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## `setEvmVersion`

### Signature

```solidity
function setEvmVersion(string calldata evm) external;
```

### Description

Sets the execution EVM version for subsequent calls and contract creations in the current test or script, e.g. `"berlin"` or `"cancun"`. Hardfork-dependent cheatcodes use the new version on their next call.

The currently executing call frame keeps its original opcode rules. To test an opcode under the new version, make an external call after changing the version.

This changes only the execution EVM version. The contracts are not recompiled, so the compilation EVM version stays the one set by `evm_version` in `foundry.toml` or `--evm-version`.

### Parameters

| Parameter | Type     | Description                                     |
|-----------|----------|-------------------------------------------------|
| `evm`     | `string` | The EVM version name, in lowercase (e.g. `"cancun"`) |

### Examples

```solidity [test/SetEvmVersion.t.sol]
// [!include ~/snippets/projects/evm_version/test/SetEvmVersion.t.sol]
```

```bash
$ forge test --root src/snippets/projects/evm_version --match-contract SetEvmVersionTest --evm-version cancun
```

### Gotchas

Use lowercase Ethereum hardfork names for compatibility across Foundry versions. Some releases reject `"Cancun"`, while newer nightly releases accept it. An unsupported name reverts with `invalid evm version <name>`.

:::warning
Switching to an older hardfork can make compiled bytecode fail with `NotActivated` if it uses opcodes introduced by a later hardfork. Compile contracts for the oldest hardfork you intend to execute them under.
:::

### Related Cheatcodes

* [`getEvmVersion`](/reference/cheatcodes/get-evm-version) - Gets the execution EVM version