@export and underscore members in Godot 4: how to keep internal GDScript state from leaking into scenes

Short answer

Godot 4.x does not provide any language-level access control for GDScript members. The leading-underscore convention is the only signal of intent, and any script that obtains a reference to the node can read or write those members at runtime. Moreover, every variable marked with @export is always serialized into the scene (.tscn) or resource (.tres) file; there is no attribute to keep an exported variable visible in the Inspector while omitting it from serialization.

Confirmed facts

• GDScript has no private, protected, or public keywords.
• If you add @export var speed to a script and save the node, the generated .tscn will contain a line like speed = 10. An underscore-prefixed variable such as _speed never appears in the file.
• From another script, get_node("...")._speed = 5 works fine, demonstrating that the underscore convention does not enforce privacy.

Recommended pattern for Inspector-editable, non-leaking state

1. Store the actual data in a private-convention variable, e.g. _value.
2. Expose a separate @export variable that forwards to the private storage via a setter/getter.
3. Keep all other internal state (timers, caches, intermediate calculations) in underscore-prefixed members or in a helper class.

# MyNode.gd
extends Node

# ---- internal state (private by convention) ----
var _value: float = 0.0          # not exported, not serialized
var _timer: float = 0.0          # internal only

# ---- inspector-editable proxy ----
@export var value: float:
    get: return _value
    set(v):
        _value = v
        # optional: react to the change here
        _on_value_changed()

func _on_value_changed() -> void:
    # react when the inspector changes the value
    pass

func _process(delta: float) -> void:
    _timer += delta
    # use _value and _timer internally; they are never visible in the Inspector

Because only the exported proxy (value) appears in the saved scene, the internal _value and _timer stay out of the file and are not accidentally committed to version control. Other scripts can still access _value if they obtain a reference, but the naming convention makes the intent clear and can be enforced via code review.

When you truly need a non-persisted, inspector-tunable value

There is no built-in way to have an exported variable that is editable in the Inspector and omitted from the scene file. If persistence is unacceptable, avoid @export for that value and instead:

• Use a tool script (@tool) that modifies a private variable at runtime, or
• Expose the value via a custom editor plugin or a temporary debug panel that writes to a private member without saving it.

Accepting the exported variable's presence in the file is the simplest and most reliable approach for most tunable parameters.

Summary

Enforced privacy does not exist in GDScript; rely on underscore naming, code review, and the pattern of exporting a proxy that forwards to a private backing variable. Exported variables always serialize, so keep truly internal state out of @export and accept that any exported value will be persisted.