--- title: "What are Ethereum commitment levels?" description: "Learn About Safe (Justified), Finalized, and Latest Commitment Levels" --- # What are Ethereum commitment levels? The [Beacon Chain](https://www.alchemy.com/overviews/what-is-the-ethereum-beacon-chain) introduces two new Ethereum commitment levels, _safe_ and _finalized_, that are used to label blocks alongside the existing _latest_, label from the PoW chain. The _latest_ block tag is the most recent block to be added to Ethereum's blockchain, also known as the "head," the _safe_ commitment level is one epoch \(i.e. 32 slots\) behind the current epoch, and the _finalized_ commitment level is one epoch behind the most recently marked _safe_ block. Ethereum commitment levels are helpful because they offer useful primitives for web3 developers to query unlikely-to-[reorg](https://www.alchemy.com/overviews/what-is-a-reorg) blocks enabled by Ethereum’s Proof-of-Stake algorithm changes.  Because developers have higher guarantees that _justified_ and _finalized_ blocks are unlikely to be reorged, they can build stronger assumptions into their smart contracts and decentralized applications. ## **What is a block number?** **The block number is a numerical value used to designate the order of a block added to the blockchain.** For example, if the pending block being built and validated has a block number of 100, the most recently validated block \(i.e. the _latest_ block\) would have a block number of 99.  ## **What is a chain re-organization \(re-org\)?** A [**chain re-organization**](https://www.alchemy.com/overviews/what-is-a-reorg) is when a block that was added to the canonical chain (i.e. main chain, or longest chain) is removed and replaced by a different block. Reorgs impact settlement finality because blocks added to the canonical chain can be changed through a reorg. Because reorgs can happen from exploits and as a result of [Maximal Extractable Value \(MEV\)](https://www.alchemy.com/overviews/what-is-mev), trusting that the latest block is settled is a difficult assumption for developers to make.  With the migration from Proof-of-Work to Proof-of-Stake, Ethereum’s Beacon chain introduced _safe_ and _finalized_ block commitment levels to provide developers with stronger guarantees. ## **What is an epoch?** **In the post-merge Ethereum environment, the Beacon Chain introduces slots, which are opportunities for new blocks to be built, and epochs which are equal to 32 slots.** Because a new block can be validated exactly every 12 seconds, an epoch is equal to 6.4 minutes. During each epoch, the Beacon Chain randomizes a committee of validators to attest to the validity of blocks being added to the blockchain. The _safe_ and _finalized_ block commitment levels are determined based on epochs. While there are [32 slots in each epoch](https://ethereum.org/en/developers/docs/data-and-analytics/block-explorers/#consensus-layer-data), on rare instances \(less than 1%\), a block might not get validated in every slot, so some epochs may have less than 32 blocks. One example is if the randomly chosen validator is not online. ## **What are Ethereum commitment levels?** [**Ethereum commitment levels**](https://www.alchemy.com/docs/how-to-get-the-latest-block-on-ethereum) are tags used to label validated blocks as either latest, justified, or finalized, which offers developers certain guarantees with regards to how likely the blocks will be reorganized. ### **1. Latest** ‍The _latest_ block is the most recent block to be built and validated by Ethereum validators. The _latest_ block should be used with caution because there are no guarantees that the Beacon Chain will not get reorganized, and this block becomes an Uncle Block, or [a block that was not added to the canonical chain](https://www.alchemy.com/docs/what-are-uncle-blocks). ### **2. Safe** ‍The _safe_ block is a block that has received attestations from two-thirds of Ethereum’s validator set. _Safe_ blocks are understood as unlikely to be reorged.  For example, one of the few ways _safe_ blocks could experience a chain reorganization is if there is a large-scale, coordinated attack on the network. ### **3. Finalized** A finalized block is a justified block that is 1 epoch behind the most recently _justified_ block. _Finalized_ blocks are extremely [unlikely to be re-organized](https://blog.ethereum.org/2021/11/29/how-the-merge-impacts-app-layer), with the only exception being if a two-thirds majority of validators finalize a competing chain of blocks. ## How are safe and finalized commitment levels determined? Safe and finalized commitment levels are determined by the completion of epochs. Let’s imagine the first three epochs \(epoch 0, 1, and 2\) after The Merge to visualize how safe and finalized blocks work. - Epoch 0 = blocks 0-31 - Epoch 1 = blocks 32-63 - Epoch 2 = blocks 64-95 - Epoch 3 = blocks 96-127 Let’s assume the latest block is block 96, which marks the beginning of epoch 3 and the end of epoch 2. Because block 96 includes [attestations](https://www.paradigm.xyz/2021/07/ethereum-reorgs-after-the-merge) \(i.e. votes from validators that signal the [proposed canonical block head](https://www.alchemy.com/overviews/proposer-builder-separation) is true\) for block 64, once the Beacon Chain receives attestations from two-thirds of the validators, block 64 is labeled as _justified \(safe\)_.  Once block 64 is labeled is justified and marked _safe,_ the previously justified block is marked as _finalized_. Because safe and _finalized_ blocks occur at the beginning of epochs, block 32 \(the first block of epoch 1\) is marked _finalized_. Here’s another way to visualize it if the current block number is 96: - Block 96 \(start of epoch 3\) = _latest_ - Block 64 \(start of epoch 2\) = _justified _\(_safe_\) - Block 32 \(start of epoch 1\) = _finalized_