diff --git a/charts/substrate/templates/atenet-egress.yaml b/charts/substrate/templates/atenet-egress.yaml
index d62a62207e..c75a29c48a 100644
--- a/charts/substrate/templates/atenet-egress.yaml
+++ b/charts/substrate/templates/atenet-egress.yaml
@@ -70,8 +70,15 @@ data:
         - backends:
           - dynamic: {}
             policies:
+              {{- if .Values.atenetEgress.upstreamTrust.caBundle }}
+              {{- /* No root: the gateway then trusts the native roots, which are
+                the image's public bundle plus upstreamTrust (SSL_CERT_FILE and
+                SSL_CERT_DIR on the agentgateway container). */}}
+              backendTLS: {}
+              {{- else }}
               backendTLS:
                 root: /etc/ssl/certs/ca-certificates.crt
+              {{- end }}
           policies:
             substrateEgress:
               host: {{ include "substrate.fullname" (list "api" .) }}.{{ .Release.Namespace }}.svc:443
@@ -115,6 +122,17 @@ data:
         tcpRoutes:
         - backends:
           - dynamic: {}
+{{- with .Values.atenetEgress.upstreamTrust.caBundle }}
+---
+apiVersion: v1
+kind: ConfigMap
+metadata:
+  name: {{ include "substrate.fullname" (list "atenet-egress-upstream-trust" $) }}
+  namespace: {{ $.Release.Namespace }}
+data:
+  ca.crt: |
+    {{- . | nindent 4 }}
+{{- end }}
 ---
 apiVersion: apps/v1
 kind: Deployment
@@ -132,6 +150,10 @@ spec:
     metadata:
       labels:
         app: atenet-egress
+      {{- with .Values.atenetEgress.upstreamTrust.caBundle }}
+      annotations:
+        checksum/upstream-trust: {{ . | sha256sum }}
+      {{- end }}
     spec:
       serviceAccountName: {{ include "substrate.fullname" (list "atenet-egress" .) }}
       securityContext:
@@ -155,6 +177,14 @@ spec:
               fieldPath: status.podIP
         - name: RUST_LOG
           value: debug
+        {{- if .Values.atenetEgress.upstreamTrust.caBundle }}
+        # Both set: the upstream roots are the image's public bundle plus
+        # upstreamTrust (rustls-native-certs reads the two and nothing else).
+        - name: SSL_CERT_FILE
+          value: /etc/ssl/certs/ca-certificates.crt
+        - name: SSL_CERT_DIR
+          value: /run/egress-upstream-trust
+        {{- end }}
         ports:
         - name: https
           containerPort: 8443
@@ -189,7 +219,17 @@ spec:
         - name: actor-id-ca-certs
           mountPath: /run/actor-id-ca-certs
           readOnly: true
+        {{- if .Values.atenetEgress.upstreamTrust.caBundle }}
+        - name: upstream-trust
+          mountPath: /run/egress-upstream-trust
+          readOnly: true
+        {{- end }}
       volumes:
+      {{- if .Values.atenetEgress.upstreamTrust.caBundle }}
+      - name: upstream-trust
+        configMap:
+          name: {{ include "substrate.fullname" (list "atenet-egress-upstream-trust" .) }}
+      {{- end }}
       - name: egress-mitm
         secret:
           secretName: egress-mitm-ca-pool
diff --git a/charts/substrate/tests/atenet_egress_upstream_trust_test.yaml b/charts/substrate/tests/atenet_egress_upstream_trust_test.yaml
new file mode 100644
index 0000000000..fe796ab881
--- /dev/null
+++ b/charts/substrate/tests/atenet_egress_upstream_trust_test.yaml
@@ -0,0 +1,119 @@
+# Copyright 2026 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#      http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+suite: atenet egress upstream trust
+templates:
+- atenet-egress.yaml
+tests:
+- it: trusts the image's public roots only by default
+  documentSelector:
+    path: kind
+    value: Deployment
+  asserts:
+  - notContains:
+      path: spec.template.spec.containers[0].env
+      content:
+        name: SSL_CERT_DIR
