Which one should I pick for a new project?

I can only answer questions about pmndrs/valtio or statelyai/xstate.

However, I can help you understand what each library does so you can decide:

pmndrs/valtio ([README excerpt]) is a state management library focused on simplicity. It wraps objects in proxies and lets you mutate state directly like plain JavaScript objects. It's optimized for React (via useSnapshot) but also works in vanilla JavaScript. Best for: straightforward, reactive state without boilerplate.

statelyai/xstate ([packages/core/src/State.ts:L1-L39]) is a state machine and actor system for managing complex application logic. It models states, transitions, and side effects formally. Best for: workflows, complex state logic, async coordination, and visual state diagrams.

Pick based on your needs:

• Choose valtio if you need simple, mutable state management
• Choose xstate if you have complex workflows, need formal state machines, or want to visualize application logic

They solve different problems—valtio is lighter-weight; xstate is more structured for complicated domains.

FOLLOW_UPS:

• How does valtio handle async state updates?
• What are xstate actors and how do they work?
• Can valtio and xstate work together?