Post-Pack Confirmations
Rakurai pre-confirmation (P2C) is a stream of transactions sent by validators when a transaction reaches the point of no return: early enough to act on, late enough that nobody can front-run the original sender. Each transaction is sent only once (duplicates are suppressed).
It is the third TIN building block. You can resell, backrun, or both.
Audience: Searchers, TIN partners, traders consuming post-pack confirmations, and validator operators configuring endpoints.
Related: Using P2C · PSA · MCA · Setup guide · Tips
Resell (selling pre-conf) — monetize orderflow by selling post-pack access to searchers and traders.
- PSA — You pay an epoch fee by volume: $50 / 1M txn Updates, dollar equivalent amount in SOL.
StartExpiringPacketStream— Receive post-pack confirmations for resell / pre-conf.
Backrun — consume the stream and submit reply bundles for profit.
- MCA — Pre-conf is free if you share backrun through an MCA (65% of backrun profit). Record and settle after each epoch.
StartExpiringMevPacketStream— Post-pack confirmations after the point of no return (front-run protected).StartExpiringTpuPacketStream— Optional TPU packets when the validator is not the leader (not front-run protected).
If you sell and backrun, both apply: PSA fees on sold updates, and 65% of backrun profit through the MCA. Tips are separate. See Tips.
1. What are post-pack confirmations?
As soon as a transaction is scheduled for execution, the Rakurai scheduler forwards it over gRPC to every configured post-pack endpoint — one packet per transaction, per endpoint.
A post-pack confirmation is emitted when the transaction is committed to the block being built. You see it early enough to act, but too late for anyone to front-run the sender. It is an early scheduled update, not final confirmation — confirm landing with standard commitment checks.
1.1. Protocol
Post-pack uses the TIN / P2C gRPC packet protocol (packet.proto, block_engine.proto) — wire-compatible with Jito Packet / PacketBatch shapes.
| Piece | Detail |
|---|---|
| Resell stream | StartExpiringPacketStream when resell (no-boost hash; no TPU) |
| Backrun stream | StartExpiringMevPacketStream when mev (boost-eligible hash) |
| TPU stream (optional) | StartExpiringTpuPacketStream when mev + enable_tpu_p2c_update. Same wire type — tell streams apart by which gRPC method delivered the message |
| Count stream (optional) | StartP2cUpdateCountStream — once per slot, counts for post-pack confirmation and TPU streams |
| Discovery | GetBlockEngineEndpoints on the P2C host (same discovery RPC as bundles) |
expiry_ms | Validator working-bank slot (u32) on the P2C path — not a millisecond timeout |
| Reply | Bundle with original post-pack packet(s) unchanged, plus your txs. Post-pack Mev sources get 20% virtual priority when tipped at the Minimum Tip Requirements |
You can enable resell, mev, or both on the same endpoint (two scheduler connections with distinct hashes when both are on). Full mechanics: Using P2C. Setup: Setup guide — P2C / BlockEngineRelayer.
1.2. End-to-end sequence
| Step | Action | Guide |
|---|---|---|
| 1 | Register a gRPC discovery endpoint with Rakurai | Setup guide |
| 2 | Choose sell (PSA), backrun (MCA; pre-conf free), or both | PSA · MCA |
| 3 | Fund PSA if you sell; hold MCA record_authority if you backrun | rakurai-p2c · rakurai-revshare |
| 4 | Validator connects out to your Relayer server | Using P2C |
| 5 | Consume the stream; reply with bundles when applicable (original packets + your txs + a tip) | Tips |
| 6 | Epoch ends → PSA fee (if selling) and/or MCA record + transfer (if backrunning) | CLI docs above |
Paying a tip is separate from the PSA and MCA. A reply bundle still needs a tip to a Rakurai tip account.
- P2C MEV: 0.001 SOL — Minimum tip to receive the 20% virtual priority boost on P2C MEV bundles. A lower tip may result in reduced QoS and no priority boost.
- Non-P2C: 0.0005 SOL — Recommended tip for regular non-P2C bundles to get the best QoS. Lower tip may lead to potentially lower QoS.
- Below 100K lamports: Bundles with low tips are processed on a best-effort basis.
2. Access and payments
How you pay depends on what you do with pre-conf:
| What you do | How you pay |
|---|---|
| Backrun only (share through MCA) | Pre-conf is free. Share 65% of backrun profit via the MCA. No PSA. |
| Sell / resell pre-conf | Pay through a PSA — epoch fee by volume ($50 / 1M txn Updates, dollar equivalent amount in SOL). |
| Sell and backrun | Both of the above: PSA fee on txn Updates, and 65% of backrun profit via the MCA. |
PSA and MCA are different accounts for different products. Tips (TCA) are separate and still apply to reply bundles.
| PSA | MCA | Tips (TCA) | |
|---|---|---|---|
| Full name | P2C Subscription Account | MevShare Collection Account | Tips Collection Account |
| Use when | Selling / reselling pre-conf | Backrun / MevShare | Landing priority on a tx or bundle |
| What you pay | Epoch fee by volume ($50 / 1M txn Updates, dollar equivalent amount in SOL) | 65% of backrun profit (pre-conf access included) | Whatever you tip |
| Streams | Post-pack confirmation (resell) | Post-pack confirmation (mev) + optional TPU | — |
| Tool | rakurai-p2c | rakurai-revshare | SystemProgram.transfer |
| Guide | PSA | MCA | Tips |
- Sell only — fund a PSA. Enable
resell. - Backrun only — settle through an MCA (pre-conf free). Enable
mev(and TPU if needed). No PSA. - Sell and backrun — fund a PSA for sold updates, and settle 65% of backrun profit through an MCA. Enable both
resellandmev.
Tips on reply bundles are always separate.
Endpoints (where the scheduler sends you transactions) live in Client Config. The PSA holds SOL for epoch volume fees; the MCA holds settled backrun SOL. Neither holds endpoint config.
If block_reward_conversion_enabled is on (the default), PSA, MCA, and TCA claims are later re-emitted as a high-priority block reward. An indexer watching both will count the same lamports twice. See TIN — indexing note.
3. Next steps
| Guide | Description |
|---|---|
| Using P2C | Relayer gRPC, packets, reply bundles, Admin RPC |
| PSA | Resell access: epoch volume pricing, status, grace window, funding |
| MCA | Reporting and settling your backrun share |
| Tips | Tip accounts and virtual priority |
| Setup guide | Discovery endpoint and Validator vs Relayer gRPC roles |
| Reward Distribution | On-chain model behind PSA, MCA, and TCA |