Polars releases 2.0 release candidate with streaming default

Polars has released the first release candidate for version 2.0, changing LazyFrame query collection to use its streaming engine by default. The project says the change should improve memory use and performance on most queries, with an aggregate expectation that the engine will be five times faster. The new default does not guarantee row order for operations including joins, group-bys and unpivots; users can request ordering or retain the in-memory engine. The release candidate also adds stricter behavior for type mismatches and horizontal concatenation, turning some previously silent outcomes into errors.