Utreexo IBD, unspendable taproot internal keys - Bitcoin Optech Newsletter #423

Bitcoin Optech newsletter #423 is here:

• summarizes an analysis of mining pool difficulty controllers stranding slowed miners
• describes a proposed improvement to Utreexo’s initial block download
• links to a draft BIP for specifying unspendable taproot internal keys
• summarizes changes to services/client software
• Optech Newsletter #423 Podcast https://bitcoinops.org/en/newsletters/2026/09/18/

Eric Price posted to Delving Bitcoin an analysis of how mining pools adjust difficulty for a miner that slows down.. https://bitcoinops.org/en/newsletters/2026/09/18/#vardiff-controllers-that-strand-slowing-miners

Davidson Souza posted to Delving Bitcoin about a way to improve the performance of Utreexo during initial block download (IBD)... https://bitcoinops.org/en/newsletters/2026/09/18/#improvements-in-utreexo-initial-block-download

NTL posted to the Bitcoin-Dev mailing list about his proposal for a new BIP draft to specify how to make the taproot key path unspendable... https://bitcoinops.org/en/newsletters/2026/09/18/#new-bip-draft-for-unspendable-internal-keys

Changes to services and client software:

• BitBoxApp adds Spark-based Lightning payments
• Covenants.diy script editor
• EntropyLab offline key calculator https://bitcoinops.org/en/newsletters/2026/09/18/#changes-to-services-and-client-software

Bitcoin Optech will host an audio recap discussion of this newsletter streaming live on X/Twitter Tuesday at 16:30 UTC.