This EIP introduces Blob Parameter Only (BPO) Hardforks, a lightweight mechanism for incrementally scaling Ethereum’s blob capacity through targeted hard forks that modify only blob-related parameters: target, max, and baseFeeUpdateFraction. Unlike traditional hard forks, which require extensive coordination and introduce broader protocol changes, BPO forks enable rapid, low-overhead scaling of blob capacity in response to real-world demand and network conditions.
Ethereum's scaling strategy relies on Layer 2 (L2) solutions for transaction execution while using Ethereum as a data availability (DA) layer. However, the demand for DA has increased rapidly, and the current approach of only modifying blob parameters in large, infrequent hard forks is not agile enough to keep up with L2 growth.
The key motivations for BPO forks are as follows:
Continuous Scaling
Reduced Operational Overhead
Enhanced Stability with New Scaling Technologies
Predictable Upgrades for Builders
BPO hardforks are defined as protocol upgrades that modify only blob-related parameters through configuration, without requiring any client-side code changes. The new parameters take effect immediately at the specified activation time.
The following protocol parameters are now managed by the blob schedule configuration:
target): The expected number of blobs per block.max): The maximum number of blobs per block.baseFeeUpdateFraction): Determines how blob gas pricing adjusts per block.To ensure consistency, when a regular hardfork changes any of these parameters, it MUST do so by adding an entry to the blob schedule configuration.
To facilitate these changes on the execution layer, each fork in the blobSchedule object defined in EIP-7840 is linked to an activation timestamp via a top-level <fork_name>Time field, which holds the Unix timestamp of the activation slot as a JSON number. BPO forks SHOULD be named using the convention bpo<index>, where <index> starts at 1. Left padding is unnecessary since these labels are not subject to lexicographic sorting. Activation timestamps are required only for forks that occur after Prague.
Since there is no backporting, the values for cancunTime and pragueTime are set to 0. It should also be noted that the other parameters and schedules above are purely illustrative. Actual values and schedules are beyond the scope of this specification.
We modify the functions get_base_fee_per_blob_gas and calc_excess_blob_gas defined in EIP-4844 to explicitly use the blob schedule.
In line with how updating BLOB_BASE_FEE_UPDATE_FRACTION was handled in EIP-7691, the functions use the current block's blob schedule.
Moreover, TARGET_BLOB_GAS_PER_BLOCK is removed and replaced with GAS_PER_BLOB * blob_schedule.target, as it is now redundant.
A new BLOB_SCHEDULE field is added to consensus layer configuration, containing a sequence of entries representing blob parameter changes after ELECTRA_FORK_EPOCH. There exists one entry per fork that changes blob parameters, whether it is a regular or a Blob-Parameter-Only fork.
The parameters and schedules above are purely illustrative. Actual values and schedules are beyond the scope of this specification.
Requirements:
blobSchedule MUST align with the start of the epoch specified in the consensus layer configuration.max field in the EL's blobSchedule MUST equal the MAX_BLOBS_PER_BLOCK value in the consensus layer configuration.compute_fork_digestThe compute_fork_digest helper is updated to account for BPO forks:
In the consensus layer, ENRs are extended with an additional entry nfd, short for "next fork digest". This field communicates the digest of the next scheduled fork, regardless of whether it is a regular or BPO fork. This approach is preferred over encoding BPO-specific parameters because it is agnostic to specific use cases and offers greater long-term flexibility.
| Key | Value |
|---|---|
nfd | SSZ Bytes4 ForkDigest |
When discovering and interfacing with peers, nodes MUST evaluate nfd alongside their existing consideration of the ENRForkID::next_* fields under the eth2 key, to form a more accurate view of the peer's intended next fork.
Status req/respNo changes are needed in this interaction, but it is noted that the response payload must correctly contain the updated fork_digest.
No changes are required to topic structure or configuration. However, all topics will automatically rotate at a BPO fork due to changes in their ForkDigestValue component.
Full hard forks require extensive coordination, testing, and implementation changes beyond parameter adjustments. For example, in Lighthouse, a typical hard fork implementation requires thousands of lines of boilerplate before any protocol changes occur. BPO forks streamline this process by avoiding the need for this boilerplate code.
Allowing blob parameters to be configured externally enables rapid experimentation, testing, and adjustments without requiring code changes across client implementations. Testing teams can investigate different parameters with minimal involvement from client implementers.
BPO forks introduce no backwards compatibility concerns.
No security risks have been identified.
Copyright and related rights waived via CC0.