# Fast by Circular — FAQ

> Land your Solana transactions in the current slot, 0-slot delay, and earn back 65% of the value they leak, paid in SOL.

Source: https://landfast.io · Docs: https://docs.circular.fi/api/fast

## What is Fast?

Fast is Circular's transaction broadcast service for Solana. When you submit a raw transaction, Fast races it over several independent routes at once, Solana nodes, dedicated SWQoS connections, UDP routes, Jito, Harmonic, Rakurai and private validator deals, so it lands in the current slot. Once it has landed, Fast monetizes the value your transaction leaves on the table and pays 65% of it back to your cashback address in SOL. Your transaction itself is never modified.

## What does 0-slot landing mean?

Solana slots are 200ms long. A standard RPC usually gets your transaction in too late, so it is queued for the next slot, 200ms behind. Fast propagates wide enough and fast enough to land in the slot that is already open, which is what 0-slot means: zero slots of delay between sending and landing.

## How does the 65% cashback work?

Your trade moves the price of a pool, so it leaves value on the table. On any other RPC a third party captures that value and keeps all of it. Fast captures it on your own transaction, after it has landed, and sends 65% of it in SOL to the cashbackAddress you include in your request. The remaining 35% covers execution and validator costs. There is nothing to claim and no extra API call.

## Do I have to set a cashback address?

It is optional but recommended: no cashbackAddress means no cashback to route. Pass any Solana address you control, including one different from the signer, and the SOL is credited there.

## How do I get an API key?

API keys are managed through the Circular dashboard. Visit docs.circular.fi/api/keys to create and manage your keys. Each key is tied to a subscription tier that determines your rate limits.

## What are the rate limits per tier?

Fast supports multiple tiers: Free (25 RPS), Searcher (50 RPS), Startup (100 RPS), and Pro (150 RPS). All tiers use the same endpoint and the same JSON-RPC format. Only the throughput ceiling changes.

## Can I use Fast alongside Jito bundles?

Yes. Fast and Jito bundles serve different purposes. Fast optimizes individual transaction propagation. Jito bundles allow you to submit ordered groups of transactions atomically. You can use Fast to broadcast your non-bundle transactions while still submitting bundles directly through the Jito block engine.

## Is my existing sendTransaction code compatible?

Yes. Fast uses the standard JSON-RPC 2.0 sendTransaction method. The only changes are the endpoint URL (fast.circular.fi/transactions) and the addition of the x-api-key header. The params array accepts Base58 or Base64 encoded transactions, just like any Solana RPC.