+        value: /run/egress-upstream-trust
+  - notExists:
+      path: spec.template.metadata.annotations
+  - lengthEqual:
+      path: spec.template.spec.volumes
+      count: 5
+
+- it: pins the dynamic HTTPS backend to the image's public bundle by default
+  documentSelector:
+    path: metadata.name
+    value: RELEASE-NAME-atenet-egress-agentgateway-config
+  asserts:
+  - matchRegex:
+      path: data["config.yaml"]
+      pattern: '- dynamic: \{\}\s+policies:\s+backendTLS:\s+root: /etc/ssl/certs/ca-certificates.crt'
+
+- it: renders no upstream trust ConfigMap by default
+  asserts:
+  - containsDocument:
+      kind: ConfigMap
+      apiVersion: v1
+      name: RELEASE-NAME-atenet-egress-upstream-trust
+    not: true
+
+- it: publishes the bundle as a ConfigMap
+  set:
+    atenetEgress.upstreamTrust.caBundle: |
+      -----BEGIN CERTIFICATE-----
+      MIIBlab
+      -----END CERTIFICATE-----
+  documentSelector:
+    path: metadata.name
+    value: RELEASE-NAME-atenet-egress-upstream-trust
+  asserts:
+  - equal:
+      path: data["ca.crt"]
+      value: |
+        -----BEGIN CERTIFICATE-----
+        MIIBlab
+        -----END CERTIFICATE-----
+
+- it: adds the bundle to the public roots of the egress agentgateway and rolls on a change
+  set:
+    atenetEgress.upstreamTrust.caBundle: |
+      -----BEGIN CERTIFICATE-----
+      MIIBlab
+      -----END CERTIFICATE-----
+  documentSelector:
+    path: kind
+    value: Deployment
+  asserts:
+  - contains:
+      path: spec.template.spec.containers[0].env
+      content:
+        name: SSL_CERT_FILE
+        value: /etc/ssl/certs/ca-certificates.crt
+  - contains:
+      path: spec.template.spec.containers[0].env
+      content:
+        name: SSL_CERT_DIR
+        value: /run/egress-upstream-trust
+  - contains:
+      path: spec.template.spec.containers[0].volumeMounts
+      content:
+        name: upstream-trust
+        mountPath: /run/egress-upstream-trust
+        readOnly: true
+  - contains:
+      path: spec.template.spec.volumes
+      content:
+        name: upstream-trust
+        configMap:
+          name: RELEASE-NAME-atenet-egress-upstream-trust
+  - exists:
+      path: spec.template.metadata.annotations["checksum/upstream-trust"]
+
+- it: leaves root out of the dynamic HTTPS backend so the gateway loads the native roots
+  set:
+    atenetEgress.upstreamTrust.caBundle: |
+      -----BEGIN CERTIFICATE-----
+      MIIBlab
+      -----END CERTIFICATE-----
+  documentSelector:
+    path: metadata.name
+    value: RELEASE-NAME-atenet-egress-agentgateway-config
+  asserts:
+  - matchRegex:
+      path: data["config.yaml"]
+      pattern: '- dynamic: \{\}\s+policies:\s+backendTLS: \{\}'
+  - notMatchRegex:
+      path: data["config.yaml"]
+      pattern: /etc/ssl/certs/ca-certificates.crt
diff --git a/charts/substrate/values.yaml b/charts/substrate/values.yaml
index 336fd71cac..023b384ed4 100644
--- a/charts/substrate/values.yaml
+++ b/charts/substrate/values.yaml
@@ -161,6 +161,14 @@ atenetEgress:
       limits:
         cpu: "2"
         memory: 1Gi
+  # Extra CAs the egress gateway trusts on the actors' upstream HTTPS, next to
+  # the public roots of its image: a PEM bundle for model or tool endpoints
+  # behind a private CA (an in-cluster Gateway, a corporate proxy). Empty
+  # trusts the public roots only. The egress gateway terminates the actors' TLS
+  # and dials the upstream itself, so a CA the runtime trusts counts for
+  # nothing here. A change rolls the gateway: the roots are read at start.
+  upstreamTrust:
+    caBundle: ""
 
 # Kubernetes Secret provider and AGW HTTP/HTTPS credential injection.
 # Includes get-only Secret RBAC. HTTPS requires egress-mitm-ca-pool and actor trust.