diff --git a/.env.example b/.env.example
index a2f3ebf..7992677 100644
--- a/.env.example
+++ b/.env.example
@@ -7,9 +7,10 @@
 # Gemini (pick ONE of the two paths below)
 # ----------------------------------------------------------------------
 
-# Path A — Gemini Developer API key
+# Path A: Gemini Developer API key.
 # GEMINI_API_KEY=
-# GOOGLE_API_KEY=
+# (``GOOGLE_API_KEY`` is also accepted as a fallback for
+# compatibility with Google's official SDK convention.)
 
 # Path B — Vertex AI project (requires ``gcloud auth
 # application-default login`` to have been run)
diff --git a/README.md b/README.md
index 5321bc8..8f78f15 100644
--- a/README.md
+++ b/README.md
@@ -117,7 +117,10 @@ Either set an API key:
 
 | Variable | Required | Purpose |
 | --- | --- | --- |
-| `GEMINI_API_KEY` or `GOOGLE_API_KEY` | yes (one of the two) | Gemini API key |
+| `GEMINI_API_KEY` | yes | Gemini API key |
+
+`GOOGLE_API_KEY` is also accepted as a fallback for compatibility
+with Google's official SDK convention.
 
 …or use a Vertex AI project (after running `gcloud auth
 application-default login`):