Bitcoin Optech newsletter #409 is here:

- describes a draft BIP to replace the testnet4 test network with a successor
- Optech Newsletter #409 Podcast
https://bitcoinops.org/en/newsletters/2026/06/12/

Pol Espinasa posted to the Bitcoin-Dev mailing list a draft BIP, co-authored with Fabian Jahr, to replace testnet4 with testnet5...
https://bitcoinops.org/en/newsletters/2026/06/12/#draft-bip-for-testnet5

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