Bitcoin Core merged a redesign of its optional -txindex transaction index in pull request #35531 on Aug. 15, reducing one contributor’s rebuilt mainnet database from about 66 GB to 26 GB, or roughly 61%. The saving applies only to the optional index, not Bitcoin’s blockchain or the rest of a node’s data directory. Existing indexes remain readable after an upgrade, but their larger legacy footprint remains; operators must recreate the database to realize the full reduction. The redesign uses a five-byte prefix derived from a salted SipHash and a six-byte block-and-offset suffix, then verifies the full transaction ID to prevent false matches. In the contributor’s test, lookups took about 0.2 milliseconds and a rebuild finished in 1 hour 19 minutes, compared with 1 hour 50 minutes under the old format. Stable binaries follow a separate release process, and the Bitcoin Core release index does not identify the first version containing the change. Operators will need release-specific migration notes, particularly because older releases cannot read compact-format entries and a downgrade after migration would require another rebuild.