Designing a GUI that integrates seamlessly with the real world in Augmented Reality (AR) requires careful consideration of the following factors:

1. Contextual awareness: Understand the user's environment and situation to provide relevant information and interactions.

2. Minimalism: Use simple, intuitive designs that don't clutter the real-world view.

3. Spatial awareness: Consider the physical space and user's movements when placing virtual objects and interfaces.

4. Lighting and shading: Match the virtual objects' lighting and shading to the real-world environment for a cohesive look.

5. User feedback: Provide clear, subtle feedback for user interactions to avoid distracting from the real world.

6. Consistency: Establish consistent design patterns and behaviors throughout the AR experience.

7. Real-world anchors: Use recognizable real-world objects or features as anchors for virtual information and interfaces.

8. User control: Offer intuitive controls that allow users to manipulate virtual objects and interfaces in 3D space.

9. Feedback and guidance: Provide helpful hints and guidance to aid users in interacting with virtual objects and interfaces.

10. Testing and iteration: Continuously test and refine the GUI to ensure a seamless and intuitive AR experience.

By considering these factors, you can create a GUI that harmoniously blends the digital and physical worlds, enhancing the overall AR experience.