diff --git a/csrc/cpu/pos_encoding.cpp b/csrc/cpu/pos_encoding.cpp
index 8a59e884d6c..74bb014cf39 100644
--- a/csrc/cpu/pos_encoding.cpp
+++ b/csrc/cpu/pos_encoding.cpp
@@ -9,7 +9,8 @@ void rotary_embedding_impl(
     scalar_t* __restrict__ query,           /// [batch_size, seq_len, num_heads,
                                    /// head_size] or [num_tokens, num_heads,
                                    /// head_size]
-    scalar_t* __restrict__ key,  // [batch_size, seq_len, num_kv_heads,
+    scalar_t* __restrict__ key,  // nullptr (optional) or
+                                 // [batch_size, seq_len, num_kv_heads,
                                  // head_size] or [num_tokens, num_kv_heads,
                                  // head_size]
     const scalar_t* __restrict__ cos_sin_cache,  // [max_position, 2, rot_dim //
@@ -85,10 +86,13 @@ void rotary_embedding_impl(
       compute_loop(token_head, cache_ptr, query);
     }
 
-    for (int i = 0; i < num_kv_heads; ++i) {
-      const int head_idx = i;
-      const int64_t token_head = token_idx * key_stride + head_idx * head_size;
-      compute_loop(token_head, cache_ptr, key);
+    if (key != nullptr) {
+      for (int i = 0; i < num_kv_heads; ++i) {
+        const int head_idx = i;
+        const int64_t token_head =
+            token_idx * key_stride + head_idx * head_size;
+        compute_loop(token_head, cache_ptr, key);
+      }
     }
   }
 }
@@ -100,7 +104,8 @@ void rotary_embedding_gptj_impl(
     scalar_t* __restrict__ query,           /// [batch_size, seq_len, num_heads,
                                    /// head_size] or [num_tokens, num_heads,
                                    /// head_size]
-    scalar_t* __restrict__ key,  // [batch_size, seq_len, num_kv_heads,
+    scalar_t* __restrict__ key,  // nullptr (optional) or
+                                 // [batch_size, seq_len, num_kv_heads,
                                  // head_size] or [num_tokens, num_kv_heads,
                                  // head_size]
     const scalar_t* __restrict__ cos_sin_cache,  // [max_position, 2, rot_dim //
@@ -138,6 +143,10 @@ void rotary_embedding_gptj_impl(
     }
   }
 
+  if (key == nullptr) {
+    return;
+  }
+
 #pragma omp parallel for collapse(2)
   for (int token_idx = 0; token_idx < num_tokens; ++token_idx) {
     for (int i = 0; i < num_kv_heads; ++i) {
@@ -168,13 +177,13 @@ void rotary_embedding_gptj_impl(
 };  // namespace
 
 void rotary_embedding(torch::Tensor& positions, torch::Tensor& query,
-                      torch::Tensor& key, int64_t head_size,
+                      std::optional<torch::Tensor> key, int64_t head_size,
                       torch::Tensor& cos_sin_cache, bool is_neox) {
   int num_tokens = positions.numel();
   int rot_dim = cos_sin_cache.size(1);
   int num_heads = query.size(-1) / head_size;
-  int num_kv_heads = key.size(-1) / head_size;
-  int64_t key_stride = key.stride(-2);
+  int num_kv_heads = key.has_value() ? key->size(-1) / head_size : num_heads;
+  int64_t key_stride = key.has_value() ? key->stride(-2) : 0;
   int64_t query_stride = query.stride(-2);
 
   VLLM_DISPATCH_FLOATING_TYPES(
@@ -183,15 +192,15 @@ void rotary_embedding(torch::Tensor& positions, torch::Tensor& query,
         if (is_neox) {
           rotary_embedding_impl(
               positions.data_ptr<int64_t>(), query.data_ptr<scalar_t>(),
-              key.data_ptr<scalar_t>(), cos_sin_cache.data_ptr<scalar_t>(),
-              rot_dim, query_stride, key_stride, num_heads, num_kv_heads,
-              head_size, num_tokens);
+              key.has_value() ? key->data_ptr<scalar_t>() : nullptr,
+              cos_sin_cache.data_ptr<scalar_t>(), rot_dim, query_stride,
+              key_stride, num_heads, num_kv_heads, head_size, num_tokens);
         } else {
           rotary_embedding_gptj_impl(
               positions.data_ptr<int64_t>(), query.data_ptr<scalar_t>(),
-              key.data_ptr<scalar_t>(), cos_sin_cache.data_ptr<scalar_t>(),
-              rot_dim, query_stride, key_stride, num_heads, num_kv_heads,
-              head_size, num_tokens);
+              key.has_value() ? key->data_ptr<scalar_t>() : nullptr,
+              cos_sin_cache.data_ptr<scalar_t>(), rot_dim, query_stride,
+              key_stride, num_heads, num_kv_heads, head_size, num_tokens);
         }
 
