Bitcoin's Cluster Mempool: How a 15-Year Architecture Overhaul Is Rewriting the Fee Market
For fifteen years, Bitcoin's mempool — the waiting room where unconfirmed transactions sit before being mined into blocks — has operated on architecture designed when a single Bitcoin was worth pennies. That era is ending. On November 25, 2025, Bitcoin Core merged Pull Request #33629, a sweeping redesign called Cluster Mempool that replaces the legacy transaction-sorting engine with a unified, cluster-based framework. Targeted for Bitcoin Core 31.0 in the second half of 2026, this upgrade quietly ranks among the most consequential protocol-level changes Bitcoin has seen since SegWit.
No new opcodes. No token standard. No flashy narrative. Just a fundamental rethinking of how every Bitcoin node decides which transactions matter most — and why that decision has been subtly broken for years.