pco/pcodec is a high-performance lossless compression library specializing in numerical sequences (integers and floats). It implements a novel three-stage pipeline: mode selection (classic, dictionary, integer/float multiplier, float quantizer), delta encoding (consecutive, lookback, conv1), and binning with tANS entropy coding. The library achieves near-Shannon-entropy compression ratios, particularly for structured numeric data like time series, columnar store blocks, and scientific datasets. It provides multiple APIs: a core Rust crate (`pco`), Python bindings via PyO3 (`pcodec` on PyPI), Java bindings via JNI (`pco-jni` on Maven Central), a C API (`pco_c`), and a feature-rich CLI for compression, decompression, inspection, and benchmarking against many other codecs (zstd, snappy, parquet, blosc, etc.). The codebase includes a legacy predecessor (`quantile-compression/q_compress`) also maintained in the same workspace. The architecture is modular, with separate crates for bit I/O (`better_io`), type dispatch macros (`dtype_dispatch`), and extensive testing including format backward compatibility and corruption recovery. It is actively developed with CI pipelines for Rust, Python, and Java.