The Siacoin blockchain is currently 4.3 GB.
Other related questions:
Q: What is current SIA block height?
A: The current SIA block height is 161794.
Q: Who uses Siacoin?
A: Siacoin is used by people who want to store data on the Sia network.
Q: What is Siacoin project?
A: Siacoin is a project that aims to provide a decentralized storage platform. The project is based on the blockchain technology and makes use of smart contracts to allow users to rent out their unused storage space. The project is still in its early stages and is not yet available for use.