# 0001: Pin Unreal Engine 5.5 LTS

Status: Accepted

Date: 2026-05-23

## Context

V4 spans tactical FPS, stealth tactics, action RPG, RTS, and 2D arcade cells.
The project needs a stable engine baseline so gameplay code, binary assets,
platform cooks, and third-party middleware do not drift during launch
development.

## Decision

V4 pins the launch branch to Unreal Engine 5.5 LTS. `V4/ue/V4.uproject` uses
`EngineAssociation` `5.5`, and CI jobs are named and configured around UE5.5.

## Consequences

- Engine upgrades during the launch window require a new ADR and migration plan.
- Plugins and middleware must certify against UE5.5 before they can enter the
  launch branch.
- Automation workers must expose UE5.5 editor and commandlet paths through
  `UE_EDITOR` and `UE_ROOT`.