diff --git a/python/sglang/srt/server_args.py b/python/sglang/srt/server_args.py
index d87c5e5da2b4..d67f5890dd9e 100644
--- a/python/sglang/srt/server_args.py
+++ b/python/sglang/srt/server_args.py
@@ -5740,6 +5740,13 @@ def _handle_model_specific_adjustments(self):
                 "intel_xpu",
                 "intel_amx",
             )
+            # Seam: a plugin-registered backend declares its own sliding
+            # window and KV-sharing support.
+            from sglang.srt.layers.attention.attention_registry import (
+                PLUGIN_ATTENTION_BACKENDS,
+            )
+
+            accepted_backends += tuple(sorted(PLUGIN_ATTENTION_BACKENDS))
             assert (
                 prefill_backend in accepted_backends
                 and decode_backend in accepted_backends