feat: document Langfuse traceName field for custom trace naming

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: Vapi Tasker

fern/apis/api/openapi.json

@@ -10172,6 +10172,10 @@
           "metadata": {
             "type": "object",
             "description": "This is a JSON object that will be added to the Langfuse trace. Traces can be enriched with metadata to better understand your users, application, and experiments. https://langfuse.com/docs/tracing-features/metadata\nBy default it includes the call metadata, assistant metadata, and assistant overrides."
+          },
+          "traceName": {
+            "type": "string",
+            "description": "Custom name for the Langfuse trace. Supports Liquid templates with the following variables: {{ call.id }} (call UUID), {{ call.type }} (inboundPhoneCall, outboundPhoneCall, webCall), {{ assistant.name }} (assistant display name), {{ assistant.id }} (assistant UUID). Example: '{{ assistant.name }} - {{ call.type }}'. Defaults to the call ID if not provided or if template rendering fails."
           }
         },
         "required": [

fern/changelog/2026-02-11.mdx

@@ -0,0 +1 @@
+1. **Custom Trace Names for Langfuse**: You can now customize Langfuse trace names using the new `traceName` field in [`LangfuseObservabilityPlan`](https://api.vapi.ai/api#:~:text=LangfuseObservabilityPlan). Instead of raw call IDs, use [Liquid templates](https://shopify.github.io/liquid/) with variables like `{{ assistant.name }}` and `{{ call.type }}` to create descriptive, filterable trace names. If `traceName` is not set or a template error occurs, traces fall back to the call ID. See the [Langfuse integration guide](/providers/observability/langfuse) for details.

fern/providers/observability/langfuse.mdx

@@ -112,3 +112,59 @@ Adding metadata and tags makes it easier to filter, analyze, and monitor your as
 
 ### Example
 ![Langfuse Metadata Example](../../static/images/providers/langfuse-example.png)
+
+## Custom Trace Names
+
+By default, Langfuse traces are named using the raw call ID. You can customize trace names using the [`assistant.observabilityPlan.traceName`](/api-reference/assistants/create#request.body.observabilityPlan.traceName) field to make traces easier to identify and filter in your Langfuse dashboard.
+
+The `traceName` field supports [Liquid templates](https://shopify.github.io/liquid/), allowing you to dynamically construct trace names from call and assistant data.
+
+### Available Template Variables
+
+| Variable | Description | Example Value |
+| --- | --- | --- |
+| `{{ call.id }}` | The unique call UUID | `3f4e5a6b-...` |
+| `{{ call.type }}` | The type of call | `inboundPhoneCall`, `outboundPhoneCall`, `webCall` |
+| `{{ assistant.name }}` | The assistant's display name | `Customer Support Bot` |
+| `{{ assistant.id }}` | The assistant's unique ID | `a1b2c3d4-...` |
+
+### Examples
+
+**Simple assistant name prefix:**
+```
+{{ assistant.name }} - {{ call.type }}
+```
+Produces: `Customer Support Bot - inboundPhoneCall`
+
+**Call type grouping:**
+```
+{{ call.type }}/{{ assistant.name }}
+```
+Produces: `outboundPhoneCall/Sales Assistant`
+
+**Include call ID for uniqueness:**
+```
+{{ assistant.name }} ({{ call.id }})
+```
+Produces: `Customer Support Bot (3f4e5a6b-...)`
+
+### API Configuration
+
+You can set the `traceName` field when creating or updating an assistant:
+
+```json
+{
+  "observabilityPlan": {
+    "provider": "langfuse",
+    "traceName": "{{ assistant.name }} - {{ call.type }}",
+    "tags": ["production"],
+    "metadata": {
+      "env": "production"
+    }
+  }
+}
+```
+
+<Info>
+  If `traceName` is not provided, traces default to using the call ID. If a template rendering error occurs, the trace name also falls back safely to the call ID.
+</Info>