diff --git a/python/sglang/srt/server_args.py b/python/sglang/srt/server_args.py
index 87523e5d4..997f6f389 100644
--- a/python/sglang/srt/server_args.py
+++ b/python/sglang/srt/server_args.py
@@ -1795,13 +1795,28 @@ class ServerArgs:
                             "Context parallel feature is still under experiment. It has only been verified on Hopper platform."
                         )
                         if self.nsa_prefill_cp_mode == "in-seq-split":
-                            # TODO Supports moe_dense_tp_size != 1, kv cache dtype = "fp8",moe_a2a_backend non-deepep and cross-machine operation .
+                            # TODO Supports moe_dense_tp_size != 1, kv cache dtype = "fp8", and cross-machine operation .
                             self.enable_dp_attention = True
                             self.moe_dense_tp_size = 1
-                            self.moe_a2a_backend = "deepep"
+                            # B300 decouple (Strategy B): only force the historical
+                            # deepep CP path when no MoE backend was selected
+                            # explicitly. With an explicit runner (e.g.
+                            # flashinfer_trtllm) keep a2a as "none"/"flashinfer"
+                            # so CP runs on the standard/allgather path.
+                            if (
+                                self.moe_a2a_backend == "none"
+                                and self.moe_runner_backend == "auto"
+                            ):
+                                self.moe_a2a_backend = "deepep"
+                            if self.moe_a2a_backend not in {"deepep", "flashinfer", "none"}:
+                                raise ValueError(
+                                    "For NSA prefill CP in-seq split mode, moe_a2a_backend "
+                                    "must be one of {'deepep', 'flashinfer', 'none'}."
+                                )
                             self.ep_size = self.tp_size
                             logger.warning(
-                                "For in-seq split mode, we have the following restrictions: moe_dense_tp_size == 1, moe_a2a_backend == deepep, ep_size == tp_size, batch_size == 1"
+                                "For in-seq split mode: moe_dense_tp_size == 1, moe_a2a_backend in "
+                                "{'deepep', 'flashinfer', 'none'}, ep_size == tp_size, batch_size == 1"
                             )
                         else:
                             self.enable_dp_attention = True
@@ -1809,9 +1824,14 @@ class ServerArgs:
                             assert (
                                 self.dp_size == 1
                             ), "For round-robin split mode, dp attention is not supported."
-                        assert (
-                            self.tp_size == 8
-                        ), "Current multi-machine CP support suffers from precision issues. So context parallel only support Single machine(tp_size == 8)"
+                        # B300 decouple: allow single-node tp4/CP4 (target PD) in
+                        # addition to tp8/CP8. CP code is parametric in cp_size; the
+                        # tp_size%attn_cp_size and tp_size%(dp_size*attn_cp_size)
+                        # divisibility asserts below still guard validity.
+                        assert self.tp_size in (4, 8), (
+                            "Multi-machine CP has precision issues; context parallel only "
+                            f"supports a single machine (tp_size in {{4, 8}}), got {self.tp_size}."
+                        )
                         self.attn_cp_size = self.tp_size
 
                         logger.warning(