Check the unit's technology first
To unlock advanced units in Ashes of the Singularity II, start with the technology tied to the unit you want. The official February demo controls open Technologies with T. Once the technology is available, check the unit's recruitment entry for any additional requirements before spending resources on new facilities.
Follow one unit from requirement to recruitment
Choose the unit that serves your immediate plan, such as a more durable frontline option or long-range support. Find its unlock in Technologies and check the prerequisite shown for your faction. When you've met that requirement, return to recruitment and verify that you have a suitable facility or other requirement the game displays.
This sequence helps when the technology is available but the unit still can't be ordered. The first thing to check is whether you've actually unlocked the unit. The second is whether the appropriate recruitment option is available in your match.
Separate the unit unlock from the building chain
In the developer journal on research and building requirements, technology is described as opening units, upgrades, and orbitals. Placed structures are described as opening more advanced buildings. Treat those as separate checks when an option is grayed out. The journal documents the design, and the requirement displayed in your game is the right place to confirm the exact chain.
FAQ
Can one research order unlock every faction's advanced units?
Follow the requirements for the faction you're playing. The developer FAQ describes new and revised rosters, so a unit or prerequisite from one faction is a poor assumption for another.
What should I do if the technology is unlocked but the unit is unavailable?
Open the recruitment entry again and check for the required facility or other unmet condition.
Is T the permanent shortcut?
It's the documented February demo binding. Check your current controls if T doesn't open Technologies.