Solana's Alpenglow upgrade goes live on devnet as mainnet date stays pending

Alpenglow starts running on Solana's devnet

Solana's Alpenglow consensus upgrade went live on devnet on Sept. 25, according to the Solana software developer Anza. Devnet is a test version of a blockchain that developers use before changes reach the live network.

The switch replaced TowerBFT, the older system Solana used to agree on blocks, on the developer network. Anza said the handoff finished at slot 504,148,999, where Alpenglow's first block was created and TowerBFT was retired. A slot is a time window in which a block can be produced.

Anza asked builders to get involved right away. “App developers: test your programs and integrations now,” the developer wrote.

Faster finality and votes sent off-chain

• Alpenglow targets finality of about 150 milliseconds, compared with about 12.8 seconds under TowerBFT, according to the Solana Foundation's upgrade guide. Finality is the point at which a transaction can no longer be reversed.
• That target applies to settlement, not to how often blocks are produced.
• Alpenglow's Votor protocol replaces votes sent as on-chain transactions with messages sent directly between validators and grouped into certificates. Validators are the computers that run the network and vote on blocks.
• Under the new design, blocks become final after one or two voting rounds, instead of votes building up over 32 slots as before.
• The Solana explorer shows 17 vote transactions in the genesis block at slot 504,148,999 and none in the next child block.

What developers need to test

Transaction formats, execution and fee mechanics are unchanged, the Solana Foundation says. The work falls mainly on applications that read block data or rely on the old confirmation behavior.

For indexers and trading systems that use Geyser or gRPC data streams, the guide says candidate blocks within a slot should be separated using a new field called bank_id. Applications that combine feeds from different providers must match them by blockhash, because bank_id is local to each node.

The confirmed and finalized commitment levels become equivalent after activation. The Foundation advises developers to review timeouts and retry logic that was built around the old finality delay. It also says transaction-count dashboards need adjusting, because validator votes will no longer appear in blocks even though user activity has not fallen.

Latency can also depend on a user's infrastructure. Anza's documentation says nodes outside the admitted validator set may learn about finality through certificates in later blocks, which adds delay compared with receiving Votor messages directly.

Mainnet activation is still pending

The devnet launch followed a testnet handoff on Sept. 24 at slot 444,625,255, also reported by Anza. The Solana Foundation lists both networks as active, with mainnet not yet activated. The rollout continues an upgrade that Solana validators approved last year.

Anza says the move to mainnet-beta, the live Solana network, will come after its observation period. Its feature-gate tracker lists Alpenglow as pending and states that mainnet activations for a new minor software version begin two full epochs after 95% of stake adopts that version.

A tentative Agave v4.3 release schedule targets Sept. 28 for resuming mainnet feature activation. That date covers the release as a whole and is not a confirmed date for the Alpenglow handoff.

What is confirmed

Anza, the primary source here, states that Alpenglow went live on devnet on Sept. 25 and gives the slot where the handoff occurred. Its Sept. 24 testnet handoff and slot number are also reported by Anza. The speed comparison, the technical changes to voting, the developer guidance and the testnet and mainnet status come from the Solana Foundation's upgrade guide and explorer data.

What is still unclear

No mainnet activation date has been announced. The Sept. 28 date in the Agave v4.3 schedule is described as tentative and applies to feature activation across that release, not specifically to Alpenglow. The Foundation's tracker still lists Alpenglow as pending.

Why this matters for Solana users and apps

Finality speed affects how quickly a transaction is treated as irreversible. Applications that depend on confirmation timing, block data feeds or dashboards may need changes before the upgrade reaches the live network. Transaction formats and fees are not affected, according to the Foundation.

Sources

• The Defiant