INF V1.5 (aka S). Reworked SDKs and incremental program upgrades.
v1 solana SDKs were obstructing development so much that it was just easier to start from scratch.
Most of the docs relating to architecture and design in the old repo are still relevant and should be read prior.
$ cargo-build-sbf --version
solana-cargo-build-sbf 2.2.21
platform-tools v1.48
rustc 1.84.1