> ## Documentation Index
> Fetch the complete documentation index at: https://selat.ai/docs/llms.txt
> Use this file to discover all available pages before exploring further.

# Chains

> Where SELAT moves money: the EVM chains you fund on (Circle Gateway), and the rails the router settles merchants on — Circle Gateway nanopayments, Base, Tempo, and Solana.

SELAT separates **where you fund** from **where merchants get paid**. You fund once on an EVM chain into your [Circle Gateway](/docs/primers/nanopayments-gateway) balance; the router then settles each call on whatever rail the merchant accepts. You never manage per-chain balances, and you only ever sign the one Gateway-batched quote — SELAT resolves the outbound chain for you.

## Inbound — funding

Funding is **EVM only**, through **Circle Gateway by default**. You deposit **USDC** into your Gateway balance on any of **7 EVM chains**; Gateway unifies that balance, so funds deposited on one chain are spendable against any settlement rail.

| Fund chain | Network        |
| ---------- | -------------- |
| Arc        | `eip155:5042`  |
| Base       | `eip155:8453`  |
| Ethereum   | `eip155:1`     |
| Optimism   | `eip155:10`    |
| Arbitrum   | `eip155:42161` |
| Polygon    | `eip155:137`   |
| Avalanche  | `eip155:43114` |
| Unichain   | `eip155:130`   |

Depositing is **gasless on every chain** — your Circle Agent Wallet's transactions are gas-sponsored, so you never need ETH or any native token to fund. The [`selat fund`](/docs/selat-cli) `--method` choice is about **speed, not gas**: `--method direct` (the default, any of the 7 chains) settles into Gateway on the chain you fund from with no routing fee (credits typically land in 5–10 minutes), while `--method eco` (from Base today — Eco natively supports Optimism and Arbitrum as well, returning as Circle CLI coverage catches up) uses Eco Fast Deposits to credit in about 30 seconds for a small fixed routing fee, settling into Gateway on Polygon.

<Note>
  **The chain you pay from follows the money.** A Gateway deposit sits on a specific chain — the chain you funded from with `--method direct`, or **Polygon** with `--method eco` — and each payment draws from one of those funded balances. You don't have to track this: a paid run resolves the source chain from your funded Gateway balance automatically (an eco-funded wallet pays on Polygon). Set `CIRCLE_CHAIN` only if you want to pin the source chain yourself.
</Note>

## Outbound — merchant settlement

The **merchant chooses the rail**, and the router translates your single Gateway-batched signature into it. A single funded EVM balance reaches merchants across four settlement targets:

| Rail                              | What settles                                                           | When it's used                                                                         |
| --------------------------------- | ---------------------------------------------------------------------- | -------------------------------------------------------------------------------------- |
| **Circle Gateway** — nanopayments | batched, same-rail Gateway passthrough (no cross-protocol translation) | a Gateway-capable upstream, and sub-cent [nanopayments](/docs/primers/nanopayments-gateway) |
| **Base**                          | [x402](/docs/primers/x402) `exact` — USDC on EVM                            | an x402 upstream on Base                                                               |
| **Tempo**                         | [MPP](/docs/primers/mpp-tempo)                                              | an MPP upstream                                                                        |
| **Solana**                        | [x402](/docs/primers/x402#solana) `exact` — an SPL Token (USDC) transfer    | an x402 upstream on Solana                                                             |

So yes — SELAT pays merchants on **Solana** as well as EVM. **Solana is a settlement chain, not a fund chain**: you still fund and sign on EVM, and the router settles the merchant's leg on Solana (SPL). The same is true of Tempo — you never hold a balance there.

## Related docs

* [Nanopayments powered by Circle Gateway](/docs/primers/nanopayments-gateway)
* [x402](/docs/primers/x402) · [MPP on Tempo](/docs/primers/mpp-tempo)
* [SELAT CLI](/docs/selat-cli) — `selat fund`