Add: Support for multiple hidden layers in Eagle3 (#26164)

Signed-off-by: Rahul Tuli <rtuli@redhat.com>

tests/speculative_decoding/speculators/test_eagle3.py

@@ -22,6 +22,10 @@ from vllm.model_executor.models.interfaces import supports_eagle3
             "nm-testing/Speculator-Qwen3-8B-Eagle3-converted-071-quantized-w4a16",
             id="qwen3-eagle3-speculator-w4a16-verifier",
         ),
+        pytest.param(
+            "nm-testing/random-weights-llama3.1.8b-2layer-eagle3",
+            id="llama3-eagl3-multiple-layers",
+        ),
     ],
 )
 def test_eagle3_speculators_model(

vllm/model_executor/models/llama_eagle3.py

@@ -34,15 +34,20 @@ class LlamaDecoderLayer(LlamaDecoderLayer):
         vllm_config: VllmConfig,
         prefix: str = "",
         config: Optional[LlamaConfig] = None,
+        layer_idx: int = 0,
     ) -> None:
         super().__init__(vllm_config, prefix=prefix, config=config)
 
         config = config or vllm_config.model_config.hf_config
         quant_config = self.get_quant_config(vllm_config)
 
+        # First layer uses 2*hidden_size (embeds + hidden_states concatenated)
+        # Subsequent layers use hidden_size (only hidden_states, no embeds)
+        qkv_input_size = 2 * self.hidden_size if layer_idx == 0 else self.hidden_size
+
         # override qkv
         self.self_attn.qkv_proj = QKVParallelLinear(
-            2 * self.hidden_size,
+            qkv_input_size,
             self.self_attn.head_dim,
             self.self_attn.total_num_heads,
             self.self_attn.total_num_kv_heads,
@@ -52,6 +57,7 @@ class LlamaDecoderLayer(LlamaDecoderLayer):
         )
 
         self.hidden_norm = RMSNorm(config.hidden_size, eps=config.rms_norm_eps)
+        self.layer_idx = layer_idx
 
         if getattr(config, "norm_before_residual", False):
             self._residual_norm = self._norm_before_residual
@@ -90,11 +96,15 @@ class LlamaDecoderLayer(LlamaDecoderLayer):
         hidden_states: torch.Tensor,
         residual: Optional[torch.Tensor],
     ) -> tuple[torch.Tensor, torch.Tensor]:
-        embeds = self.input_layernorm(embeds)
+        if self.layer_idx == 0:
+            # First layer: concatenate embeds with hidden_states
+            embeds = self.input_layernorm(embeds)
+            hidden_states, residual = self._residual_norm(hidden_states=hidden_states)
+            hidden_states = torch.cat([embeds, hidden_states], dim=-1)
+        else:
+            # Subsequent layers: process hidden_states and residuals only
+            hidden_states, residual = self.input_layernorm(hidden_states, residual)
 
-        hidden_states, residual = self._residual_norm(hidden_states=hidden_states)
-
-        hidden_states = torch.cat([embeds, hidden_states], dim=-1)
         # Self Attention
         hidden_states = self.self_attn(
             positions=positions,
@@ -133,9 +143,11 @@ class LlamaModel(nn.Module):
             [
                 LlamaDecoderLayer(
                     current_vllm_config,
-                    prefix=maybe_prefix(prefix, f"layers.{start_layer_id}"),
+                    prefix=maybe_prefix(prefix, f"layers.{layer_idx + start_layer_id}"),
                     config=self.config,
+                    layer_idx=layer_idx,
                 )
+                for layer_idx in range(self.config.num_hidden_layers)
             ]
         )
         if hasattr(self.config, "target_hidden_size"):
@@ -166,13 +178,13 @@ class LlamaModel(nn.Module):
         assert hidden_states.shape[-1] == input_embeds.shape[-1]
 
         residual = None
-        hidden_states, residual = self.layers[0](
+        for layer in self.layers:
-            positions,
+            hidden_states, residual = layer(
-            input_embeds,
+                positions=positions,
-            hidden_states,
+                embeds=input_embeds,
-            residual,
+                hidden_states=hidden_states,
-        )
+                residual=residual,
-
+            )
         hidden_states, hidden_prenorm = self.norm(hidden_states, residual)
         return hidden_states, hidden_prenorm