Glossary OS

Plain meaning

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The sub-second transaction finality goal of the Alpenglow consensus protocol, targeting approximately 150 milliseconds from block production to irreversible confirmation. Fast finalization is achieved by replacing Tower BFT's exponential lockout mechanism (which requires ~31 confirmations over ~12.8 seconds) with Alpenglow's certificate-based approach where a single round of supermajority voting produces an irrevocable finality proof.

Mental model

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Technical context

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Consensus, leader rotation, slots, epochs, and the runtime.

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Fast Finalization (fast-finalization)
Category: Core Protocol
Definition: The sub-second transaction finality goal of the Alpenglow consensus protocol, targeting approximately 150 milliseconds from block production to irreversible confirmation. Fast finalization is achieved by replacing Tower BFT's exponential lockout mechanism (which requires ~31 confirmations over ~12.8 seconds) with Alpenglow's certificate-based approach where a single round of supermajority voting produces an irrevocable finality proof.
Related: Alpenglow, Alpenglow Certificate, Finality

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Concept graph

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Branch

Alpenglow

A next-generation consensus protocol proposed in SIMD-0326 that aims to collapse Solana's legacy systems (Proof of History, Tower BFT, gossip-based vote propagation) into two streamlined mechanisms: Rotor for data propagation and Votor for off-chain voting. Alpenglow targets reducing transaction finality from ~12.8 seconds to under 150 milliseconds, representing the most significant consensus overhaul in Solana's history.

Consensus Mechanism Tower BFT

Open term

Branch

Alpenglow Certificate

A fast finality certificate produced by the Alpenglow consensus protocol when a supermajority of validators (66.7%+ of stake) have attested to a block through Votor's off-chain voting mechanism. Once an Alpenglow certificate is formed, the block is considered final, reducing finality time from Tower BFT's ~12.8 seconds to a target of under 150 milliseconds. Certificates are compact proofs of consensus that can be verified by any node.

Votor Supermajority

Open term

Branch

Finality

The guarantee that a transaction cannot be reversed. Solana offers two levels: optimistic confirmation (~400ms, 66.7%+ stake voted) and full finality (~12-13 seconds, 31+ confirmations rooted). Once a slot is rooted, its transactions are irreversible under the assumption that no more than 1/3 of stake is malicious.

Confirmation Optimistic Confirmation

Open term

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Core Protocol

Alpenglow

A next-generation consensus protocol proposed in SIMD-0326 that aims to collapse Solana's legacy systems (Proof of History, Tower BFT, gossip-based vote propagation) into two streamlined mechanisms: Rotor for data propagation and Votor for off-chain voting. Alpenglow targets reducing transaction finality from ~12.8 seconds to under 150 milliseconds, representing the most significant consensus overhaul in Solana's history.

Open term

Core Protocol

Alpenglow Certificate

A fast finality certificate produced by the Alpenglow consensus protocol when a supermajority of validators (66.7%+ of stake) have attested to a block through Votor's off-chain voting mechanism. Once an Alpenglow certificate is formed, the block is considered final, reducing finality time from Tower BFT's ~12.8 seconds to a target of under 150 milliseconds. Certificates are compact proofs of consensus that can be verified by any node.

Open term

Core Protocol

Finality

The guarantee that a transaction cannot be reversed. Solana offers two levels: optimistic confirmation (~400ms, 66.7%+ stake voted) and full finality (~12-13 seconds, 31+ confirmations rooted). Once a slot is rooted, its transactions are irreversible under the assumption that no more than 1/3 of stake is malicious.

Open term

Core Protocol

Feature Gate

The mechanism for activating protocol changes on Solana's mainnet cluster. Each feature is identified by a unique pubkey and activated when validators representing a supermajority of stake signal support by creating a feature account. Feature gates control runtime behavior changes, new syscalls, parameter adjustments, and program upgrades. This system allows gradual, stake-weighted rollout of protocol changes without hard forks.

Open term

Related terms

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Core Protocolalpenglow

Alpenglow

A next-generation consensus protocol proposed in SIMD-0326 that aims to collapse Solana's legacy systems (Proof of History, Tower BFT, gossip-based vote propagation) into two streamlined mechanisms: Rotor for data propagation and Votor for off-chain voting. Alpenglow targets reducing transaction finality from ~12.8 seconds to under 150 milliseconds, representing the most significant consensus overhaul in Solana's history.

Open term

Core Protocolalpenglow-certificate

Alpenglow Certificate

A fast finality certificate produced by the Alpenglow consensus protocol when a supermajority of validators (66.7%+ of stake) have attested to a block through Votor's off-chain voting mechanism. Once an Alpenglow certificate is formed, the block is considered final, reducing finality time from Tower BFT's ~12.8 seconds to a target of under 150 milliseconds. Certificates are compact proofs of consensus that can be verified by any node.

Open term

Core Protocolfinality

Finality

The guarantee that a transaction cannot be reversed. Solana offers two levels: optimistic confirmation (~400ms, 66.7%+ stake voted) and full finality (~12-13 seconds, 31+ confirmations rooted). Once a slot is rooted, its transactions are irreversible under the assumption that no more than 1/3 of stake is malicious.

Open term

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Core Protocol

Proof of History (PoH)

A clock mechanism that cryptographically proves the passage of time between events. PoH uses a sequential SHA-256 hash chain where each output becomes the next input, creating a verifiable ordering of events without requiring consensus. The leader produces ~400,000 hashes per slot (~400ms), and any validator can verify the sequence in parallel, enabling Solana's high throughput by removing the need for validators to agree on time.

Open term

Core Protocol

Tower BFT

Solana's custom BFT consensus algorithm built on top of Proof of History. Tower BFT uses PoH as a clock to reduce communication overhead in traditional PBFT from O(n²) to O(n). Validators vote on forks with exponentially increasing lockout periods—each consecutive vote doubles the lockout, making rollbacks progressively more expensive. A fork is finalized when it reaches supermajority (66.7%+ of stake).

Open term

Core Protocol

Slot

A time window during which a designated leader validator can produce a block. Each slot lasts approximately 400 milliseconds. Slots are numbered sequentially from genesis and grouped into epochs of 432,000 slots (~2-3 days). Not every slot produces a block—a skipped slot means the leader was offline or too slow.

Open term

Core Protocol

Block

A set of entries produced by a leader during a single slot. A block contains transactions bundled into entries, each with a PoH hash proving ordering. Blocks are broken into shreds for network propagation via Turbine. Maximum block size is limited by compute units (48M CU cap per block) rather than byte size.

Open term