Hiro (formerly Blockstack PBC) is a developer tools company building infrastructure for the Stacks blockchain, a Bitcoin Layer 2 that brings smart contracts and decentralized applications to Bitcoin. The company was originally founded in 2013 by Muneeb Ali and Ryan Shea at Princeton University.

Hiro provides developer tools for building on Stacks, including the Hiro Platform (a cloud-based development environment), Clarinet (a local Clarity smart contract development toolkit), and the Stacks.js library for frontend integration. The Clarity smart contract language was designed by Hiro engineers specifically for the Stacks blockchain, emphasizing safety and predictability through its decidable, non-Turing-complete design.

The Stacks blockchain uses the Proof of Transfer (PoX) consensus mechanism, which anchors to Bitcoin's Proof of Work for security. This allows developers to build decentralized applications that settle on Bitcoin while enabling smart contract functionality that Bitcoin's scripting language alone cannot support. The Nakamoto upgrade improved Stacks transaction speeds and strengthened the connection to Bitcoin's finality.

Hiro was one of the first blockchain companies to conduct an SEC-qualified token offering (Regulation A+) in 2019. The company is headquartered in New York City.