diff --git a/fern/providers/observability/langfuse.mdx b/fern/providers/observability/langfuse.mdx
index 986832db9..d3b782dff 100644
--- a/fern/providers/observability/langfuse.mdx
+++ b/fern/providers/observability/langfuse.mdx
@@ -77,6 +77,23 @@ To make the most out of this integration, you can now use Langfuse's [evaluation
 </Step>
 </Steps>
 
+## Server Version Detection and SDK Routing
+
+When you save a Langfuse credential, Vapi probes your server's `/api/public/health` endpoint and automatically resolves the Langfuse server version. The credential stores this resolved version, and Vapi uses it to pick the export path for your traces:
+
+- **Langfuse Cloud and self-hosted servers on version 3.63 or later** receive traces through the Langfuse JS SDK v5 OTLP export path.
+- **Self-hosted servers on versions earlier than 3.63** continue to receive traces through the legacy v3 ingestion API.
+
+You do not need to configure anything; routing follows the resolved server version. All Langfuse Cloud regions (`us.cloud.langfuse.com`, `hipaa.cloud.langfuse.com`, `jp.cloud.langfuse.com`, and `cloud.langfuse.com`) are fully supported, and self-hosted Langfuse v3 remains supported through the upstream v3 patch window ending January 31, 2027.
+
+If Vapi cannot reach your server when you save the credential, you can enter the server version manually. The next successful probe corrects the stored version automatically.
+
+## Troubleshooting
+
+**Host URL is refused when saving.** Host URLs that redirect to a different origin are rejected because trace exports do not follow redirects. For example, `https://eu.cloud.langfuse.com` redirects to `https://cloud.langfuse.com`, so use `https://cloud.langfuse.com` directly. The error message names the URL to use.
+
+**Traces stop appearing during calls.** If tracing fails during a call, for example because your server became unreachable or was upgraded or downgraded across the v3/v5 boundary, Vapi emits a call log error linking to the [credentials page](https://dashboard.vapi.ai/keys). Re-save your Langfuse credential there so Vapi can re-resolve the server version.
+
 ## Enrich Traces
 Vapi allows you to enrich Langfuse traces by integrating [Metadata](https://langfuse.com/docs/tracing-features/metadata) and [Tags](https://langfuse.com/docs/tracing-features/tags).