How the chain works today

This page follows one transaction through Solana as the network ran on 2 October 2026, from the moment a wallet signs it to the point where it can no longer be rolled back. Every measured number below was read from the public mainnet RPC that day, around 15:17 UTC ¹.

Slots, epochs and leaders

Solana divides time into slots. Since September 2026 the target slot has been 250 ms, and the measured average on 2 October was about 263 to 269 ms per slot ¹². Each slot has one scheduled leader, the validator allowed to produce a block in it. Leaders hold four consecutive slots, so one leader window lasts about a second ². An epoch is 432,000 slots, roughly 32 hours at the current pace ¹².

The leader schedule for each epoch is computed in advance from a seed and the stake of the active validators, so validators with more stake lead more often, and the order is known ahead of time ³. While it leads, a validator runs the Proof of History hash chain and builds its block on that clock, 64 ticks per slot ²⁶.

From wallet to leader

A transaction carries signatures, a header, the list of every account it will touch, a recent blockhash and its instructions. The header marks each account as signer or not, and as writable or read-only. The whole transaction must fit in 1,232 bytes, or 4,096 bytes in the v1 format that went live on 15 September 2026 ⁴⁵.

Solana has no global mempool. A wallet hands the transaction to an RPC node, which forwards it to the current or upcoming leader, the idea the 2019 design called Gulf Stream ⁶. The leader's transaction processing unit receives transactions over QUIC and caps connections and streams per sender, allowing more streams to senders with more stake. It removes duplicates, drops invalid signatures and, while the node leads, executes transactions into a block ⁷.

Parallel execution

Because every transaction lists its accounts and says which ones it writes, the runtime can find transactions that touch different state and run them at the same time on different cores. The 2019 design called this Sealevel ⁴⁶.

Work is metered in compute units; a transaction may request up to 1.4 million ⁸. At today's 250 ms slot a block may hold 62.5 million compute units, and no single writable account may take more than 25 million ⁹. That block limit is the 100-million-unit limit set for 400 ms slots on 29 July 2026, scaled down with the slot so capacity stays at 250 million per second, as SIMD-0525 requires ²⁵⁹.

Spreading the block

The leader cuts its block into small packets called shreds, adds erasure-coded recovery shreds so lost packets can be rebuilt, signs them and sends them through Turbine ⁷¹⁰. Each shred goes first to a root node, then to a layer of validators, each of which passes it to a fixed number of nodes in the next layer. The tree is reshuffled for every shred using a stake-weighted ordering, which makes attacks on the propagation path harder ¹⁰. Validators reassemble the block, replay its transactions and vote on it.

Votes and commitment

An RPC node reports a transaction at three commitment levels ¹¹¹:

• processed: the node has the block on the majority fork, and it can still be rolled back.
• confirmed: validators holding more than two-thirds of stake have voted on the block.
• finalized: at least 31 confirmed blocks have been built on top of it.

On 2 October 2026 the confirmed slot trailed the processed slot by about one slot, and the finalized slot trailed it by 32. Finality therefore took about 8.5 seconds, while a new block arrived roughly every 265 ms ¹. Alpenglow, a replacement consensus not yet on mainnet, would make confirmed and finalized mean the same thing ⁵¹¹.

Fees

Every signature costs a base fee of 5,000 lamports, half burned and half paid to the validator ⁸. A transaction can add a priority fee, the compute-unit price in micro-lamports times the compute-unit limit it requests, and the validator receives all of it ⁸. That full payout has applied since SIMD-0096 activated on 12 February 2025 ⁵. Transactions in the v1 format state the priority fee as a total in lamports instead ⁸.

The clients

Anza, a company formed by former Solana Labs executives and engineers, forked the Solana Labs validator into Agave on 2 March 2024 ¹². Jito maintains Jito-Solana, its fork of the validator, which takes bundles and packets from Jito's block engine ¹³¹⁴. BAM, Jito's Blockspace Assembly Marketplace, adds a BAM node that validates and sequences transactions and hands them to the leader, which must execute them in that exact order. It runs on Jito-Solana as AgaveBam or on Firedancer as FireBAM ¹⁴¹⁵.

Firedancer, built by Jump Crypto, is a validator written from scratch with no Agave code. Frankendancer is the hybrid: Firedancer's networking and block production with Agave's execution and consensus ¹²¹⁶. The Foundation's Breakpoint 2025 recap announced Firedancer officially on mainnet ¹⁵.

On 2 October 2026, 672 validators were voting and 12 more were delinquent. Each node reports a client label through gossip, and weighting those labels by active stake gives this picture ¹:

Builds labelled HarmonicAgave and HarmonicFiredancer held 18.5% and 6.9%, and Rakurai and Raiku builds held 1.4% and 0.1% ¹. Counting every Firedancer-based label, 15.6% of active stake ran Firedancer code ¹¹⁴.

Sources

1. Solana JSON-RPC, mainnet readings of 2 October 2026: commitment levels, and slot time, lag, epoch, validators, client labels
2. SIMD-0525, Reduce Slot Times: slot target, leader windows, epochs, ticks, scaled limits
3. Agave docs, leader rotation: stake-weighted leader schedule
4. Solana docs, transaction structure: header, account list, size limits
5. Agave feature gates, read on mainnet 2 October 2026: v1 transactions, 100M limit, SIMD-0096, Alpenglow gate absent
6. Yakovenko, "8 Innovations" essay, 2019: Gulf Stream, Sealevel
7. Agave docs, transaction processing unit: QUIC, stake-based limits, broadcast
8. Solana docs, fees: base fee, burn, priority fee, compute limit
9. Agave source, slot parameters: 62.5M block and 25M account limits at 250 ms
10. Agave docs, Turbine: shreds, layers, reshuffling
11. Agave docs, commitment status: the three levels, Alpenglow
12. Anza on the Agave fork, March 2024: Agave fork, Jump builds Firedancer
13. Jito-Solana repository: Jito's validator fork
14. BAM documentation: BAM node, block engine, AgaveBAM, FireBAM
15. Solana Foundation, Breakpoint 2025 recap: Firedancer on mainnet, BAM from Jito
16. Firedancer repository: Firedancer and Frankendancer defined