diff --git a/helm/echo/templates/_helpers.tpl b/helm/echo/templates/_helpers.tpl
index 9bbbc96..95ec6bb 100644
--- a/helm/echo/templates/_helpers.tpl
+++ b/helm/echo/templates/_helpers.tpl
@@ -101,6 +101,22 @@ Common environment variables (including feature flags and non-sensitive config)
 - name: ASSEMBLYAI_WEBHOOK_URL
   value: {{ . | quote }}
 {{- end }}
+{{- with (default "" .Values.common.env.LLM__OPEN_SOURCE__MODEL) }}
+- name: LLM__OPEN_SOURCE__MODEL
+  value: {{ . | quote }}
+{{- end }}
+{{- with (default "" .Values.common.env.LLM__OPEN_SOURCE__VERTEX_LOCATION) }}
+- name: LLM__OPEN_SOURCE__VERTEX_LOCATION
+  value: {{ . | quote }}
+{{- end }}
+{{- with (default "" .Values.common.env.LLM__OPEN_SOURCE__VERTEX_PROJECT) }}
+- name: LLM__OPEN_SOURCE__VERTEX_PROJECT
+  value: {{ . | quote }}
+{{- end }}
+{{- with (default "" .Values.common.env.LLM__OPEN_SOURCE__API_BASE) }}
+- name: LLM__OPEN_SOURCE__API_BASE
+  value: {{ . | quote }}
+{{- end }}
 {{- end }}
 
 {{/*
@@ -201,4 +217,15 @@ All secret-based environment variables
       name: echo-backend-secrets
       key: ASSEMBLYAI_WEBHOOK_SECRET
       optional: true
+- name: LLM__OPEN_SOURCE__GCP_SA_JSON
+  valueFrom:
+    secretKeyRef:
+      name: echo-backend-secrets
+      key: GCP_SA_JSON
+- name: LLM__OPEN_SOURCE__API_KEY
+  valueFrom:
+    secretKeyRef:
+      name: echo-backend-secrets
+      key: LLM__OPEN_SOURCE__API_KEY
+      optional: true
 {{- end }}
diff --git a/helm/echo/values-extended-env.yaml b/helm/echo/values-extended-env.yaml
index a1074ef..c0acd7b 100644
--- a/helm/echo/values-extended-env.yaml
+++ b/helm/echo/values-extended-env.yaml
@@ -30,3 +30,9 @@ common:
 
     EMBEDDING_MODEL: "vertex_ai/text-embedding-004"
     EMBEDDING_BASE_URL: "https://europe-west4-aiplatform.googleapis.com"
+
+    # Open Source model configurations for preference A/B testing
+    LLM__OPEN_SOURCE__MODEL: "vertex_ai/mistral-large"
+    LLM__OPEN_SOURCE__VERTEX_LOCATION: "europe-west4"
+    LLM__OPEN_SOURCE__VERTEX_PROJECT: ""
+    LLM__OPEN_SOURCE__API_BASE: ""