--- baked-ours/models/deepseek_v4_1/attention.py	2026-09-10 20:13:20.000000000 +0200
+++ baked/models/deepseek_v4_1/attention.py	2026-09-11 10:13:47.000000000 +0200
@@ -42,7 +42,7 @@
     VllmConfig,
     get_current_vllm_config,
 )
-from vllm.distributed import get_tensor_model_parallel_world_size
+from vllm.distributed import get_dcp_group, get_tensor_model_parallel_world_size
 from vllm.forward_context import get_forward_context
 from vllm.logger import init_logger
 from vllm.model_executor.layers.attention_layer_base import AttentionLayerBase
@@ -172,6 +172,13 @@
     # workspace allocated in _forward_prefill and is also read by the dummy-run
     # path to pre-reserve that workspace.
     PREFILL_CHUNK_SIZE: ClassVar[int] = 4
+    # DCP contract, mirroring AttentionImpl (v1/attention/backend.py): the
+    # V4.1 layer runs its own forward (no AttentionImpl), so
+    # check_attention_cp_compatibility reads these from the layer. A platform
+    # subclass that implements the per-rank partial attention + LSE combine
+    # sets can_return_lse_for_decode = True (SM120 FlashInfer).
+    can_return_lse_for_decode: ClassVar[bool] = False
+    supports_mtp_with_cp_non_trivial_interleave_size: ClassVar[bool] = False
 
     @classmethod
     @abstractmethod
@@ -226,6 +233,22 @@
         self.n_heads = config.num_attention_heads
         assert self.n_heads % tp_size == 0
         self.n_local_heads = self.n_heads // tp_size
+        # Decode context parallelism: compressed/indexer caches are sharded over
+        # compressed states across the DCP group (a subset of the TP ranks),
+        # SWA caches are replicated; the platform subclass gathers queries and
+        # combines per-rank partial attention (DCP2-PLAN.md).
+        parallel_config = vllm_config.parallel_config
+        self.dcp_world_size = parallel_config.decode_context_parallel_size
+        self.dcp_rank = get_dcp_group().rank_in_group if self.dcp_world_size > 1 else 0
+        self.cp_kv_cache_interleave_size = parallel_config.cp_kv_cache_interleave_size
+        self.need_to_return_lse_for_decode = (
+            self.dcp_world_size > 1 and self.can_return_lse_for_decode
+        )
+        if self.dcp_world_size > 1 and self.cp_kv_cache_interleave_size != 1:
+            raise NotImplementedError(
+                "DeepSeek-V4.1 DCP supports cp_kv_cache_interleave_size=1 only "
+                f"(got {self.cp_kv_cache_interleave_size})."
+            )
         self.q_lora_rank = config.q_lora_rank
         self.o_lora_rank = config.o_lora_rank
         self.head_dim = config.head_dim