# Ethereum Data Model

The [sf.ethereum.type.v2.Block](https://github.com/streamingfast/firehose-ethereum/blob/develop/proto/sf/ethereum/type/v2/type.proto#L51) Protobuf is shared across EVM-compatible blockchains (Ethereum, Polygon, Arbitrum...). While the Protobuf definition (`.proto` file) is largely self-documented, it is important to be aware of the **version** of the Protobuf you are working with.

## The Protobuf Version

Most changes in EVM chains are backward-compatible, meaning there is no need to introduce an entirely new Protobuf namespace (e.g., *sf.ethereum.type.v3.Block*). Instead, `sf.ethereum.type.v2.Block` is used consistently to avoid breaking changes.

To manage internal updates, Firehose uses a versioning system defined by the `ver` [field](https://github.com/streamingfast/firehose-ethereum/blob/develop/proto/sf/ethereum/type/v2/type.proto#L132) in the `Block` Protobuf.

```rust
// Ver represents that data model version of the block, it is used internally by Firehose on Ethereum
// as a validation that we are reading the correct version.
int32 ver = 1;
```

This version refers to the `Block` emitted by the Firehose trace.

### Version 3

* This version is current in place for **all EVM chains, with the exception of Optimism** from block 0 to the last pre-Prague (blockchains currently in Prague version are listed in a section later in this document) hard fork block.
* This version contains several known issues, which are described in the Protobuf definition itself (next to the corresponding field affected). You can also check out [this GitHub issue](https://github.com/streamingfast/firehose-ethereum/issues/71).

### Version 4

* This version is currently in place for the following chains:
  * Optimism
  * Ethereum Hoodi
  * Sei EVM
* This version fixes the known issue of version 3.

## Prague-enabled blockchains

The following chains have already upgraded to Ethereum's Prague version:

* Ethereum Sepolia
* Ethereum Holesky
* BSC Mainnet
* BSC Testnet


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