Solana Alpenglow went live on mainnet on Wednesday, October 21, 2026, replacing TowerBFT, the consensus protocol the network had run since its 2020 launch. Anza, the core engineering team that built the upgrade, said validators retired TowerBFT at slot 459,653,000 at about 14:00 UTC.

In its announcement, Anza says transactions now become irreversible in about 150 milliseconds, down from 12.8 seconds. That figure is Anza’s design target and its own description of the result; the announcement does not cite an independent measurement.

How the switch happened

The Solana Foundation’s Alpenglow upgrade page gives the sequence. The feature gate activated at the start of epoch 1064, at about 13:36 UTC, but the cluster kept running TowerBFT for the first 5,000 slots, roughly 18 minutes. The last block of that window, slot 459,652,999, became the Alpenglow genesis block. Its genesis certificate carried votes from 446 of the network’s 654 validators, and Alpenglow consensus took over from slot 459,653,000. The Foundation says the handoff itself took about 900 milliseconds.

The same migration ran on testnet and devnet first; the Foundation lists devnet activation on September 25, 2026. Anza’s Alpenglow page now marks the community cluster, testnet, devnet and mainnet-beta stages as completed.

What changed, and what did not

Under TowerBFT, validators voted by sending transactions, and a block became final once enough votes had stacked up over 32 slots. Alpenglow’s voting protocol, Votor, has validators send votes directly to each other and bundle them into certificates, so a block is final after one or two rounds of voting. Votor shipped in Agave 4.3.

The Foundation stresses that execution is untouched: the Solana Virtual Machine, transaction formats, programs and fees stay the same. Signing and sending a transaction works as before, and wallets need no change.

The 150-millisecond figure describes finality, not block production. Block time was cut separately, from 400 to 200 milliseconds, in four stages that the Foundation says completed in October. For the difference between a confirmed transaction and a final one, see our blockchain finality explainer.

Who has to act

The Foundation’s page lists breaking changes for infrastructure rather than for ordinary users:

  • Data streaming. A slot can now carry more than one candidate block, so indexers and services that stream through Geyser or gRPC should buffer by slot and bank ID instead of assuming one block per slot.
  • Commitment levels. confirmed and finalized now describe the same state; new code should read finalized, and confirmed is due to be removed in a later release.
  • Block contents. Vote transactions no longer appear in blocks, so dashboards that counted them will show far fewer transactions without any drop in user activity.
  • Time. Proof of History no longer paces block production, tick entries leave the shred stream and the Clock timestamp gets a new source.

Validators must run an Agave-based client at v4.3.2 (Agave, Jito-Solana or Harmonic Salsa) and keep at least 0.8 SOL in the vote account above its rent-exempt minimum. That balance pays the Validator Admission Ticket, a flat 0.8 SOL fee per epoch that is burned and replaces vote transaction fees. The Foundation says Firedancer and Frankendancer were not supported for the migration.

What comes next

Alpenglow’s second phase, Rotor, would replace Turbine, the protocol that spreads block data across the network. Anza also lists geographically aware leader rotation and Quantumglow, a research design that would swap elliptic-curve signatures for hash-based ones. Anza says these have no committed date.