Our earlier article on EIP-4844 blobs covered how Ethereum's Dencun upgrade in March 2024 gave rollups like Base a cheap, temporary way to publish transaction data, and how that single change cut Base's data fees by an order of magnitude almost overnight. Ethereum has since shipped a follow up upgrade called Fusaka, and it touches the same blob market again. The short version is that Fusaka made more blob space available, while also changing how a blob's minimum price is calculated. Those two changes pull in different directions, which is why this is not a simple story of fees going up or down.
What Fusaka is
Fusaka is the name of a combined Ethereum network upgrade that went live on December 3, 2025. Like Dencun before it, Fusaka is not a single change but a bundle of separate proposals (EIPs) activated together. Two pieces of that bundle matter most for anyone using Base.
More blob space, delivered gradually
Since Dencun, Ethereum has targeted a fixed number of blobs per block, and that number has been the main limit on how much cheap data capacity all rollups combined could use at once. Fusaka introduced a mechanism called Blob Parameter Only forks, or BPO forks, which let Ethereum raise that blob target without a full network upgrade each time. Public trackers report that a first such fork in December 2025 raised the per block blob target, with a second one following in January 2026 raising it again.
More blob capacity spread across the same pool of rollups generally means less competition for each block's blob slots, which is the direction that tends to push the data fee portion of a Base transaction down. This is the same dynamic our blob article described: Base is not bidding against unrelated Ethereum activity for this space, it is bidding against other rollups for a limited number of blob slots, and more slots usually means a calmer market.
A new floor under the blob price
The second change points the other way. Before Fusaka, the blob fee market could in theory sink all the way down to its minimum possible value during periods of very low demand, because the fee adjusts purely based on how full recent blocks have been. Ethereum developers considered that a flaw: at a near zero price, the market stops reflecting real demand at all, and it can also be pushed around more easily by a small amount of activity.
Fusaka added EIP-7918, which ties the minimum blob fee to the cost of ordinary Ethereum execution gas instead of letting it fall on its own. In effect, there is now a price floor under blob space that rises and falls with general Ethereum network activity, separate from how many blobs are actually being used. The practical effect is that the cheapest possible moments for blob space are not quite as cheap as they used to be, even though the market still becomes more expensive when blobs are in heavy demand, the same as before.
Why the net effect on Base fees is not settled
Put those two changes together and you get competing forces. More available blob capacity pushes the data fee down. A higher price floor pushes its minimum up. Industry commentary is split on which one wins out in practice, and figures circulating about how much blob fees have moved since Fusaka come from third party dashboards that are not fully reconciled with each other, so we are not going to repeat a specific number here as settled fact.
What we can say with more confidence is the mechanism, not the outcome: Base's L1 data fee is still a reflection of a shared, separate blob market, Fusaka changed the rules of that market in two directions at once, and the actual day to day effect is something you can observe directly rather than predict. If you want to see it for yourself, a block explorer will show you the current split between a Base transaction's execution cost and its L1 data fee, the same two components covered in our gas fees guide and our base fee and L1 data fee explainer.
What did not change
As with the Dencun upgrade, none of this touches how you actually use Base. You still connect a wallet, still see one combined fee estimate before confirming a transaction, and still do not need to pick between calldata and blobs yourself, that happens underneath the application layer. The security model is also unaffected: Base still posts data back to Ethereum and still relies on Ethereum's rules to keep that data honest, the same relationship described in our guide to how Base stays secure.
It is also worth being clear about what Fusaka is not. It is not a Base specific upgrade, and it is not related to Base's separate move toward its own unified codebase, which our OP Stack and Superchain guide covers. Fusaka is an Ethereum mainnet upgrade that every rollup sharing the blob market, Base included, inherits automatically.
The short version
Fusaka went live on Ethereum in December 2025 and reworked the blob market that Base's data fees depend on. It added a mechanism to raise blob capacity over time without a full hard fork each time, which tends to ease competition for blob space, and it added a price floor tied to Ethereum execution costs, which raises the cheapest possible price for that space. The two changes point in different directions, so rather than assume fees simply got cheaper or more expensive, the honest answer is that the mechanism changed and the net result is something worth checking on a block explorer rather than taking on faith. Nothing about how you use your wallet on Base changed because of it.
This is general information about how network fees work, not financial advice.