diff --git a/sync/advanced/compatibility.mdx b/sync/advanced/compatibility.mdx
index 0a122fea..6eb1c748 100644
--- a/sync/advanced/compatibility.mdx
+++ b/sync/advanced/compatibility.mdx
@@ -99,6 +99,7 @@ This table lists all fixes currently supported:
 | `versioned_bucket_ids`     | [Link](#versioned-bucket-ids)      | 1.15.0       | 2                |
 | `fixed_json_extract`       | [Link](#fixed-json-extract)        | 1.15.0       | 2                |
 | `custom_postgres_types`    | [Link](#custom-postgres-types).    | 1.15.3       | 2                |
+| `unstable_sqlite_expression_engine`    | [Link](#unstable_sqlite_expression_engine).    | 1.22.0       | None (unstable)           |
 
 ### `timestamps_iso8601`
 
@@ -190,3 +191,22 @@ With this fix applied:
     | 'empty';
   ```
 - Multi-ranges sync as an array of ranges.
+
+### `unstable_sqlite_expression_engine`
+
+<Danger>
+This option is experimental: When enabled, updates to the PowerSync Service might change how rows are processed
+and this option may be removed in a future version of the Service.
+</Danger>
+
+Sync Streams support scalar SQL operators (like `+`, `-` and `||`) and [functions](/sync/supported-sql#functions).
+SQL in Sync Streams should behave exactly as it would in SQLite, but the Service uses a custom implementation which differs
+from SQLite for some edge cases.
+
+To perfectly align the behavior of the Service and SQLite, enabling this option makes the Service use an actual
+SQLite database to evaluate Sync Streams.
+Some known issues with the JavaScript evaluator that are fixed by this option are:
+
+- Exact null handling: `NOT NULL` evaluates to `TRUE` without this option, enabling it yields `NULL`.
+- Without this option, `substr()` and `length()` operate on UTF-16 code units. Enabling it makes them operate on
+  Unicode code points.