Bitcoin Core 32.0 Enters Release‑Candidate Phase with Faster Validation and New Fee Estimator

Bitcoin Core 32.0 entered its first release‑candidate (RC1) on Sept. 14, moving the project closer to the planned Oct. 10 final release. The update focuses on performance, fee estimation, and security without altering Bitcoin’s consensus rules.

New mempool‑aware fee estimator

The estimatesmartfee RPC now combines two methods: the traditional block‑history estimator and a new mempool‑based estimator that reflects current pending transaction conditions. When both estimators return valid values, the lower fee is returned, allowing wallets to suggest cheaper fees when the mempool is not congested. Users can select the desired estimator via the fee_rate_estimator option (block_policy, mempool_policy, or default).

Parallel block‑validation prefetching

Block validation now prefetches previous transaction outputs (prevouts) from the chainstate database using up to eight worker threads by default. The setting can be adjusted with -prevoutfetchthreads=<n>, enabling up to 16 threads or disabling the feature entirely. This change aims to reduce disk‑read latency during block processing, especially on storage with slower random‑access performance.

Security fixes

• Wallet‑notification flaw: Authenticated RPC users could craft malicious wallet names that trigger arbitrary command execution on non‑Windows nodes configured with -walletnotify. The fix treats wallet names as literal text and rejects relative‑path names containing . or ...
• HTTP server memory‑exhaustion issue: Unauthenticated REST connections could drive memory usage to ~3 GB within a minute. A patch limits request buffering, reducing memory growth to a few megabytes.

Other notable changes

• PSBT version 2 becomes the default format for four RPC commands (createpsbt, walletcreatepsbt, converttopsbt, psbtbumpfee), with an optional psbt_version argument to request older versions.
• New RPCs exportwatchonlywallet and derivehdkey enhance watch‑only wallet handling and hierarchical deterministic key derivation.
• AssumeUTXO background validation progress is now reported via getblockchaininfo.

Developers opened a dedicated testing feedback issue on Sept. 15 and encourage node operators and wallet developers to run the RC and report problems through GitHub. Bitcoin Core does not auto‑update; operators must manually install new binaries.