Blocks and Epochs

Aztec uses a decentralized block production system with two key roles: sequencers who produce blocks and provers who generate validity proofs.

Block Production Overview

Block production on Aztec involves several steps:

1. Selection - A sequencer is randomly chosen
2. Block proposal - The sequencer creates and proposes a block
3. Attestation - Committee members validate and sign
4. Proving - Provers generate validity proofs
5. Settlement - Proofs are verified on Ethereum

Sequencers

Sequencers are responsible for ordering transactions and producing blocks. They:

• Collect transactions from the network
• Order them into blocks
• Propose blocks to the committee
• Earn rewards for successful blocks

How Sequencers Are Selected

Each time slot, a sequencer is randomly selected to propose a block. The selection uses randomness from Ethereum (RANDAO), making it unpredictable but verifiable.

This ensures:

• Fairness - All staked sequencers have a chance to propose
• Unpredictability - Nobody knows who will propose until the slot arrives
• Decentralization - No single party controls block production

Provers

Provers generate the cryptographic proofs that make Aztec a valid rollup. They:

• Watch for completed epochs
• Generate validity proofs for all blocks in the epoch
• Submit proofs to Ethereum
• Earn rewards for successful proving

Why Proving Matters

The proofs guarantee that all transactions in a block were valid. Without a proof, Ethereum has no way to verify that Aztec's state transitions are correct.

Epochs

Aztec organizes time into epochs, which are groups of consecutive slots. Epochs serve as the unit for proving:

• Multiple blocks are produced during an epoch
• After the epoch ends, provers generate a single proof covering all blocks
• This aggregated proof is submitted to Ethereum

Why Use Epochs?

Generating a proof for every block would be expensive and slow. By batching blocks into epochs:

• Efficiency - One proof covers many blocks
• Cost savings - Fewer proofs mean lower L1 costs
• Parallelization - Different provers can work on different parts

The Attestation Committee

Not all sequencers propose blocks, but many participate in attestation. Committee members:

1. Receive proposed blocks
2. Verify the transactions
3. Sign attestations if valid
4. Return attestations to the proposer

A block needs attestations from at least 2/3 + 1 of the committee to be considered valid. This provides Byzantine fault tolerance - the network can handle some malicious or offline validators.

Timeline of a Block

Here's what happens during a typical slot:

Phase	What Happens
Selection	Randomness determines the proposer
Collection	Proposer gathers pending transactions
Ordering	Proposer arranges transactions into a block
Proposal	Block is sent to committee members
Validation	Committee members verify the block
Attestation	Committee members sign if valid
Finalization	Proposer collects attestations

Rewards

Both sequencers and provers earn rewards:

• Sequencers receive 70% of checkpoint rewards plus transaction fees
• Provers receive 30% of checkpoint rewards

See Economics for details on how rewards work.

What Happens If Things Go Wrong

The system has safeguards for various failure scenarios:

• Proposer offline - The slot is skipped; next slot's proposer takes over
• Insufficient attestations - Block isn't finalized; transactions return to mempool
• Proof not submitted - Unproven blocks are pruned and must be re-proposed

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For operators

Want to run a sequencer or prover? See the Operator Guides.