diff --git a/AGENTS.md b/AGENTS.md
index ec7cdec..d5d1e2f 100644
--- a/AGENTS.md
+++ b/AGENTS.md
@@ -141,3 +141,10 @@ mock tool execution rather than requiring `d2` to be installed.
 Prefer structural assertions on files, metadata, registry entries, and rendered
 output manifests. Avoid brittle pixel comparisons unless a visual regression
 test is intentional and documented.
+
+## Documentation and Changelog
+
+User-facing changes — new features, behavior changes, bug fixes, breaking changes — must add an
+entry to `CHANGELOG.md` under `## [Unreleased]`, in the matching [Keep a
+Changelog](https://keepachangelog.com/en/1.1.0/) category (Added, Changed, Deprecated, Removed,
+Fixed, Security). This repository has no `docs/` yet.
diff --git a/CHANGELOG.md b/CHANGELOG.md
new file mode 100644
index 0000000..abd6554
--- /dev/null
+++ b/CHANGELOG.md
@@ -0,0 +1,37 @@
+# Changelog
+
+All notable changes to this project are documented in this file.
+
+The format follows [Keep a Changelog](https://keepachangelog.com/en/1.1.0/). This project uses
+calendar versioning (`YYYY.MM.N`) rather than semantic versioning.
+
+Add new entries under `## [Unreleased]`, in the category they belong to. At release time, rename
+`## [Unreleased]` to `## [<version>] - <YYYY-MM-DD>` and start a fresh `## [Unreleased]` above it.
+
+## [Unreleased]
+
+### Added
+
+- Allowed `hist1d` plots to have optional data (no data overlay required).
+
+## [2026.08.1] - 2026-08-19
+
+### Added
+
+- Added a D2-based graph renderer and compile hook for rendering compiled graphs as diagrams.
+- Added a schema comparison report, built on general input products.
+- Added support for Flow's variation syntax in render operations.
+- Added an area-normalisation option to comparison plots.
+
+### Changed
+
+- Moved the render model, types, and registry from `fasthep-flow` into `fasthep-render`.
+- Improved the provenance report template.
+- Render operations now skip inactive inputs instead of processing them.
+- Reorganised the internal module layout for easier navigation.
+- Renamed "author" terminology to "workflow" throughout, aligning with the published talk and
+  paper.
+
+### Fixed
+
+- D2 compile graphs now render as SVG by default, giving better text boundaries.