diff --git a/.ado/ci.yml b/.ado/ci.yml
index b6b8707b..67fee63a 100644
--- a/.ado/ci.yml
+++ b/.ado/ci.yml
@@ -17,6 +17,14 @@ variables:
     value: none # Disable usage telemetry for internal test pipelines
   - name: PYTEST_MAX_PARALLEL_TESTS
     value: "auto"
+  # Azure Artifacts feed (with a PyPI upstream source) that pip restores from, so the
+  # build does not connect directly to public pypi.org / files.pythonhosted.org (CFS).
+  # Project-scoped: "<Project>/<FeedName>".
+  - name: PipFeed
+    value: "AzureQuantum/azure-quantum"
+  # Stop pip from contacting pypi.org for its "is there a newer pip?" self-check.
+  - name: PIP_DISABLE_PIP_VERSION_CHECK
+    value: "1"
 
 jobs:
   - job: "Build_Azure_Quantum_Python"
@@ -30,6 +38,12 @@ jobs:
           versionSpec: "3.11"
         displayName: Set Python version
 
+      - task: PipAuthenticate@1
+        displayName: Authenticate pip to Azure Artifacts feed
+        inputs:
+          artifactFeeds: $(PipFeed)
+          onlyAddExtraIndex: false
+
       - script: |
           pip install wheel
         displayName: Install wheel
@@ -59,6 +73,12 @@ jobs:
           versionSpec: "3.11"
         displayName: Set Python version
 
+      - task: PipAuthenticate@1
+        displayName: Authenticate pip to Azure Artifacts feed
+        inputs:
+          artifactFeeds: $(PipFeed)
+          onlyAddExtraIndex: false
+
       - script: |
           python -m pip install --upgrade pip
           pip install pytest pytest-azurepipelines pytest-cov pytest-xdist tox
diff --git a/.ado/publish.yml b/.ado/publish.yml
index 5914f451..63112b6c 100644
--- a/.ado/publish.yml
+++ b/.ado/publish.yml
@@ -44,6 +44,10 @@ variables:
     value: "auto"
   - name: PipFeed
     value: "AzureQuantum/azure-quantum"
+  # Stop pip from contacting pypi.org for its "is there a newer pip?" self-check.
+  # This version check ignores PIP_INDEX_URL and is a common lingering CFS offender.
+  - name: PIP_DISABLE_PIP_VERSION_CHECK
+    value: "1"
 
 resources:
   repositories:
@@ -140,6 +144,7 @@ extends:
 
               - script: |
                   cd $(Build.SourcesDirectory)/azure-quantum
+                  python -c "import os, urllib.parse as u; h = u.urlsplit(os.environ.get('PIP_INDEX_URL', '')).hostname or '(unset -> default pypi.org)'; print('pip index host:', h)"
                   tox -e py311-qiskit1,py311-qiskit2
                 displayName: Run Qiskit matrix tests
 
diff --git a/azure-quantum/tox.ini b/azure-quantum/tox.ini
index f17477b5..46835443 100644
--- a/azure-quantum/tox.ini
+++ b/azure-quantum/tox.ini
@@ -13,6 +13,13 @@ basepython =
 passenv =
     PIP_INDEX_URL
     PIP_EXTRA_INDEX_URL
+# Explicitly re-assert the feed index inside each isolated environment. Relying on
+# passenv alone proved unreliable (tox's inner pip fell back to pypi.org). The
+# fallback keeps local dev working when PIP_INDEX_URL is unset. Also disable pip's
+# pypi.org version self-check, which ignores the index URL.
+setenv =
+    PIP_INDEX_URL = {env:PIP_INDEX_URL:https://pypi.org/simple}
+    PIP_DISABLE_PIP_VERSION_CHECK = 1
 allowlist_externals = pytest
 deps =
     qiskit1: qiskit<2