Every blob you add to a block makes it slightly harder for validators to attest to it on time. This isn't a theoretical concern — it shows up in the data today, at the current limit of 6 blobs per block. When Fulu raises that limit, the cost scales with it.
The mechanism is straightforward. The cost of getting it wrong is less obvious.
Every attestation Ethereum's 960,000-odd validators cast has a clock on it. The slot it belongs to ticks past, and then proposers have up to 32 slots to pick it up and include it in a block. Include it in the very next slot and the attester earns a full reward. Wait two slots and the head-vote component — about three-sevenths of the total attestation reward — is already gone.
Most people assume this is a solved problem. Look at the median inclusion delay and you'd agree: it sits at roughly 1.001 slots and barely moves. The typical attestation is included almost immediately.
The median isn't the story.
Every 6.4 minutes, Ethereum's consensus clients have a problem. At the boundary between epochs, they need to do expensive work — update validator balances, compute committee assignments, tick the justification/finalization machinery. While they're doing it, the network doesn't stop. Blocks keep arriving. Attesters keep committing to what they see.
What happens to validators whose client is still mid-computation when the attestation window opens? They vote for the wrong head.
One validator missing an attestation isn't a crisis. A few hundred validators missing 1 in 8 attestations, every slot, for three months straight — that's a different story. And it's concentrated in a way that the aggregate participation numbers don't show.
The xatu dataset tracks missed attestations at the entity level. When you sort by miss rate, a clear hierarchy emerges — and a handful of operators sit far outside the expected range.
When a validator is chosen to propose a block, it has a choice: publish the moment the block is ready, or wait for MEV-Boost bids to arrive and raise the payout. Most discussions frame this as a binary — you either participate in the timing game or you don't.
The data says it's more complicated. There are three distinct groups, and the middle one has mostly gone unnoticed.
Analyzing 24 hours of mainnet data: 72.5% of attestations are included in the next slot (optimal), but 27.5% are delayed. These delayed attestations earn reduced rewards.