diff --git a/hermes_cli/config.py b/hermes_cli/config.py
index d4e9ed843caa..cc03c5a57b5c 100644
--- a/hermes_cli/config.py
+++ b/hermes_cli/config.py
@@ -8209,6 +8209,25 @@ def save_env_value(key: str, value: str):
     invalidate_env_cache()
 
 
+def custom_endpoint_key_env(identity: str) -> str:
+    """Env var name holding a custom endpoint's API key.
+
+    ``identity`` is whatever names the endpoint on the calling path — the
+    Desktop panel's endpoint id, or ``host:port`` for the CLI setup flow.
+    Two properties matter:
+
+    - It keys off the endpoint's own identity, not just its hostname, so two
+      endpoints on one host (``127.0.0.1:8000`` and ``:8001``) get separate
+      slots instead of the second save clobbering the first's credential.
+    - The fixed ``HERMES_CUSTOM_`` prefix keeps the result a valid POSIX name
+      even when the slug starts with a digit, which every IP-based local
+      endpoint does (``127.0.0.1`` → ``127_0_0_1``). ``save_env_value``
+      rejects digit-leading names outright.
+    """
+    slug = re.sub(r"[^A-Z0-9]+", "_", str(identity or "").upper()).strip("_")
+    return f"HERMES_CUSTOM_{slug}_API_KEY" if slug else "HERMES_CUSTOM_API_KEY"
+
+
 def remove_env_value(key: str) -> bool:
     """Remove a key from ~/.hermes/.env and os.environ.