🚀 Performance improvements

• Fix cross join batch size when one of the DataFrames is tiny (#14347)
• Fix binview growable complexity O(n*m) -> O(n) (#15628)
• Remove extra thread spawn from row group fetcher (#15626)
• Use vertical parallelism if input is chunked for Filter,Select,WithColumns (#15608)
• Refactor CSV serialization to not go thorough AnyValue (#15576)
• don't use dynamic dispatch in visitors (#15607)
• Improve Bitmap construction performance (#15570)
• join by row-encoding (#15559)

✨ Enhancements

• add Expr.dt.add_business_days and Series.dt.add_business_days (#15595)
• Add str.head and str.tail (#14425)
• Add union/or operator for pl.Enum (#14965)
• Extended BytecodeParser to handle additional math functions, and imports from the global namespace (#15627)
• Push down is_between expressions to Arrow (#15180)
• add holidays argument to business_day_count (#15580)
• change default to write parquet statistics (#15597)
• Expressify to_integer (#15604)
• Optimizer; remove double SORT and redundant projections (#15573)
• Add null_on_oob parameter to expr.array.get (#15426)
• support weekend argument in business_day_count (#15544)
• Enable is_first/last_distinct for not nested non-numeric list (#15552)
• Turn off cse if cache node found (#15554)
• Tag concat list as elementwise (#15545)

🐞 Bug fixes

• Return appropriate data type for time mean and median (#14471)
• Fix issue in write_excel that could lead to incorrect spanning range determination (#15631)
• Output correct dtype for mean_horizontal on a single column (#15118)
• Recompute RowIndex schema after projection pd (#15625)
• Mean of boolean in streaming group_by incorrectly always gave NULL (#15616)
• Include cloud creds in cache key (#15609)
• Fix elementwise-apply if any input is AggregatedScalar (#15606)
• Explode list should take validity into account (#15572)
• use larger recursive stack in debug mode (#15593)
• SQL interface "off-by-one' indexing error with GROUP BY clauses that use position ordinals (#15584)
• Enable missing features in polars-time (#15558)
• Handle quoted identifiers when registering CTEs in the SQL engine (#15564)
• Decompress moved out of schema initialization (#15550)
• Turn off cse if cache node found (#15554)

📖 Documentation

• Add legacy CPU install instructions in user guide (#13676)
• Examples for errors (#13724)
• Add docstring examples for reading json (#14481)
• Add security warning in LazyFrame.deserialize() docstring (#15282)
• Various minor updates to User Guide's SQL intro section (#15557)

🛠️ Other improvements

• Replace most deprecated calls with bounded version (#15632)
• use bound api (#15630)
• Initial PyO3 0.21 support (#15622)
• Don't run streaming group-by in partitionable gb (#15611)
• pref(rust!, python): Unify sort with SortOptions and SortMultipleOptions (#15590)
• Set up CodSpeed (#15537)

Thank you to all our contributors for making this release possible! @CanglongCl, @ChayimFriedman2, @Fokko, @JamesCE2001, @MarcoGorelli, @NedJWestern, @TrevorWinstral, @alexander-beedie, @deanm0000, @douglas-raillard-arm, @eitsupi, @filabrazilska, @i-aki-y, @itamarst, @leoforney, @mcrumiller, @nameexhaustion, @orlp, @ozgrakkurt, @reswqa, @ritchie46 and @stinodego