Fix Anthropic 'Invalid signature in thinking block' 400 Error in n8n AI Agent (GH #41152)

Description and use

<p>Your support-ticket agent runs fine all morning, then randomly throws <code>Bad request - please check your parameters</code> on the AI Agent node. No credentials expired, nothing changed in the workflow, and re-running the same prompt sometimes works. Underneath that generic message, Anthropic returned a very specific 400:<br> </p> <div class="highlight js-code-highlight"> <pre class="highlight json"><code><span class="mi">400</span><span class="w"> </span><span class="p">{</span><span class="nl">"type"</span><span class="p">:</span><span class="s2">"error"</span><span class="p">,</span><s

Problem

<p>Your support-ticket agent runs fine all morning, then randomly throws <code>Bad request - please check your parameters</code> on the AI Agent node. No credentials expired, nothing changed in the workflow, and re-running the same prompt sometimes works. Underneath that generic message, Anthropic returned a very specific 400:<br> </p> <div class="highlight js-code-highlight"> <pre class="highlight json"><code><span class="mi">400</span><span class="w"> </span><span class="p">{</span><span class="nl">"type"</span><span class="p">:</span><span class="s2">"error"</span><span class="p">,</span><s

Outcome

<p>Your support-ticket agent runs fine all morning, then randomly throws <code>Bad request - please check your parameters</code> on the AI Agent node. No credentials expired, nothing changed in the workflow, and re-running the same prompt sometimes works. Underneath that generic message, Anthropic returned a very specific 400:<br> </p> <div class="highlight js-code-highlight"> <pre class="highlight json"><code><span class="mi">400</span><span class="w"> </span><span class="p">{</span><span class="nl">"type"</span><span class="p">:</span><span class="s2">"error"</span><span class="p">,</span><s

Evidence

Fix Anthropic 'Invalid signature in thinking block' 400 Error in n8n AI Agent (GH #41152)

Source