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

# Core concepts

> Understand Stable's four core concepts before you build: USDT0 as gas, guaranteed blockspace, transfer aggregation, and EVM compatibility.

Four concepts are enough to start building. Each section defines the concept, shows it, and links to the full reference.

## USDT0 as gas

You pay transaction fees in USDT0, the same asset you're already holding and transacting in. There's no second token to fund or manage.

USDT0 is both the native gas asset (18 decimals, read via `address(x).balance`) and an ERC-20 token (6 decimals, read via `USDT0.balanceOf(x)`). Both interfaces operate on the same underlying balance, and the protocol reconciles the 12-digit precision gap automatically.

```solidity theme={"dark"}
// Both read the same balance:
uint256 native = address(user).balance;        // 18 decimals
uint256 erc20  = IERC20(USDT0).balanceOf(user); // 6 decimals
```

<Warning>
  Balance reconciliation emits extra `Transfer` events at the reserve address `0x6D11e1A6BdCC974ebE1cA73CC2c1Ea3fDE624370`. Indexers that replay `Transfer` events must filter transfers to and from this address, or they will silently double-count balances.
</Warning>

Read more: [USDT0 as gas](/en/explanation/usdt-as-gas-token) · [USDT0 behavior on Stable](/en/explanation/usdt0-behavior).

## Guaranteed blockspace

Stable reserves a portion of each block's capacity for pre-allocated enterprise workloads. Reserved traffic settles with predictable latency and cost even when general traffic is congested; it doesn't compete in the fee market.

This behavior is transparent at the caller level. You submit transactions the normal way; allocations are applied at the protocol level for enrolled accounts.

Read more: [Guaranteed blockspace](/en/explanation/guaranteed-blockspace).

## USDT transfer aggregator

High-volume USDT0 transfers are batched and verified in parallel using a MapReduce-inspired pipeline. Per-account failures are isolated, so one bad transfer doesn't abort the batch.

The caller-side transfer API is unchanged. You submit transfers the normal way and gain throughput without code changes.

Read more: [USDT transfer aggregator](/en/explanation/usdt-transfer-aggregator).

## EVM compatibility

Standard EVM tooling works unchanged. At the EVM level, three behaviors differ from Ethereum (USDT0 as gas, covered above, is the fourth).

**Single-slot finality.** A transaction is final once included in a block. Blocks are produced roughly every 0.7 seconds.

**No priority tips.** `maxPriorityFeePerGas` is always ignored. The effective gas price is the base fee set by the protocol.

```typescript theme={"dark"}
import { ethers } from "ethers";

const block = await provider.getBlock("latest");
const baseFee = block.baseFeePerGas;

const tx = await wallet.sendTransaction({
  to: "0xRecipientAddress",
  value: ethers.parseEther("0.1"),
  maxFeePerGas: baseFee * 2n,        // 2x base fee as safety margin
  maxPriorityFeePerGas: 0n,          // always 0 on Stable
});

await tx.wait();
console.log("Included at gas price:", tx.gasPrice?.toString());
```

```text theme={"dark"}
Included at gas price: 1000000000
```

**Dual-role USDT0, porting risks.** Contracts ported from Ethereum should not mirror native balance, should reject `address(0)` transfers, and should not rely on `EXTCODEHASH` for address-reuse detection.

<Warning>
  Porting a contract that mirrors native balance in an internal variable is unsafe on Stable. An external `USDT0.transferFrom` call can drain the contract's native balance without invoking any contract code. Always solvency-check with `address(this).balance` at the moment of transfer.
</Warning>

Read more: [Differences from Ethereum](/en/explanation/ethereum-comparison) · [Contracts on Stable](/en/explanation/contracts-overview) · [USDT0 migration checklist](/en/explanation/usdt0-behavior).

## Confidential transfer (planned)

Stable has a planned feature for zero-knowledge transfers that hide amounts while staying auditable for authorized parties. It is not yet live.

Read more: [Confidential transfer](/en/explanation/confidential-transfer).

## Next recommended

<CardGroup cols={2}>
  <Card title="Quick start" icon="rocket" href="/en/tutorial/quick-start">
    Connect to testnet and send a first transaction.
  </Card>

  <Card title="USDT0 behavior" icon="split" href="/en/explanation/usdt0-behavior">
    Port a contract to Stable without hitting dual-role gotchas.
  </Card>

  <Card title="Gas pricing" icon="fuel" href="/en/reference/gas-pricing-api">
    Construct transactions correctly on Stable's fee model.
  </Card>

  <Card title="Production readiness" icon="shield-check" href="/en/how-to/production-readiness">
    Validate an integration before shipping to mainnet.
  </Card>
</CardGroup>