Yes, Endless Mode is in the full release
The campaign is designed around one hundred days and branching endings. Endless Mode removes the need to treat that campaign horizon as the final test, while Custom Difficulty lets you choose a calmer management experience or a higher-pressure apocalypse.
What changes in a long run
Renewable systems become the real inventory
A large pile eventually runs out. Farming, cooking, traps, power generation, trade and repair capacity determine whether the safehouse can continue. Test each chain separately before expanding all of them.
Organization matters more over time
Use the eighteen storage labels added in V1.0.14331. Separate food, cold storage, tools, materials and crisis reserves so that the survivor does not waste hours searching identical cabinets.
Power needs redundancy
Solar alone is weather-dependent; fuel alone is finite; manual generation spends stamina. Combine a baseline source, stored charge and a crisis source. Keep enough headroom for cold waves and refrigeration.
Difficulty is a design choice
Custom Difficulty is an official feature. Use it to focus a run on farming, base planning or hard crisis management. It is not multiplayer and does not unlock unofficial content.
Current warehouse-manager behavior
The August 17 patch changed Endless Mode so the warehouse manager's cold-storage room, left cabin, garage and right-side areas release unlock tasks gradually during the first few days. Do not assume every area should be open immediately.