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

The documents specify cross-input signature aggregation for a new Taproot output type, but they remain drafts, and the soft fork they require has no activation plan and no wallet support.

- Published: 2026-11-11T05:35:20.767Z
- Canonical: https://polylog.news/crypto/2026-11-11/bitcoin-developers-merge-three-signature-aggregation-proposa
- Publisher: Polylog (Crypto desk)
- Section: crypto
- Sources: [CryptoSlate](https://cryptoslate.com/bitcoin-devs-merge-3-new-bips-and-transaction-fees-could-plummet/), [bips.dev](https://bips.dev/), [GitHub bitcoin/bips](https://github.com/bitcoin/bips), [bitcoin++ Insider](https://insider.btcpp.dev/p/cisa-in-60-seconds-fabian-jahr-toronto), [Spark glossary](https://www.spark.money/glossary/cross-input-signature-aggregation), [Human Rights Foundation](https://hrf.org/wp-content/uploads/2025/03/CISA-Industry-Paper-V4.pdf), [crypto.news](https://crypto.news/bitcoin-public-key-exposure-quantum-risk/)

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](https://cryptoslate.com/bitcoin-devs-merge-3-new-bips-and-transaction-fees-could-plummet/). 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](https://bips.dev/) 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](https://github.com/bitcoin/bips) 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](https://www.spark.money/glossary/cross-input-signature-aggregation) [technical summaries](https://insider.btcpp.dev/p/cisa-in-60-seconds-fabian-jahr-toronto). 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](https://hrf.org/wp-content/uploads/2025/03/CISA-Industry-Paper-V4.pdf) 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](https://crypto.news/bitcoin-public-key-exposure-quantum-risk/) sits in outputs whose public keys are already visible.

## What this means

The channel is block-space cost per input. If CISA activates, high-input users such as exchanges, custodians, Lightning channel operators and CoinJoin coordinators pay less, and miners collect less fee revenue per transaction. That matters more each halving because miners depend more on fees as the subsidy shrinks. The market treats Bitcoin's base protocol as effectively frozen, so none of this is priced. The view that Bitcoin cannot upgrade is still mostly right on timing. Taproot's specifications were published in early 2020 and activated in November 2021, and wallet adoption came slowly after that. The likelier outcome is that CISA stays a specification for at least a year. Its near-term effect is a sharper argument over which soft fork deserves the next activation slot, signature efficiency or quantum resistance. Rising estimates of quantum-exposed supply favor quantum resistance. The forward read would be wrong if Bitcoin Core merges BIP 460 consensus code with activation parameters within the next year.

## What to watch

- Whether Bitcoin Core reviewers move the BIP 460 reference implementation out of draft status, because no activation can happen without merged, reviewed consensus code.
- Whether major wallet and custody providers publicly commit to building full-aggregation signing, which requires signers to interact and is the main practical barrier to the larger fee savings.
- Whether developers who prioritize quantum resistance argue against spending a soft fork on a Schnorr-based scheme, which would show how the developer community ranks the two problems.