If I'm using a ZK Rollup (like zkSync), how does the fee structure differ from an Optimistic rollup's?
The first bill (the cost of posting data back to the main chain) is fundamentally the same for both, and both benefit equally from the price reduction brought by the EIP-4844 blob mechanism. The difference mainly shows up in the second bill: beyond the execution fee, a ZK Rollup also needs to cover the computational cost of generating a cryptographic validity proof, a cost that theoretically gets reflected in the execution fee. An Optimistic Rollup, by contrast, doesn't need to generate a proof, giving it a relatively simpler execution fee structure, but it relies on the ongoing cost of running additional monitoring and fraud-proof infrastructure.
In practice, as proof-generation technology keeps improving, the marginal cost of generating a ZK Rollup's proof is dropping rapidly, and the fee gap between the two has been narrowing in recent years — not the pronounced difference seen in ZK technology's earlier days.
After EIP-4844, is Rollup fee no longer affected by main-chain congestion at all?
Not entirely. EIP-4844 made the blob data market independent from the ordinary execution fee market — meaning ordinary congestion from NFT mints or Token swaps doesn't directly push up a rollup's data-posting cost — and this has substantially reduced Rollup fees' sensitivity to everyday main-chain congestion most of the time. But blob space itself remains a limited resource; if multiple rollups simultaneously compete heavily for blob space (say, several ecosystems experiencing high-demand activity at once), the blob market itself can still get congested and drive fees up — it's just that this congestion now happens within a dedicated blob market rather than getting dragged down by the general execution fee market.
It's also worth noting that rollup fees being fully decoupled from main-chain congestion applies mainly to typical usage scenarios; if a particular application inherently requires frequent direct interaction with the main chain (certain cross-chain operations, for instance), it could still be indirectly affected by the main-chain execution fee market.
Where does the blob fee ultimately go, and what impact does this have on the Ethereum ecosystem?
Every blob base fee paid on Ethereum gets burned, meaning blob fees aren't revenue flowing to some centralized operator — they become a direct part of Ethereum's deflationary mechanism instead. As Rollup activity grows, industry estimates suggest blob fees could come to represent a fairly substantial share of ETH's total burn. This means the growth of the rollup ecosystem, to some extent, directly shows up in the Ethereum main-chain Token's supply dynamics — the economic interests of the two are, in a sense, tied together rather than two entirely separate markets.
This is also why Ethereum's core developers keep planning to expand blob capacity (gradually raising how many blobs each Block can hold) — partly to keep up with the Rollup ecosystem's growing data demand, and partly to let the blob market carry more transaction volume while contributing more real burn along the way.
As a regular user, beyond watching the fee number itself, how else can I judge whether the Rollup I've chosen is actually a good deal?
Beyond just the current fee number, a few other things are worth checking: who currently operates this rollup's Sequencer (some rollups have a single operator running the Sequencer, representing a degree of centralization risk in that part of the service), whether daily transaction volume and active user scale are large enough (reflecting whether the ecosystem is healthy and liquidity is sufficient), and this Rollup's historical pattern of fee fluctuation (some chains show notably larger execution-fee swings than others, reflecting differences in sequencer capacity planning or congestion-handling mechanisms).
If your use case involves frequent small transactions, the absolute fee number is usually the most direct consideration. But if your use case involves larger amounts or needs Finality confirmed as quickly as possible, it's more important to first confirm whether the rollup uses an Optimistic or ZK architecture and how long an actual withdrawal back to the main chain takes, rather than simply comparing fee levels.
If you complete a transaction on a Rollup like Arbitrum, Base, or Optimism, the interface usually shows just one fee number, making it feel like you paid one amount for one thing. But that seemingly single number is actually two entirely separate bills merged into one display — understanding what each bill covers and what drives it can help you figure out why fees suddenly spike, and whether there's still room for them to drop further.
For a Rollup to inherit the main chain's security, transaction data genuinely needs to be posted back to the main chain so anyone can re-verify it. Before the Dencun upgrade in March 2024 (which activated EIP-4844), rollups could only post this data as ordinary calldata on the main chain, meaning they had to compete for the same Block space as every other main-chain transaction — Token swaps, NFT mints, ordinary transfers. During peak periods, just posting a single batch of transaction data back to the main chain could cost hundreds of dollars, a cost passed directly on to end users.
EIP-4844 introduced a new data type called a blob, opening a data channel entirely separate from the ordinary fee market, dedicated to rollup use. Blob data only needs to be retained for a few weeks to let the network complete verification, rather than being stored permanently like ordinary transaction records — this dramatically lowered the cost of posting data. This single upgrade cut L2 data-posting costs by more than 90%, and it's the single biggest reason rollup fees have collapsed in recent years. The Fusaka upgrade in December 2025 further adjusted blob pricing mechanics, bringing fees more closely in line with actual computational verification costs.
The second fee is entirely independent of the first: the rollup network itself (operated by a Sequencer responsible for ordering transactions) also charges an execution fee, covering the cost of running Sequencer infrastructure and providing services like instant soft confirmations. This fee's pricing logic is typically similar to the familiar EIP-1559 mechanism on the main chain, fluctuating with that specific rollup's own real-time congestion — but its overall scale is far smaller than what data-posting costs used to represent.
This means the single fee number you see in the interface is actually the sum of "the cost of posting data back to the main chain" plus "the execution fee the rollup itself charges," and the two are driven by completely different market conditions — the data-posting cost depends on how many rollups are simultaneously competing for limited blob space at any given moment, while the execution fee depends on how congested that specific rollup's transactions happen to be at that moment.
Splitting the fee into these two bills explains a few phenomena that are easy to misread if you only look at the total number: if you notice that on the same day, Rollup A's fee suddenly spikes while Rollup B barely changes, it's likely not that something went wrong with Rollup A itself, but that other rollups were simultaneously competing heavily for blob space, driving up the overall blob market price, and A just happened to be more affected. Conversely, if a particular rollup's execution fee is unusually high, that typically indicates its sequencer is currently processing a heavy transaction volume, unrelated to the blob market.
Taking actual mid-2026 figures as an example: Base averages roughly $0.05 per transaction, Arbitrum and Optimism mainnet around $0.09, and zkSync Era around $0.07 — all far below the several-dollar-to-tens-of-dollars levels common before the Dencun upgrade. And since these chains differ in architecture and sequencer implementation, the fee differences to some extent also reflect differences in each chain's own execution fee market, not simply a matter of "which chain is cheaper."
If you regularly make small transactions on rollups, understanding that fees are made up of two separate bills can help you judge whether a fee spike is temporary market congestion (which typically subsides as congestion eases) or a longer-term pricing baseline caused by that specific rollup's own architecture. In practice, if you notice fees suddenly spiking, it's worth checking whether all rollups rose in sync (indicating overall blob market congestion) or only the specific chain you're using rose on its own (indicating congestion in that chain's own sequencer) — this can help you decide whether switching to a different rollup would actually be worthwhile, or whether simply waiting for congestion to ease is the better move.