Support NextN (MTP) speculative decoding for DeepSeek-V3/R1 (#3582)

python/sglang/srt/speculative/eagle_worker.py

@@ -24,6 +24,7 @@ from sglang.srt.speculative.eagle_utils import (
     fast_topk,
     select_top_k_tokens,
 )
+from sglang.srt.speculative.spec_info import SpeculativeAlgorithm
 
 logger = logging.getLogger(__name__)
 
@@ -57,11 +58,15 @@ class EAGLEWorker(TpModelWorker):
         # Parse arguments
         self.topk = server_args.speculative_eagle_topk
         self.speculative_num_steps = server_args.speculative_num_steps
+        self.speculative_algorithm = SpeculativeAlgorithm.from_string(
+            server_args.speculative_algorithm
+        )
         self.server_args = server_args
 
         # Share the embedding and lm_head
-        embed, head = self.target_worker.model_runner.model.get_embed_and_head()
-        self.model_runner.model.set_embed_and_head(embed, head)
+        if not self.speculative_algorithm.is_nextn():
+            embed, head = self.target_worker.model_runner.model.get_embed_and_head()
+            self.model_runner.model.set_embed_and_head(embed, head)
         self.model_runner.server_args.disable_cuda_graph = backup_disable_cuda_graph
 
         # Create multi-step attn backends and cuda graph runners

python/sglang/srt/speculative/spec_info.py

@@ -5,18 +5,28 @@ class SpeculativeAlgorithm(IntEnum):
     NONE = auto()
     EAGLE = auto()
 
+    # NEXTN spec decoding is for DeepSeek V3/R1
+    # currently it's implemented based on EAGLE
+    NEXTN = auto()
+
     def is_none(self):
         return self == SpeculativeAlgorithm.NONE
 
     def is_eagle(self):
-        return self == SpeculativeAlgorithm.EAGLE
+        return self == SpeculativeAlgorithm.EAGLE or self == SpeculativeAlgorithm.NEXTN
+
+    def is_nextn(self):
+        return self == SpeculativeAlgorithm.NEXTN
 
     @staticmethod
     def from_string(name: str):
         name_map = {
             "EAGLE": SpeculativeAlgorithm.EAGLE,
+            "NEXTN": SpeculativeAlgorithm.NEXTN,
             None: SpeculativeAlgorithm.NONE,
         }
+        if name is not None:
+            name = name.upper()
         return name_map[name]