tl;dr: Polars 2.0 (release candidate out now) makes the streaming engine the default for LazyFrame queries, promising ~5x performance gains and lower memory usage, though row-order is no longer guaranteed for operations like joins and group_by without opting in via `maintain_order=True`. The release also enforces stricter behavior—rejecting lossy type coercions in `is_in`, requiring matching heights in horizontal concat, and removing ambiguous casts in favor of dedicated parsing methods. Removed APIs now raise informative typed exceptions pointing to replacements, and upcoming 2.x work includes out-of-core streaming, a cost-based planner, and a new S3 reader.