Binary Fuse filters as an alternative to BIP 158 GCS

At the recent Chaincode BOSS 2026 event, a new exploration into set-membership algorithms for light clients in Bitcoin was initiated, focusing on whether Binary Fuse filters could serve as a superior alternative to the currently employed Golomb-Coded Sets (GCS) as specified in BIP158. This inquiry was prompted by the introduction of Binary Fuse filters after the drafting of BIP158, coupled with a hypothesis that they might present a more efficient CPU and bandwidth balance.

A comprehensive benchmarking framework has been established utilizing Bitcoin Core’s infrastructure to assess these alternatives across approximately 50,000 mainnet blocks. The tests spanned various wallet sizes on both x86 systems and ARM-based systems like the Raspberry Pi 5, with a rigorous validation against ground truth to ensure accuracy. The research, along with detailed methodologies and code, is accessible at Light Client Block Filter Research (Binary Fuse Filters).

Preliminary results indicate that the 16-bit Binary Fuse filter variant, termed Fuse16, drastically reduces CPU usage—between approximately 9 to 80 times on desktop systems and 6 to 45 times on ARM systems—with only a minimal increase in bandwidth consumption (around 0–3%). This positions Fuse16 as an effective direct replacement for GCS, without significant trade-offs in network performance.

Despite these promising outcomes, several questions have been raised about the broader implications of adopting Binary Fuse filters. These include evaluating the acceptability of minor bandwidth increases in exchange for substantial CPU efficiency gains, potential overlooked complexities or vulnerabilities associated with Binary Fuse filters, and whether the increase in complexity and potential for privacy leaks with proposed hierarchical constructions are justifiable risks.

Additionally, there's consideration for further development of the benchmarking framework to enhance its modularity and usability for others in the community who may wish to test different algorithms against BIP158 using real mainnet data. While the current framework meets the needs of this initial research, its expansion could facilitate broader comparative studies and contributions from other developers.

This project marks a significant personal milestone as it represents the first open-source and Bitcoin-related publication by the researcher, who has primarily worked within corporate environments. Feedback from the wider Bitcoin and cryptographic community is sought to refine and advance this exploratory work.