Split into sections and reorder some points.

Signed-off-by: Adam Gutglick <[email protected]>

Author: AdamGS

src/content/blog/september-2025.md

@@ -12,12 +12,27 @@ This is the second monthly issue of all that has been happening in Vortex!
 
 Development keeps moving quickly, with many new features and improvements of the Rust API. This month we accepted X commits from Y different contributors, with the relentless renovate-bot taking the crown for most changes merged.
 
-1. We merged a few big changes to the IO APIs ([#4557](https://github.com/vortex-data/vortex/pull/4608), [#4608](https://github.com/vortex-data/vortex/pull/4608)), which introduce new push-based write API (in addition to the existing stream-based one), and writes now return both the file's footer (which can now be cached, reused and even de/serialized [#4598](https://github.com/vortex-data/vortex/pull/4608)), and the file's total compressed size. Look out for a more details write-up about this block of changes, coming soon.
+## Core
+
+1. We've published an [RFC](<(https://github.com/vortex-data/vortex/pull/4726)>) presenting our planned changes to how arrays and compute interact with each other, introducing what we call Operators.
+1. We merged a few big changes to the IO APIs ([#4557](https://github.com/vortex-data/vortex/pull/4608), [#4608](https://github.com/vortex-data/vortex/pull/4608)), which introduce new push-based write API (in addition to the existing stream-based one), and writes now return both the file's footer (which can now be cached, reused and even de/serialized [#4598](https://github.com/vortex-data/vortex/pull/4608)), and the file's total compressed size.
 1. We've added a new encoding - [fastlanes](https://github.com/spiraldb/fastlanes)-based RLE [#4588](https://github.com/vortex-data/vortex/pull/4588).
-1. The work on the new FixedSizeList keeps moving forward - [#4590](https://github.com/vortex-data/vortex/pull/4590), [#4601](https://github.com/vortex-data/vortex/pull/4601)
-1. Updated our Apache DataFusion integration to the most recent release (v50.0.0) [#4577](https://github.com/vortex-data/vortex/pull/4577)
+1. The work on the new `FixedSizeList` keeps moving forward - [#4590](https://github.com/vortex-data/vortex/pull/4590), [#4601](https://github.com/vortex-data/vortex/pull/4601).
+1. We've added a new canonical encoding for list types, see the [tracking issue](https://github.com/vortex-data/vortex/issues/4699) for full details and work.
+1. We've fixed a long-standing issue where we used to underestimate the uncompressed size of arrays, causing inaccurate array stats and a consistent underestimation of the overall data size. [#4963](https://github.com/vortex-data/vortex/pull/4693).
+
+## Integrations
+
+### DuckDB
+
 1. We've both updated our DuckDB binding to support the most recent release ([1.4 - Andium](https://duckdb.org/2025/09/16/announcing-duckdb-140.html)) [#4667](https://github.com/vortex-data/vortex/pull/4667).
-1. more things...
+1. We've improved the testing of our DuckDB extension, making it easier and faster to run tests, using a debug build of DuckDB.
+
+### Apache DataFusion
+
+1. Updated our Apache DataFusion integration to the most recent release (v50.0.0) [#4577](https://github.com/vortex-data/vortex/pull/4577)
+
+## Acknowledgments
 
 We want to thank to anyone who has tried Vortex, provided feedback, asked question and filed issues.