diff --git a/.changeset/widen-elicit-requested-schema.md b/.changeset/widen-elicit-requested-schema.md
new file mode 100644
index 000000000..c0447b082
--- /dev/null
+++ b/.changeset/widen-elicit-requested-schema.md
@@ -0,0 +1,5 @@
+---
+'@modelcontextprotocol/core': patch
+---
+
+Widen `requestedSchema` type in `ElicitRequestFormParams` to accept additional JSON Schema fields (e.g., `$schema`, `additionalProperties`) that tools like Zod's `.toJSONSchema()` produce. This removes the need for users to cast through `unknown` when passing Zod-generated schemas to `elicitInput()`.
diff --git a/packages/core/src/types/spec.types.ts b/packages/core/src/types/spec.types.ts
index f36434bef..89bacc20d 100644
--- a/packages/core/src/types/spec.types.ts
+++ b/packages/core/src/types/spec.types.ts
@@ -2795,6 +2795,7 @@ export interface ElicitRequestFormParams extends TaskAugmentedRequestParams {
      * Only top-level properties are allowed, without nesting.
      */
     requestedSchema: {
+        [key: string]: unknown;
         $schema?: string;
         type: 'object';
         properties: {
diff --git a/packages/core/src/types/types.ts b/packages/core/src/types/types.ts
index 6ac79777b..76929ab95 100644
--- a/packages/core/src/types/types.ts
+++ b/packages/core/src/types/types.ts
@@ -2024,11 +2024,13 @@ export const ElicitRequestFormParamsSchema = TaskAugmentedRequestParamsSchema.ex
      * A restricted subset of JSON Schema.
      * Only top-level properties are allowed, without nesting.
      */
-    requestedSchema: z.object({
-        type: z.literal('object'),
-        properties: z.record(z.string(), PrimitiveSchemaDefinitionSchema),
-        required: z.array(z.string()).optional()
-    })
+    requestedSchema: z
+        .object({
+            type: z.literal('object'),
+            properties: z.record(z.string(), PrimitiveSchemaDefinitionSchema),
+            required: z.array(z.string()).optional()
+        })
+        .passthrough()
 });
 
 /**