diff --git a/CHANGELOG.md b/CHANGELOG.md
index 67672f2d0..ecd70d732 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -2,6 +2,24 @@
 
 ## [10.0.0](https://github.com/mermaid-js/mermaid/releases/tag/v10.0.0)
 
+
+### Mermaid is ESM only!
+
+We've dropped CJS support. So, you will have to update your import scripts as follows.
+
+```html
+<script type="module">
+  import mermaid from 'https://cdn.jsdelivr.net/npm/mermaid@10/dist/mermaid.esm.min.mjs';
+  mermaid.initialize({ startOnLoad: true });
+</script>
+```
+
+You can keep using v9 by adding the `@9` in the CDN URL.
+```diff
+- <script src="https://cdn.jsdelivr.net/npm/mermaid/dist/mermaid.js"></script>
++ <script src="https://cdn.jsdelivr.net/npm/mermaid@9/dist/mermaid.js"></script>
+```
+
 ### mermaid.render is async and doesn't accept callbacks
 
 ```js