From 392841f47cb7ef214601eeb528906a0abba02471 Mon Sep 17 00:00:00 2001
From: Yash Akhauri <akhauri.yash@gmail.com>
Date: Thu, 3 Sep 2026 08:53:16 -0700
Subject: [PATCH] [Bugfix] Support K2 Horizon MoE without MoVA (#37825)

Co-authored-by: BBuf <1182563586@qq.com>
---
 python/sglang/srt/models/xllm.py | 38 +++++++++++++++++++++++---------
 1 file changed, 28 insertions(+), 10 deletions(-)

diff --git a/python/sglang/srt/models/xllm.py b/python/sglang/srt/models/xllm.py
index 4fa46971a..10cc99332 100644
--- a/python/sglang/srt/models/xllm.py
+++ b/python/sglang/srt/models/xllm.py
@@ -188,6 +188,17 @@ def _normalize_k2_horizon_config(config: PretrainedConfig) -> None:
             f"got {mova_num_experts!r}."
         )
     is_mova = mova_num_experts > 0
+    num_experts = getattr(config, "num_experts", 0)
+    if (
+        isinstance(num_experts, bool)
+        or not isinstance(num_experts, int)
+        or num_experts < 0
+    ):
+        raise ValueError(
+            "K2Horizon num_experts must be a non-negative integer, "
+            f"got {num_experts!r}."
+        )
+    has_moe_ffn = num_experts > 0
 
     if is_mova:
         if _get_xllm_source_router_gemm_partitions(config) is None:
@@ -247,14 +258,21 @@ def _normalize_k2_horizon_config(config: PretrainedConfig) -> None:
             target_name="num_values_per_tok",
             value=0,
         )
-        for field in ("num_experts", "num_experts_per_tok", "num_shared_experts"):
-            value = getattr(config, field, 0)
-            if isinstance(value, bool) or not isinstance(value, int) or value != 0:
-                raise ValueError(f"Dense K2Horizon requires {field}=0, got {value!r}")
-            # Some dense exports omit the MoE-only fields. Downstream model
-            # construction reads them directly, so materialize the validated
-            # dense defaults instead of relying on getattr fallbacks forever.
-            setattr(config, field, 0)
+        if not has_moe_ffn:
+            for field in (
+                "num_experts",
+                "num_experts_per_tok",
+                "num_shared_experts",
+            ):
+                value = getattr(config, field, 0)
+                if isinstance(value, bool) or not isinstance(value, int) or value != 0:
+                    raise ValueError(
+                        f"Dense K2Horizon requires {field}=0, got {value!r}"
+                    )
+                # Some dense exports omit the MoE-only fields. Downstream model
+                # construction reads them directly, so materialize the validated
+                # dense defaults instead of relying on getattr fallbacks forever.
+                setattr(config, field, 0)
         if getattr(config, "query_key_norm", False):
             raise ValueError(
                 "Dense K2Horizon native loading does not support query/key "
@@ -489,7 +507,7 @@ def _normalize_k2_horizon_config(config: PretrainedConfig) -> None:
                 "K2Horizon MoVA requires mlp_only_layers to be a contiguous "
                 f"prefix starting at zero, got {list(mlp_only_layers)}"
             )
-        if not is_mova and list(mlp_only_layers) != list(
+        if not has_moe_ffn and list(mlp_only_layers) != list(
             range(config.num_hidden_layers)
         ):
             raise ValueError(
@@ -501,7 +519,7 @@ def _normalize_k2_horizon_config(config: PretrainedConfig) -> None:
             target_name="num_dense_layers",
             value=len(mlp_only_layers),
         )
-    elif not is_mova:
+    elif not has_moe_ffn:
         raise ValueError(
             "Dense K2Horizon native loading requires explicit mlp_only_layers"
         )