'Helius Launches preprocessedSubscribe: Stream Pre-Execution Solana Transactions

Helius hSOL$124.18-1.8% launched preprocessedSubscribe in public beta on August 28, delivering a WebSocket method that streams decoded Solana transactions before they reach the processed commitment level. The endpoint requires no raw shred handling, no deshredding infrastructure, and no gRPC client.

The new method also replaces the earlier gRPC delivery route for preprocessed transactions, which Helius plans to deprecate. Where the legacy gRPC option was restricted to Professional plan subscribers, preprocessedSubscribe is available across all paid plans at 0.1 credits per transaction delivered.

Where preprocessedSubscribe Sits in Solana's Transaction Lifecycle

Solana moves a transaction through five stages before it becomes fully committed: shred reception, shred decoding, execution, metadata generation, and commitment. Standard post-execution subscriptions, including LaserStream gRPC and LaserStream WebSocket, deliver data at stage 5, after balance changes and program logs have been computed.

preprocessedSubscribe delivers at stage 2: after Helius has decoded the incoming shreds but before the Solana runtime has executed the transaction. Helius aggregates shred-decoded data with its Preconfirmations signals into a single deduplicated stream, though transactions sourced from preconfirmation signals arrive later on this feed than on the dedicated Preconfirmations product.

For applications where stage-2 timing matters, this eliminates what had previously been the entry barrier: operating a deshredding stack at line rate.

What Each Binary Frame Contains and What It Does Not

Each message is a compact binary frame carrying the slot number, the transaction signature, and the full signed transaction. Available fields include account keys, all instruction data, the recent blockhash, and all signatures.

What is absent is everything generated during execution: token balance changes, pre- and post-balances, error information, inner instructions from cross-program invocations, program log messages, and compute units consumed. Helius describes the distinction as receiving the proposal without the result: you see what the sender intended, not what the runtime did with it.

Delivery is best-effort, with no historical replay. A transaction on this feed can fail, be dropped, or land on a different fork. Helius recommends deduplicating by signature and reconciling against a processed stream when execution outcomes matter.

Account Filters in preprocessedSubscribe: Include, Exclude, Required, and Lookup Tables

preprocessedSubscribe supports server-side account filters with include, exclude, and required modes, and those filters also match against accounts resolved through address lookup tables. Filtering at the server rather than the client means applications receive only the transactions relevant to the accounts they track, rather than processing the full network stream locally.

The announcement thread notes the recommended workflow for latency-sensitive use: deduplicate incoming transactions by signature, then pair with Helius Sender to land transactions ahead of competition.

preprocessedSubscribe Pricing: 0.1 Credits Per Message on All Paid Helius Plans

The WebSocket method is available to all paid Helius plans at 0.1 credits per message, one message per delivered transaction. The legacy gRPC delivery it replaces was priced at 2 credits per 0.1 MB of uncompressed streamed data and gated to Professional subscribers.

The shift from data-volume billing to per-transaction billing makes cost more predictable for applications running account-filtered subscriptions: cost scales with transactions received rather than raw bytes on the wire.

For applications that need processed-commitment data with execution metadata, or real-time account and program state updates, Helius recommends LaserStream gRPC at processed commitment instead. preprocessedSubscribe is a transactions-only stream. Account and program state does not exist at stage-2 timing.

preprocessedSubscribe Use Cases: MEV Bots, Snipers, Copy Traders, and Arbitrage

Helius positions the feed for latency-sensitive applications that need decoded pre-execution transactions without building shred handling: propAMMs, snipers, copy traders, liquidation bots, and arbitrage systems. The documentation is direct: if every microsecond matters and you can deshred at line rate, raw shreds over UDP remain faster. If that infrastructure overhead is the barrier, preprocessedSubscribe is the alternative.

The rpc-perf-dash benchmark tool Helius open-sourced in July added continuous cross-region RPC performance measurement. preprocessedSubscribe extends that work into pre-execution transaction data access, opening a class of Solana applications that previously required running full deshredding pipelines to teams on any paid tier.

Full documentation is at helius.dev/docs/preprocessed-transactions/overview.