diff --git a/run_agent.py b/run_agent.py
index cb39669ece7..8908562b38c 100644
--- a/run_agent.py
+++ b/run_agent.py
@@ -13117,6 +13117,21 @@ class AIAgent:
                         "does not support multimodal",
                         "does not support vision",
                         "model does not support image",
+                        # ChatGPT-account Codex backend
+                        # (https://chatgpt.com/backend-api/codex) rejects
+                        # data:image/...base64 URLs in input_image fields
+                        # with HTTP 400 "Invalid 'input[N].content[K].image_url'.
+                        # Expected a valid URL, but got a value with an
+                        # invalid format." The OpenAI Responses API on the
+                        # public endpoint accepts data URLs, but the
+                        # ChatGPT-account variant does not. Without this
+                        # phrase the agent cascaded into compression /
+                        # context-too-large recovery instead of just
+                        # stripping the images. Match is narrow on
+                        # purpose — keyed on the field-path apostrophe so
+                        # we don't false-trip on other URL validation
+                        # errors. (issue #23570)
+                        "image_url'. expected",
                     )
                     _err_lower = _err_body.lower()
                     _looks_like_image_rejection = any(
diff --git a/tests/run_agent/test_image_rejection_fallback.py b/tests/run_agent/test_image_rejection_fallback.py
index e52719d9742..d1d6c7ff028 100644
--- a/tests/run_agent/test_image_rejection_fallback.py
+++ b/tests/run_agent/test_image_rejection_fallback.py
@@ -194,6 +194,7 @@ class TestImageRejectionPhraseIsolation:
         "does not support multimodal",
         "does not support vision",
         "model does not support image",
+        "image_url'. expected",
     )
 
     def _matches(self, body: str) -> bool:
@@ -238,6 +239,29 @@ class TestImageRejectionPhraseIsolation:
             "This model does not support images",
             "vision is not supported on this endpoint",
             "model does not support image input",
+            # ChatGPT-account Codex backend (issue #23570) — rejects
+            # data:image/...base64 URLs in input_image fields. Without this
+            # match the agent cascaded into compression / context-too-large
+            # recovery instead of just stripping the images.
+            "Invalid 'input[56].content[1].image_url'. Expected a valid URL, but got a value with an invalid format.",
         ]
         for body in bodies:
             assert self._matches(body) is True, f"false negative on: {body}"
+
+    def test_codex_data_url_rejection_does_not_false_match_other_url_errors(self):
+        """The narrow 'image_url'. expected' phrase (keyed on the
+        field-path apostrophe used in the Codex Responses error format)
+        must NOT trip on URL validation errors that aren't about
+        image_url specifically. See issue #23570 for the original error.
+        """
+        bodies = [
+            # Generic URL validation errors — should NOT trip
+            "Invalid webhook_url. Must be a valid URL.",
+            "Expected a valid URL but got an empty string.",
+            "redirect_uri does not look like a valid URL.",
+            # An image_url error worded differently — also should not trip
+            # the narrow phrase (a separate phrase would be needed)
+            "image_url field cannot be empty",
+        ]
+        for body in bodies:
+            assert self._matches(body) is False, f"false positive on: {body}"