diff --git a/packages/openapi-generator/src/openapi.ts b/packages/openapi-generator/src/openapi.ts
index 87f236e9..2350221d 100644
--- a/packages/openapi-generator/src/openapi.ts
+++ b/packages/openapi-generator/src/openapi.ts
@@ -126,6 +126,26 @@ function routeToOpenAPI(route: Route): [string, string, OpenAPIV3.OperationObjec
   const isUnstable = jsdoc.tags?.unstable !== undefined;
   const example = jsdoc.tags?.example;
 
+  const knownTags = new Set([
+    'operationId',
+    'summary',
+    'private',
+    'unstable',
+    'example',
+    'tag',
+    'description',
+    'url',
+  ]);
+  const unknownTagsObject = Object.entries(jsdoc.tags ?? {}).reduce(
+    (acc, [key, value]) => {
+      if (!knownTags.has(key)) {
+        return { ...acc, [key]: value || true };
+      }
+      return acc;
+    },
+    {},
+  );
+
   const requestBody =
     route.body === undefined
       ? {}
@@ -147,6 +167,9 @@ function routeToOpenAPI(route: Route): [string, string, OpenAPIV3.OperationObjec
       ...(tag !== '' ? { tags: [tag] } : {}),
       ...(isInternal ? { 'x-internal': true } : {}),
       ...(isUnstable ? { 'x-unstable': true } : {}),
+      ...(Object.keys(unknownTagsObject).length > 0
+        ? { 'x-unknown-tags': unknownTagsObject }
+        : {}),
       parameters: route.parameters.map((p) => {
         // Array types not allowed here
         const schema = schemaToOpenAPI(p.schema);
diff --git a/packages/openapi-generator/test/openapi.test.ts b/packages/openapi-generator/test/openapi.test.ts
index 150d4afc..d8c179fa 100644
--- a/packages/openapi-generator/test/openapi.test.ts
+++ b/packages/openapi-generator/test/openapi.test.ts
@@ -16,7 +16,11 @@ import {
 async function testCase(
   description: string,
   src: string,
-  expected: OpenAPIV3_1.Document<{ 'x-internal'?: boolean; 'x-unstable'?: boolean }>,
+  expected: OpenAPIV3_1.Document<{
+    'x-internal'?: boolean;
+    'x-unstable'?: boolean;
+    'x-unknown-tags'?: object;
+  }>,
   expectedErrors: string[] = [],
 ) {
   test(description, async () => {
@@ -1192,3 +1196,135 @@ testCase(
     },
   },
 );
+
+const ROUTE_WITH_UNKNOWN_TAG = `
+import * as t from 'io-ts';
+import * as h from '@api-ts/io-ts-http';
+
+/**
+ * A simple route
+ *
+ * @operationId api.v1.test
+ * @tag Test Routes
+ * @optout true
+ */
+export const route = h.httpRoute({
+  path: '/foo',
+  method: 'GET',
+  request: h.httpRequest({}),
+  response: {
+    200: {
+      test: t.string
+    }
+  },
+});
+`;
+
+testCase('route with unknown tag', ROUTE_WITH_UNKNOWN_TAG, {
+  openapi: '3.0.3',
+  info: {
+    title: 'Test',
+    version: '1.0.0',
+  },
+  paths: {
+    '/foo': {
+      get: {
+        summary: 'A simple route',
+        operationId: 'api.v1.test',
+        tags: ['Test Routes'],
+        'x-unknown-tags': {
+          optout: 'true',
+        },
+        parameters: [],
+        responses: {
+          200: {
+            description: 'OK',
+            content: {
+              'application/json': {
+                schema: {
+                  type: 'object',
+                  properties: {
+                    test: {
+                      type: 'string',
+                    },
+                  },
+                  required: ['test'],
+                },
+              },
+            },
+          },
+        },
+      },
+    },
+  },
+  components: {
+    schemas: {},
+  },
+});
+
+const ROUTE_WITH_MULTIPLE_UNKNOWN_TAGS = `
+import * as t from 'io-ts';
+import * as h from '@api-ts/io-ts-http';
+
+/**
+ * A simple route
+ *
+ * @operationId api.v1.test
+ * @tag Test Routes
+ * @optout true
+ * @critical false
+ */
+export const route = h.httpRoute({
+  path: '/foo',
+  method: 'GET',
+  request: h.httpRequest({}),
+  response: {
+    200: {
+      test: t.string
+    }
+  },
+});
+`;
+
+testCase('route with multiple unknown tags', ROUTE_WITH_MULTIPLE_UNKNOWN_TAGS, {
+  openapi: '3.0.3',
+  info: {
+    title: 'Test',
+    version: '1.0.0',
+  },
+  paths: {
+    '/foo': {
+      get: {
+        summary: 'A simple route',
+        operationId: 'api.v1.test',
+        tags: ['Test Routes'],
+        'x-unknown-tags': {
+          optout: 'true',
+          critical: 'false',
+        },
+        parameters: [],
+        responses: {
+          200: {
+            description: 'OK',
+            content: {
+              'application/json': {
+                schema: {
+                  type: 'object',
+                  properties: {
+                    test: {
+                      type: 'string',
+                    },
+                  },
+                  required: ['test'],
+                },
+              },
+            },
+          },
+        },
+      },
+    },
+  },
+  components: {
+    schemas: {},
+  },
+});