@@ -54,7 +54,7 @@
 from dataclasses import dataclass
 from datetime import datetime, timezone
 from typing import TYPE_CHECKING, Callable, Iterable, List, Optional
-from wsgiref.simple_server import WSGIServer, make_server
+from wsgiref.simple_server import WSGIRequestHandler, WSGIServer, make_server
 
 import psutil
 
@@ -585,6 +585,22 @@ def init_worker_freshness_monitoring(store: "FeatureStore"):
         t.start()
 
 
+class _QuietWSGIRequestHandler(WSGIRequestHandler):
+    """Request handler that does not log each scrape to stderr.
+
+    The metrics server runs as a thread in the Gunicorn master, which forks
+    the workers. The default handler writes an access-log line to stderr for
+    every request; a fork while that thread holds the stderr buffer lock
+    leaves the new worker with the lock held forever, and the worker hangs
+    on its first log line ("Booting worker") before it serves anything.
+    Same class of problem as #6647. prometheus_client's own server uses a
+    silent handler for the same reason.
+    """
+
+    def log_message(self, format, *args):  # noqa: A002 - signature of the base class
+        pass
+
+
 def _make_metrics_httpd(port: int, app: Callable[..., Iterable[bytes]]) -> WSGIServer:
     """Build the metrics HTTP server, dual-stack ("::") when the host
     supports IPv6, or IPv4-only (falls back to `make_server`'s default
@@ -593,7 +609,7 @@ def _make_metrics_httpd(port: int, app: Callable[..., Iterable[bytes]]) -> WSGIS
     from feast import utils
 
     if not utils._ipv6_available():
-        return make_server("", port, app)
+        return make_server("", port, app, handler_class=_QuietWSGIRequestHandler)
 
     class DualStackWSGIServer(WSGIServer):
         address_family = socket.AF_INET6
@@ -602,7 +618,13 @@ def server_bind(self) -> None:
             self.socket.setsockopt(socket.IPPROTO_IPV6, socket.IPV6_V6ONLY, 0)
             super().server_bind()
 
-    return make_server("::", port, app, server_class=DualStackWSGIServer)
+    return make_server(
+        "::",
+        port,
+        app,
+        server_class=DualStackWSGIServer,
+        handler_class=_QuietWSGIRequestHandler,
+    )
 
 
 def start_metrics_server(
 
@@ -22,6 +22,7 @@
 import pytest
 
 from feast.metrics import (
+    _make_metrics_httpd,
     emit_offline_audit_log,
     emit_online_audit_log,
     feature_freshness_seconds,
@@ -2085,3 +2086,26 @@ def test_start_metrics_server_wires_make_metrics_httpd(mocker):
             break
         time.sleep(0.01)
     assert mock_httpd.serve_forever.called
+
+
+class TestMetricsHttpdDoesNotLog:
+    """The metrics server must not write to stderr per request (fork safety, see _QuietWSGIRequestHandler)."""
+
+    def test_scrape_writes_nothing_to_stderr(self, capsys):
+        def app(environ, start_response):
+            start_response("200 OK", [("Content-Type", "text/plain")])
+            return [b"ok"]
+
+        httpd = _make_metrics_httpd(0, app)
+        port = httpd.server_address[1]
+        server = threading.Thread(target=httpd.handle_request, daemon=True)
+        server.start()
+        try:
+            conn = http.client.HTTPConnection("127.0.0.1", port, timeout=5)
+            conn.request("GET", "/metrics")
+            assert conn.getresponse().status == 200
+            server.join(timeout=5)
+        finally:
+            httpd.server_close()
+
+        assert "GET /metrics" not in capsys.readouterr().err