From Halopedia, the Halo wiki
The helmet has an Ankara EV-A760 wide-range visor set, closed-breach sensor components that open at the operator's request, and a Twin-case Class-8 support module (KR-03-A) used to improve suitability in space. The helmet also contains heavy duty connectors and data ports for external attachments, though GEN2 specifications did not require it.
Prior to the Human-Covenant War, "jaunt-combat excursions" were not seen as relevant or practically viable; this changed after the war started, leading the UNSC creating the "Strider" term for operators who conduct highly varied missions over a short period of time.
The Strider-class armor system was designed explicitly for Strider activities in which the suit has more endurance than most Mjolnir systems, handily resolving multi-task aggregation, coordinating missions on the fly, and effectually giving the operating Spartans the solvency needed to execute accordingly.
After it was released the suit had become the unofficial base for heavily customized "frankensuits" due to its relative simplicity and extensively documented subassemblies.
Unlock: Unlocked by getting the War Games Map Pass. It is also available in the Halo 4 Game of the Year Edition.
Halo 5: Guardians
Unlock: Rare REQ pack
In Halo 5: Guardians due to the "Body" having a predefined customisation this armor set permanently has the following parts from Halo 4:
Halo 4 skins
Halo 5: Guardians skins
List of appearances