Engineering
Notes from the engine room.
How we build the systems under 21st Care — rebuilding the software that runs healthcare finance as small, fast, provably faithful engines.
- 17 min read
Engineering the fastest FHIR server
Read the postOur FHIR R4 server is a Rust engine over two databases: Postgres owns the patient graph and ClickHouse owns the observation time series. Byte-serving reads, parse-once ingest, and one typed query AST make it fast; committed benchmarks and a config-flip equivalence harness keep it honest.
- 9 min read
Rebuilding the MS-DRG grouper in Rust
Read the postThe MS-DRG grouper decides what every Medicare inpatient stay pays. We rebuilt it as a pure Rust library — parsing the official grouper’s own data byte-for-byte, compiling its embedded formula language, and holding every answer to differential tests against the reference implementation.