Ethereum's Fusaka upgrade ships EIP-7934, enforcing a hard 10 MiB limit on the RLP-encoded size of execution blocks. This aligns execution-layer behavior with the consensus-layer's existing gossip rules, reserving 2 MiB for the beacon block header. The change prevents a class of DoS attacks that exploited the gap between gas limits and physical block size.

Previously, a malicious block could be valid under gas rules but so large it caused propagation delays or CPU exhaustion during RLP decoding. EIP-7934 fixes this by giving clients a deterministic upper bound. It ensures blocks are accepted and propagated consistently across the network, eliminating a key source of accidental forks and validator slowdowns.

This structural upgrade is a prerequisite for safely raising other throughput parameters, like the block gas limit. For developers, it means calldata-heavy rollup batches must now account for a physical 8 MiB ceiling, potentially requiring compression or chunking. The limit stabilizes the network as demand for data availability and scaling grows.