  The consensus protocol is a critical component of distributed ledgers and
blockchains. Achieving consensus over a decentralized network poses challenges
to transaction finality and performance. Currently, the highest-performing
consensus algorithms are speculative BFT algorithms, which, however, compromise
on the transaction finality guarantees offered by their non-speculative
counterparts.
  In this paper, we introduce Albatross, a Proof-of-Stake (PoS) blockchain
consensus algorithm that aims to combine the best of both worlds. At its heart,
Albatross is a high-performing, speculative BFT algorithm that offers strong
probabilistic finality. We complement this by periodically guaranteeing
finality through the Tendermint protocol. We prove our protocol to be secure
under standard BFT assumptions and analyze its performance both on a
theoretical and practical level. For that, we provide an open-source Rust
implementation of Albatross. Our real-world measurements support that our
protocol has a performance close to the theoretical maximum for single-chain
Proof-of-Stake consensus algorithms.
