Polars vs Fulcrum

Polars publishes two trains into one feed: Python releases roughly weekly through 1.42.0 to 1.43.2, and Rust releases on their own numbering, with 0.54.4 carrying the milestone that the streaming engine is stabilized. The dominant thread across the Python releases is deprecation — casts from string to temporal types, numeric-to-categorical and categorical-to-integer casts, casts from non-nested dtypes into lists, bitwise ops between integers and booleans, cat.get_categories(), cat.to_local(), LazyFrame.profile(), and to_struct() calls without field names. Alongside it, cloud IO keeps getting attention: bytes-based concurrency control, callback sinks on cloud, and non-blocking path expansion.

A deprecation batch this size is not routine tidying — it is the removal list for a future major, and the common theme is closing implicit conversions that silently change semantics. The performance and correctness work points the same way, toward the streaming engine as the default execution path rather than a mode: nested common subplan elimination, streaming grouped AsOf joins, hand-written Thrift for parquet metadata decode, and repeated fixes to sortedness and chunking on the streaming path. Cloud is the third leg, with the engine being taught to run against object storage without materializing.

With the streaming engine marked stable and this many APIs deprecated in a single wave, the deprecations are the visible countdown to a release that removes them. The entries do not say when, so the safer read is that the next Python releases keep pairing streaming-path fixes with further deprecation notices rather than breaking anything yet.