diff --git a/agent/chat_completion_helpers.py b/agent/chat_completion_helpers.py
index 56228ac09..8392a76a3 100644
--- a/agent/chat_completion_helpers.py
+++ b/agent/chat_completion_helpers.py
@@ -1241,7 +1241,17 @@ def try_activate_fallback(agent, reason: "FailoverReason | None" = None) -> bool
         _fb_is_azure = agent._is_azure_openai_url(fb_base_url)
         if fb_provider == "openai-codex":
             fb_api_mode = "codex_responses"
-        elif fb_provider == "anthropic" or fb_base_url.rstrip("/").lower().endswith("/anthropic"):
+        elif (
+            fb_provider == "anthropic"
+            or fb_base_url.rstrip("/").lower().endswith("/anthropic")
+            or base_url_hostname(fb_base_url) == "api.anthropic.com"
+        ):
+            # Custom providers (e.g. cron-anthropic) point at the native
+            # api.anthropic.com host with no "/anthropic" path suffix, so the
+            # name/suffix checks above miss them and they default to
+            # chat_completions → POST /v1/chat/completions → 404. Match the
+            # host the same way determine_api_mode() and _detect_api_mode_for_url()
+            # do on the primary path. (#32243, #49247)
             fb_api_mode = "anthropic_messages"
         elif _fb_is_azure:
             # Azure OpenAI serves gpt-5.x on /chat/completions — does NOT