What is Gulf Stream
Gulf Stream is Solana's mempool-less transaction forwarding protocol. Gulf Stream doesn't just dump pending transactions into a common public mempool like most other chains. Instead, it sends transactions directly to the validators who are going to make the blocks.
Solana publishes the validator schedule an entire epoch (~2 days) in advance. This means wallets, RPC providers, and validators all know who is going to be building the block 400ms from now. To put it another way: it's like sending a package. With most other chains, you drop it at the central depost and wait for whoever is next on the sorting list. With Gulf Stream you send it straight to the driver that is going to be leaving in the next batch. No depot, no queue, no sorting needed.
How Gulf Stream Works Technically
Solana creates a deterministic, stake-weighted leader schedule every epoch. This assigns each validator a specific slots to create blocks. A leader produces 4 consecutive slots of 400ms each before yielding the leader role to the next validator. The schedule is public. Therefore, transaction routing is simple.
If you swap on Jupiter through Phantom, your wallet sends the transaction to the RPC node of an RPC provider like Helius. Helius then forwards the transaction to the leader for the upcoming slot, along with the next several upcoming leaders. If the current slot fills up, the next leader will have the transaction available.
Transactions have an expiry as well. All transactions point to a recently seen blockhash, which expires after approximately 150 blocks (roughly a minute). Any transactions that are "expired" just die, which is how Solana can avoid the multi-gigabyte mempool that other chains end up filling up with when they are congested.
How Gulf Stream Compares to Ethereum's Mempool
Ethereum has a public mempool, which means all pending transactions are visible to the public. It's what makes sandwich bots so viable: a sandwich bot sees your transaction waiting in the mempool, buys ahead, lets your transaction bump the price, then sells into you. Users also bid against each other for gas during times of high congestion. At the peak of congestion, users were paying $50-$500 to get a single swap through.
Gulf Stream eliminates the need for a public mempool, there is no global mempool to front-run transactions in. Users also don't need to bid against other for transactions. The base fees remain around $0.00025.
However, fairness hasn't been completely achieved. MEV (the profit gained from reordering transactions), can still be extracted through leaders and through infrastructure like Jito's transaction bundle auctions. However, this extraction happens at a leader level rather than a pool of transactions, which limits some of the more exploitable opportunities.
One unintended benefit of Gulf Stream making it so cheap and easy to forward transactions to a leader is that it makes spam really cheap, as well. One of the main reasons for congestion in the 2022 to 2024 timeframe was bots spamming millions of duplicate transactions to a leader when there was a hot NFT mint.
The solution Solana introduced was stake-weighted quality of service. Stake-weighted quality of service gives priority to connections that have stake, and allows leaders to reserve bandwidth specifically for transactions with priority fees.
Why Gulf Stream Matters
Gulf Stream is the reason that on Solana it feels like the transactions execute instantly. Transactions execute as soon as they reach the next leader, before the previous block has even finished confirming. Users benefit with a swap that executes in a second and no fee auctions. Validators benefit by having predictable memory consumption, as transaction's don't have an unlimited lifetime. And developers building trading applications on DEXs such as Drift or Kamino can have low enough latency to allow them to have profitable trading strategies that would never make the cut with an Ethereum mempool.
Does Gulf Stream eliminate frontrunning on Solana?
No, there is still some amount of frontrunning that is possible on Solana. Since transactions go directly to leaders before execution, leaders still have an advantage, although there is Jito running block building with MEV auctions as well.
But Gulf Stream does take away the public mempool, eliminating the most accessible and exploitable front-running surface for sandwich attacks that Ethereum users are all too familiar with.
