---
title: SessionPropertyKey
framework: foundationmodels
role: symbol
role_heading: Protocol
path: foundationmodels/sessionpropertykey
---

# SessionPropertyKey

A protocol for defining a custom session property key.

## Declaration

```swift
protocol SessionPropertyKey : SendableMetatype
```

## Topics

### Inspecting a property key

- [defaultValue](foundationmodels/sessionpropertykey/defaultvalue.md)
- [Value](foundationmodels/sessionpropertykey/value.md)

## Relationships

### Inherits From

- [SendableMetatype](swift/sendablemetatype.md)

## See Also

### Custom session properties

- [LanguageModelSession.SessionProperty](foundationmodels/languagemodelsession/sessionproperty.md)
- [SessionPropertyValues](foundationmodels/sessionpropertyvalues.md)
- [SessionPropertyEntry()](foundationmodels/sessionpropertyentry().md)