A “Level 1 chain” is almost always called a Layer 1, or L1. It is the main, base blockchain in a multi-level network: the chain that other networks are built on and that they ultimately settle to. Bitcoin and Ethereum are the standard examples.
What the term means
Ethereum.org’s glossary gives the working definition:
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“Layer 1 refers to the main blockchain in a multi-level blockchain network.”
PerformancePC Slower Than It Used to Be?DriversOutdated Drivers Are Slowing You DownPerformanceWindows Errors? Fix Them Before They SpreadSpecial offer. See more information about Outbyte and uninstall instructions. Please review EULA and Privacy policy.— Ethereum.org glossary (documentation text, not an individual’s quotation)
A blockchain is a public database shared and updated across many computers. Each block cryptographically references the blocks before it, and the nodes that maintain the chain agree on new blocks and on the chain’s overall state. That consensus-maintained base is what the “Layer 1” label points to. Everything built on top of it depends on it for final agreement.
Why “Level 1” is written “Layer 1” or “L1”
“Level 1” is a literal rendering of the same idea. In blockchain documentation and industry writing, the standard forms are “Layer 1” and “L1.” If you encounter “Level 1 chain” in a document, read it as a base blockchain. The numbering only signals position in a stack: the base is 1, and networks that run on top of it are described as Layer 2 or higher.
Examples of Layer 1 networks
| Network | Role as a Layer 1 | Qualification |
|---|---|---|
| Bitcoin | Listed as an example of a Layer 1 blockchain in the Ethereum.org glossary. | The glossary gives it as an example; it does not describe Bitcoin’s internal design. |
| Ethereum | Listed as a Layer 1 blockchain, and the base layer for the Ethereum rollups described in Ethereum.org’s scaling documentation. | Its rollups are Layer 2 networks that depend on Ethereum for settlement and data. |
How Layer 2 networks depend on Layer 1
A Layer 2 network is built on top of a Layer 1 to help it scale. The base chain stays the reference point, and the Layer 2 handles more of the work. Ethereum.org’s description of rollups follows this pattern:
- Transactions are executed outside Layer 1.
- Data about those transactions is posted to Layer 1.
- Layer 1 reaches consensus on the posted data, which is what gives the Layer 2 its final footing.
For optimistic rollups specifically, Ethereum smart contracts on Layer 1 manage rollup blocks, state updates, and deposits. Computation and state storage happen on a separate virtual machine. Ethereum therefore acts as the base layer for these rollups, even though most of the activity happens elsewhere.
Borderline cases: the validator-set test
The general glossary definition is broad: the main blockchain in a multi-level network. Some technical contexts add a sharper criterion. In the Ethereum Layer 2 interoperability nomenclature, a Layer 1 is a blockchain that relies on its own validator set for its security and consensus properties. This matters when a network’s Layer 1 status is disputed, or when a scaling network’s security is unclear.
When you need to classify a chain, check these three points:
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- Consensus: which validators or nodes agree on new blocks?
- Security: does the chain’s own validator set secure it, or does it inherit security from another network?
- Settlement: if the network is a scaling layer, which chain does it post data to and settle on?
Terminology is not applied identically across every project. Two projects may both call themselves Layer 1 while meaning different things by the term, so define the relationship a chain has to other networks rather than relying on the label alone.
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What to compare between Layer 1 networks
If you are comparing actual Layer 1 networks rather than defining the term, the relevant axes are:
- The security and consensus model, including the validator set.
- Decentralization.
- Transaction speed and throughput.
- How scaling approaches, such as Layer 2 rollups, interact with the base chain.
Ethereum.org names speed, throughput, decentralization, and security as the main scaling trade-offs. The definition itself does not rank Layer 1 networks, and the documentation reviewed does not establish a current, comprehensive ranking. Performance figures for any network change with protocol upgrades, so check current data before drawing conclusions.
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