💥 Breaking changes

• Remove old streaming engine (#23103)

🚀 Performance improvements

• Improve streaming groupby CSE (#23092)
• Move row index materialization in post-apply to occur after slicing (#22995)
• Add first_(true|false)_idx to BooleanChunked and use in bool arg_(min|max) (#22907)
• Don't go through row encoding for most types on index_of (#22903)
• Optimise low-level null scans and arg_max for bools (when chunked) (#22897)
• Optimize multiscan performance (#22886)

✨ Enhancements

• Native implementation for Iceberg positional deletes (#23091)
• Remove old streaming engine (#23103)
• Make match_chunks public (#23101)
• Implement StructFunction expressions in into_py (#23022)
• Basic implementation of DataTypeExpr in Rust DSL (#23049)
• Add required: bool to ParquetFieldOverwrites (#23013)
• Support serializing name.map_fields (#22997)
• Support serializing Expr::RenameAlias (#22988)
• Remove duplicate verbose logging from FetchedCredentialsCache (#22973)
• Add keys column in finish_callback (#22968)
• Add extra_columns parameter to scan_parquet (#22699)
• Add CORR function to polars SQL (#22690)
• Add per partition sort and finish callback to sinks (#22789)
• Add and test DataFrame equality functionality (#22865)
• Support descendingly-sorted values in search_sorted() (#22825)
• Derive DSL schema (#22866)

🐞 Bug fixes

• Restrict custom aggregate_function in pivot to pl.element() (#23155)
• Don't leak SourceToken in in-memory sink linearize (#23201)
• Fix panic reading empty parquet with multiple boolean columns (#23159)
• Raise ComputeError instead of panicking in truncate when mixing month/week/day/sub-daily units (#23176)
• Materialize list.eval with unknown type (#23186)
• Only set sorting flag for 1st column with PQ SortingColumns (#23184)
• Typo in AExprBuilder (#23171)
• Null return from var/std on scalar column (#23158)
• Support Datetime broadcast in list.concat (#23137)
• Ensure projection pushdown maintains right table schema (#22603)
• Don't create i128 scalars if dtype-128 is not set (#23118)
• Add Null dtype support to arg_sort_by (#23107)
• Raise error by default on invalid CSV quotes (#22876)
• Fix group_by mean and median returning all nulls for Decimal dtype (#23093)
• Fix hive partition pruning not filtering out __HIVE_DEFAULT_PARTITION__ (#23074)
• Fix AssertionError when using scan_delta() on AWS with storage_options (#23076)
• Fix deadlock on collect(background=True) / collect_concurrently() (#23075)
• Incorrect null count in rolling_min/max (#23073)
• Preserve file:// in LazyFrame node traverser (#23072)
• Respect column order in register_io_source schema (#23057)
• Incorrect output when using sort with group_by and cum_sum (#23001)
• Implement owned arithmetic for Int128 (#23055)
• Do not schema-match structs with different field counts (#23018)
• Fix confusing error message on duplicate row_index (#23043)
• Add include_nulls to Agg::Count CSE check (#23032)
• View buffer exceeding 2^32 - 1 bytes in concatenate_view (#23017)
• Fix incorrect size_hint() for FlatIter (#23010)
• Fix incorrect result selecting pl.len() from scan_csv with skip_lines (#22949)
• Allow for IO plugins with reordered columns in streaming (#22987)
• Method str.zfill was inconsistent with Python and pandas when string contained leading '+' (#22985)
• Integer underflow in propagate_nulls (#22986)
• Fix cum_min and cum_max does not preserve inf or -inf values at series start (#22896)
• Setting compat_level=0 for sink_ipc (#22960)
• Support arrow Decimal32 and Decimal64 types (#22954)
• Update arrow format (#22941)
• Fix filter pushdown to IO plugins (#22910)
• Improve numeric stability rolling_mean<f32> (#22944)
• Allow subclasses in type equality checking (#22915)
• Return early in pl.Expr.__array_ufunc__ when only single input (#22913)
• Add inline implodes in type coercion (#22885)
• Correct int_ranges to raise error on invalid inputs (#22894)
• Set the sorted flag on Array after it is sorted (#22822)
• Don't silently overflow for temporal casts (#22901)
• Fix error using write_csv with storage_options (#22881)
• Schema resolution .over(mapping_strategy="join") with non-aggregations (#22875)
• Ensure rename behaves the same as select (#22852)

📖 Documentation

• Update when_then in user guide (#23245)
• Minor improvement to cum_count docstring example (#23099)
• Add missing entry for LazyFrame __getitem__ (#22924)

📦 Build system

• Actually disable ir_serde by default (#23046)
• Add a feature flag for serde_ignored (#22957)
• Fix warnings, update DSL version and schema hash (#22953)

🛠️ Other improvements

• Update Rust Polars versions (#23229)
• Change flake to use venv (#23219)
• Add default_alloc feature to py-polars (#23202)
• Added more descriptive error message by replacing FixedSizeList with Array (#23168)
• Connect Python assert_series_equal() to Rust back-end (#23141)
• Refactor skip_batches to use AExprBuilder (#23147)
• Use ir_serde instead of serde for IRFunctionExpr (#23148)
• Separate FunctionExpr and IRFunctionExpr (#23140)
• Improve Series equality functionality and prepare for Python integration (#23136)
• Add PolarsPhysicalType and use it to dispatch into_series (#23080)
• Remove AExpr::Alias (#23070)
• Add components for Iceberg deletion file support (#23059)
• Feature gate StructFunction::JsonEncode (#23060)
• Propagate iceberg position delete information to IR (#23045)
• Add environment variable to get Parquet decoding metrics (#23052)
• Turn pl.cumulative_eval into its own AExpr (#22994)
• Add make test-streaming (#23044)
• Move scan parameter parsing for parquet to reusable function (#23019)
• Use a ref-counted UniqueId instead of usize for cache_id (#22984)
• Implement Hash and use SpecialEq for RenameAliasFn (#22989)
• Turn list.eval into an AExpr (#22911)
• Only check for unknown DSL fields if minor is higher (#22970)
• Don't enable ir_serde together with serde (#22969)
• Make dtype field on Logical non-optional (#22966)
• Add new (Frozen)Categories and CategoricalMapping (#22956)
• Add a CI check for DSL schema changes (#22898)
• Add schema parameters to expr.meta (#22906)
• Update rust toolchain in nix flake (#22905)
• Update toolchain (#22859)

Thank you to all our contributors for making this release possible!
@Athsus, @DahaoALG, @FabianWolff, @JakubValtar, @Kevin-Patyk, @MarcoGorelli, @SanjitBasker, @alexander-beedie, @borchero, @bschoenmaeckers, @cmdlineluser, @coastalwhite, @deanm0000, @dsprenkels, @eitsupi, @florian-klein, @i1oveMyse1f, @ion-elgreco, @itamarst, @kdn36, @kutal10, @math-hiyoko, @mcrumiller, @mrkn, @mroeschke, @nameexhaustion, @nikaltipar, @orlp, @paskhaver, @ritchie46, @stijnherfst, @thomasfrederikhoeck and @zyctree