Bitcoin Developers Merge Three Signature-Aggregation Proposals That Could Cut Fees by Up to 27%

Bitcoin developers have merged three Bitcoin Improvement Proposals (BIPs) into the project's proposal repository. Together they specify cross-input signature aggregation (CISA), CryptoSlate reported. This is the most concrete step so far toward a proposal that developers have discussed for years without a full specification.

The repository index lists the three documents by number. BIP 458 covers half-aggregation of BIP 340 Schnorr signatures. BIP 459 covers full aggregation using a scheme called DahLIAS. BIP 460 applies CISA to Taproot key-path spends in a new SegWit version 2 output type. The repository listing shows the documents with status Draft, with developer Fabian Jahr named as the author of 459 and 460. A merge places a text in the official record. It does not change the rules any node enforces.

Today every transaction input carries its own 64-byte signature. Full aggregation lets the signers of a transaction produce one 64-byte signature for all inputs, but the signers must interact to create it. Half-aggregation needs no interaction and cuts signature data roughly in half, according to technical summaries. CryptoSlate's modeling estimates that full aggregation would lower fees by about 14% for a joint payment and about 27% for a consolidation transaction. It also notes that activation and wallet support remain unresolved.

The saving grows with the number of inputs in a transaction, so the largest benefit goes to transactions that combine many inputs. That includes exchange and custodian consolidation, and also collaborative transactions in which several users merge their inputs to break the on-chain link between sender and receiver (CoinJoin). A 2025 industry paper by Jahr presents this as a way to make privacy-preserving transactions cheaper than solo ones.

BIP 460 needs a soft fork because it defines a new output type. It also builds on elliptic-curve Schnorr signatures, which a sufficiently large quantum computer could break. That puts it in competition for developer attention with post-quantum work at a time when Glassnode says 35.4% of issued bitcoin sits in outputs whose public keys are already visible.