diff --git a/lambdas/po/email_processor/handler.py b/lambdas/po/email_processor/handler.py
index 9c5b620..6063c65 100644
--- a/lambdas/po/email_processor/handler.py
+++ b/lambdas/po/email_processor/handler.py
@@ -211,14 +211,21 @@ The Coupa commodity/category field if present in the email (e.g., "Maintenance -
 
 
 def get_anthropic_client() -> anthropic.Anthropic:
-    """Create Anthropic client, fetching API key from Secrets Manager."""
-    if ANTHROPIC_API_KEY_SECRET_ARN:
-        secrets = boto3.client("secretsmanager")
-        secret = secrets.get_secret_value(SecretId=ANTHROPIC_API_KEY_SECRET_ARN)
-        api_key = secret["SecretString"]
-        return anthropic.Anthropic(api_key=api_key)
-    # Fall back to ANTHROPIC_API_KEY env var (for local testing)
-    return anthropic.Anthropic()
+    """Create Anthropic client, fetching API key from Secrets Manager.
+
+    Requires ANTHROPIC_API_KEY_SECRET_ARN to be set. The previous silent
+    fallback to a plaintext ANTHROPIC_API_KEY env var is removed: a misconfigured
+    deploy must fail loudly rather than quietly run on an unmanaged key.
+    """
+    if not ANTHROPIC_API_KEY_SECRET_ARN:
+        raise RuntimeError(
+            "ANTHROPIC_API_KEY_SECRET_ARN is not set; refusing to fall back to a "
+            "plaintext API key. Configure the Secrets Manager ARN."
+        )
+    secrets = boto3.client("secretsmanager")
+    secret = secrets.get_secret_value(SecretId=ANTHROPIC_API_KEY_SECRET_ARN)
+    api_key = secret["SecretString"]
+    return anthropic.Anthropic(api_key=api_key)
 
 
 def parse_raw_email(raw_bytes: bytes) -> dict:
diff --git a/lambdas/wo/email_processor/handler.py b/lambdas/wo/email_processor/handler.py
index 2abdc8f..f51cc5e 100644
--- a/lambdas/wo/email_processor/handler.py
+++ b/lambdas/wo/email_processor/handler.py
@@ -66,14 +66,21 @@ Rules:
 
 
 def get_anthropic_client() -> anthropic.Anthropic:
-    """Create Anthropic client, fetching API key from Secrets Manager if configured."""
-    if ANTHROPIC_API_KEY_SECRET_ARN:
-        secrets = boto3.client("secretsmanager")
-        secret = secrets.get_secret_value(SecretId=ANTHROPIC_API_KEY_SECRET_ARN)
-        api_key = secret["SecretString"]
-        return anthropic.Anthropic(api_key=api_key)
-    # Fall back to ANTHROPIC_API_KEY env var (for local testing)
-    return anthropic.Anthropic()
+    """Create Anthropic client, fetching API key from Secrets Manager.
+
+    Requires ANTHROPIC_API_KEY_SECRET_ARN to be set. The previous silent
+    fallback to a plaintext ANTHROPIC_API_KEY env var is removed: a misconfigured
+    deploy must fail loudly rather than quietly run on an unmanaged key.
+    """
+    if not ANTHROPIC_API_KEY_SECRET_ARN:
+        raise RuntimeError(
+            "ANTHROPIC_API_KEY_SECRET_ARN is not set; refusing to fall back to a "
+            "plaintext API key. Configure the Secrets Manager ARN."
+        )
+    secrets = boto3.client("secretsmanager")
+    secret = secrets.get_secret_value(SecretId=ANTHROPIC_API_KEY_SECRET_ARN)
+    api_key = secret["SecretString"]
+    return anthropic.Anthropic(api_key=api_key)
 
 
 def parse_raw_email(raw_bytes: bytes) -> dict: