diff --git a/fern/snippets/openapi-specs.mdx b/fern/snippets/openapi-specs.mdx
index ac63bedc4..bd590341a 100644
--- a/fern/snippets/openapi-specs.mdx
+++ b/fern/snippets/openapi-specs.mdx
@@ -149,6 +149,12 @@ api:
   If true, preserve oneOf structures with a single schema. If false, unwrap them.
 </ParamField>
 
+<ParamField path="settings.preserve-one-of-in-all-of" type="boolean" default="false" toc={true}>
+  Whether to keep a `oneOf` or `anyOf` that appears as a member of an `allOf` as a union. When `false`, every variant's properties are merged into a single object and marked optional, which makes invalid property combinations representable. When `true`, the `allOf` is distributed over the union: `allOf: [oneOf: [A, B, C], S]` becomes `oneOf: [A & S, B & S, C & S]`, an undiscriminated union in which each variant keeps its own required properties alongside the shared ones.
+
+  Enabling this setting changes the generated request and response shapes for affected schemas in every SDK, and the API Reference renders a variant selector for them. Union members that declare a `discriminator` are left intact.
+</ParamField>
+
 <ParamField path="settings.filter" type="object" toc={true}>
   Filter to apply to the OpenAPI specification. Use this to limit which endpoints are included in the generated SDK or API Reference docs [based on their paths](/learn/api-definitions/openapi/extensions/audiences#path-based-filtering).