feat(moe): add megamoe a2a backend plumbing

Add the MegaMoE A2A backend name to server argument choices and MoE backend enums, wire the startup handling that forces ep_size to tp_size, and add the env flags used by the later MegaMoE forward and weight layout work. Treat MegaMoE as a dispatcher bypass so it does not enter DeepEP dispatcher logic.\n\nConstraint: Applies on top of origin/rc/v0.1 for GLM 5.2 MegaMoE adaptation.\nFeature-flag: --moe-a2a-backend megamoe and SGLANG_OPT_USE_DEEPGEMM_MEGA_MOE.\nConflict-hotspots: python/sglang/srt/server_args.py; python/sglang/srt/layers/moe/utils.py; python/sglang/srt/layers/moe/fused_moe_triton/layer.py\nScope-risk: medium\nTested: git diff --check\nTested: python3 -c ast.parse on modified Python files

python/sglang/srt/environ.py

@@ -506,6 +506,13 @@ class Envs:
     SGLANG_DG_USE_NVRTC = EnvBool(False)
     SGLANG_USE_DEEPGEMM_BMM = EnvBool(False)
 
+    # DeepGEMM MegaMoE
+    SGLANG_OPT_USE_DEEPGEMM_MEGA_MOE = EnvBool(False)
+    SGLANG_OPT_DEEPGEMM_MEGA_MOE_NUM_MAX_TOKENS_PER_RANK = EnvInt(1024)
+    SGLANG_OPT_DEEPGEMM_MEGA_MOE_USE_FP4_ACTS = EnvBool(False)
+    SGLANG_OPT_DEEPGEMM_MEGA_MOE_USE_MXF4_KIND = EnvBool(False)
+    SGLANG_OPT_FIX_MEGA_MOE_MEMORY = EnvBool(False)
+
     # DeepSeek MHA Optimization
     SGLANG_CHUNKED_PREFIX_CACHE_THRESHOLD = EnvInt(8192)
 

python/sglang/srt/layers/moe/fused_moe_triton/layer.py

@@ -94,7 +94,7 @@ logger = logging.getLogger(__name__)
 
 def create_moe_dispatcher(moe_runner_config: MoeRunnerConfig) -> BaseDispatcher:
     a2a_backend = get_moe_a2a_backend()
-    if a2a_backend.is_none():
+    if a2a_backend.is_none() or a2a_backend.is_megamoe():
         return StandardDispatcher(moe_runner_config)
     elif (
         a2a_backend.is_deepep()

python/sglang/srt/layers/moe/utils.py

@@ -26,6 +26,7 @@ class MoeA2ABackend(Enum):
     MORI = "mori"
     ASCEND_FUSEEP = "ascend_fuseep"
     FLASHINFER = "flashinfer"
+    MEGAMOE = "megamoe"
 
     @classmethod
     def _missing_(cls, value):
@@ -57,6 +58,9 @@ class MoeA2ABackend(Enum):
     def is_mori(self):
         return self == MoeA2ABackend.MORI
 
+    def is_megamoe(self):
+        return self == MoeA2ABackend.MEGAMOE
+
 
 class MoeRunnerBackend(Enum):
 
@@ -244,6 +248,22 @@ def get_deepep_config() -> str:
     return DEEPEP_CONFIG
 
 
+def is_deepep_class_backend() -> bool:
+    """Check if the MoE backend uses DeepEP-family dispatcher semantics."""
+    b = get_moe_a2a_backend()
+    return b.is_deepep() or b.is_mooncake() or b.is_mori()
+
+
+def uses_per_rank_fused_shared_slots() -> bool:
+    """Check whether fused shared experts use per-rank physical slots."""
+    return is_deepep_class_backend() or get_moe_a2a_backend().is_megamoe()
+
+
+def has_per_rank_fused_shared_slots(num_fused_shared_experts: int) -> bool:
+    """Check whether this layer has fused shared experts in per-rank slots."""
+    return num_fused_shared_experts > 0 and uses_per_rank_fused_shared_slots()
+
+
 def is_tbo_enabled() -> bool:
     global IS_TBO_ENABLED
     if IS_TBO_ENABLED is None:

python/sglang/srt/server_args.py

@@ -218,6 +218,7 @@ MOE_A2A_BACKEND_CHOICES = [
     "mori",
     "ascend_fuseep",
     "flashinfer",
+    "megamoe",
 ]
 
 FP8_GEMM_RUNNER_BACKEND_CHOICES = [
@@ -3030,6 +3031,25 @@ class ServerArgs:
             )
 
     def _handle_a2a_moe(self):
+        if (
+            envs.SGLANG_OPT_USE_DEEPGEMM_MEGA_MOE.get()
+            and self.moe_a2a_backend != "megamoe"
+        ):
+            self.moe_a2a_backend = "megamoe"
+            logger.info(
+                "SGLANG_OPT_USE_DEEPGEMM_MEGA_MOE is set, "
+                "auto-configuring --moe-a2a-backend megamoe."
+            )
+
+        if self.moe_a2a_backend == "megamoe":
+            self.ep_size = self.tp_size
+            if not envs.SGLANG_OPT_FIX_MEGA_MOE_MEMORY.is_set():
+                envs.SGLANG_OPT_FIX_MEGA_MOE_MEMORY.set(True)
+            logger.warning(
+                f"MegaMoE is enabled. The expert parallel size is adjusted "
+                f"to be the same as the tensor parallel size[{self.tp_size}]."
+            )
+
         if self.moe_a2a_backend == "deepep":
             if self.deepep_mode == "normal":
                 logger.warning("Cuda graph is disabled because deepep_mode=`normal`")