diff --git a/docs/guide/custom.ipynb b/docs/guide/custom.ipynb
index 3ad105d..78e7b9c 100644
--- a/docs/guide/custom.ipynb
+++ b/docs/guide/custom.ipynb
@@ -416,6 +416,7 @@
     "\n",
     "input_string = \"\"\"{\n",
     "    \"type\": \"identity\",\n",
+    "    \"spec_version\": \"2.1\",\n",
     "    \"id\": \"identity--311b2d2d-f010-4473-83ec-1edf84858f4c\",\n",
     "    \"created\": \"2015-12-21T19:59:11Z\",\n",
     "    \"modified\": \"2015-12-21T19:59:11Z\",\n",
@@ -512,6 +513,7 @@
        ".highlight .vm { color: #19177C } /* Name.Variable.Magic */\n",
        ".highlight .il { color: #666666 } /* Literal.Number.Integer.Long */</style><div class=\"highlight\"><pre><span></span><span class=\"p\">{</span>\n",
        "    <span class=\"nt\">&quot;type&quot;</span><span class=\"p\">:</span> <span class=\"s2\">&quot;identity&quot;</span><span class=\"p\">,</span>\n",
+       "    <span class=\"nt\">&quot;spec_version&quot;</span><span class=\"p\">:</span> <span class=\"s2\">&quot;2.1&quot;</span><span class=\"p\">,</span>\n",
        "    <span class=\"nt\">&quot;id&quot;</span><span class=\"p\">:</span> <span class=\"s2\">&quot;identity--311b2d2d-f010-4473-83ec-1edf84858f4c&quot;</span><span class=\"p\">,</span>\n",
        "    <span class=\"nt\">&quot;created&quot;</span><span class=\"p\">:</span> <span class=\"s2\">&quot;2015-12-21T19:59:11.000Z&quot;</span><span class=\"p\">,</span>\n",
        "    <span class=\"nt\">&quot;modified&quot;</span><span class=\"p\">:</span> <span class=\"s2\">&quot;2020-06-24T18:29:24.099Z&quot;</span><span class=\"p\">,</span>\n",