]] below the Company Captain, each commanding a demi-Company. Furthermore, Squads squads in the Codex Astartes are now defined as "[[Battleline Squad|Battlelinebattleline]]" rather than tactical, "[[Close Support Squad|Close Supportclose support]]" rather than assault, or '''"[[Fire Support Squad|Fire Supportfire support]] Squads'''" rather than devastator. These formations exist alongside the not renamed [[Space Marine Veteran|Veteranveteran]] Squads and [[Space Marine Scout|Scoutscout]] Squadssquads.{{Fn|15a}}{{Fn|15b}}

Additionally, the [[10th Company|10th company]] of a [[Chapterchapter]] began to include 10 "[[Vanguard Space Marine|Vanguardvanguard]] " squads alongside the [[Scout Squadscout squad]]s, acting as a permanent infiltration and reconnaissance force that could be attached to other companies.{{Fn|15a}}{{Fn|15b}} As a corollary, the maximum size of a chapter has expanded, as can be seen in the [[Ultramarines#Companies|current roster of Guilliman's first founding chapter]]; as can be seen there, the 10th company contains a full 1,000 marines (formerly it would contain very few, as [[neophyte|non-sergeant scout]]s did not count against the 1,000-man personnel limit in the old Codex Astartes); this means ''even before'' company command structure marines (such as [[space marine command squad|command squad]]s, [[space marine captain|captain]]s, and [[space marine lieutenant|lieutenant]]s), chapter command structure marines, and dedicated vehicle crews (e.g. [[dreadnought]]s), at full strength the Ultramarines have 100 marines assigned to battleline, close support, fire support, and veteran squads (i.e. 1,000 total), ''plus'' 1 marine assigned to each scout squad as its sergeant.