         CPU_KERNEL_GUARD_OUT(rotary_embedding_impl)
diff --git a/csrc/cpu/torch_bindings.cpp b/csrc/cpu/torch_bindings.cpp
index 7ae7e3386b4..84b2a8555cc 100644
--- a/csrc/cpu/torch_bindings.cpp
+++ b/csrc/cpu/torch_bindings.cpp
@@ -117,7 +117,7 @@ TORCH_LIBRARY_EXPAND(TORCH_EXTENSION_NAME, ops) {
   // Apply GPT-NeoX or GPT-J style rotary embedding to query and key.
   ops.def(
       "rotary_embedding(Tensor positions, Tensor! query,"
-      "                 Tensor! key, int head_size,"
+      "                 Tensor!? key, int head_size,"
       "                 Tensor cos_sin_cache, bool is_neox) -> ()");
   ops.impl("rotary_embedding", torch::kCPU, &rotary_embedding);
 
diff --git a/csrc/ops.h b/csrc/ops.h
index 59ae0937604..8c4d19963e5 100644
--- a/csrc/ops.h
+++ b/csrc/ops.h
@@ -86,13 +86,13 @@ void rms_norm_dynamic_per_token_quant(torch::Tensor& out,
                                       std::optional<torch::Tensor> residual);
 
 void rotary_embedding(torch::Tensor& positions, torch::Tensor& query,
-                      torch::Tensor& key, int64_t head_size,
+                      std::optional<torch::Tensor> key, int64_t head_size,
                       torch::Tensor& cos_sin_cache, bool is_neox);
 
 void batched_rotary_embedding(torch::Tensor& positions, torch::Tensor& query,
-                              torch::Tensor& key, int64_t head_size,
-                              torch::Tensor& cos_sin_cache, bool is_neox,
-                              int64_t rot_dim,
+                              std::optional<torch::Tensor> key,
+                              int64_t head_size, torch::Tensor& cos_sin_cache,
+                              bool is_neox, int64_t rot_dim,
                               torch::Tensor& cos_sin_cache_offsets);
 
 void silu_and_mul(torch::Tensor& out, torch::Tensor& input);
diff --git a/csrc/pos_encoding_kernels.cu b/csrc/pos_encoding_kernels.cu
index c085d31a3e9..ef6dd1c0978 100644
--- a/csrc/pos_encoding_kernels.cu
+++ b/csrc/pos_encoding_kernels.cu
@@ -38,7 +38,8 @@ inline __device__ void apply_rotary_embedding(
     scalar_t* __restrict__ query,  // [batch_size, seq_len, num_heads,
                                    // head_size] or [num_tokens, num_heads,
                                    // head_size]
-    scalar_t* __restrict__ key,    // [batch_size, seq_len, num_kv_heads,
+    scalar_t* __restrict__ key,    // nullptr or
+                                   // [batch_size, seq_len, num_kv_heads,
                                    // head_size] or [num_tokens, num_kv_heads,
                                    // head_size]
     const scalar_t* cache_ptr, const int head_size, const int num_heads,
@@ -57,13 +58,15 @@ inline __device__ void apply_rotary_embedding(
         query + token_head, cos_ptr, sin_ptr, rot_offset, embed_dim);
   }
 
-  const int nk = num_kv_heads * embed_dim;
-  for (int i = threadIdx.x; i < nk; i += blockDim.x) {
-    const int head_idx = i / embed_dim;
-    const int64_t token_head = token_idx * key_stride + head_idx * head_size;
-    const int rot_offset = i % embed_dim;
-    apply_token_rotary_embedding<scalar_t, IS_NEOX>(
-        key + token_head, cos_ptr, sin_ptr, rot_offset, embed_dim);
+  if (key != nullptr) {
+    const int nk = num_kv_heads * embed_dim;
+    for (int i = threadIdx.x; i < nk; i += blockDim.x) {
+      const int head_idx = i / embed_dim;
+      const int64_t token_head = token_idx * key_stride + head_idx * head_size;
+      const int rot_offset = i % embed_dim;
+      apply_token_rotary_embedding<scalar_t, IS_NEOX>(
+          key + token_head, cos_ptr, sin_ptr, rot_offset, embed_dim);
+    }
   }
 }
 
@@ -74,7 +77,8 @@ __global__ void rotary_embedding_kernel(
     scalar_t* __restrict__ query,           // [batch_size, seq_len, num_heads,
                                    // head_size] or [num_tokens, num_heads,
                                    // head_size]
-    scalar_t* __restrict__ key,  // [batch_size, seq_len, num_kv_heads,
+    scalar_t* __restrict__ key,  // nullptr or
+                                 // [batch_size, seq_len, num_kv_heads,
                                  // head_size] or [num_tokens, num_kv_heads,
                                  // head_size]
     const scalar_t* __restrict__ cos_sin_cache,  // [max_position, 2, rot_dim //
@@ -98,7 +102,8 @@ __global__ void batched_rotary_embedding_kernel(
     scalar_t* __restrict__ query,           // [batch_size, seq_len, num_heads,
                                    // head_size] or [num_tokens, num_heads,
                                    // head_size]
-    scalar_t* __restrict__ key,  // [batch_size, seq_len, num_kv_heads,
+    scalar_t* __restrict__ key,  // nullptr or
+                                 // [batch_size, seq_len, num_kv_heads,
                                  // head_size] or [num_tokens, num_kv_heads,
                                  // head_size]
     const scalar_t* __restrict__ cos_sin_cache,  // [max_position, 2, rot_dim //
@@ -127,10 +132,12 @@ void rotary_embedding(
                            // [num_tokens, num_heads * head_size] or
                            // [batch_size, seq_len, num_heads, head_size] or
                            // [num_tokens, num_heads, head_size]
-    torch::Tensor& key,    // [batch_size, seq_len, num_kv_heads * head_size] or
-                           // [num_tokens, num_kv_heads * head_size] or
-                           // [batch_size, seq_len, num_heads, head_size] or
-                           // [num_tokens, num_heads, head_size]
+    std::optional<torch::Tensor> key,
+    // null or
+    // [batch_size, seq_len, num_kv_heads * head_size] or
+    // [num_tokens, num_kv_heads * head_size] or
+    // [batch_size, seq_len, num_heads, head_size] or
+    // [num_tokens, num_heads, head_size]
     int64_t head_size,
     torch::Tensor& cos_sin_cache,  // [max_position, rot_dim]
     bool is_neox) {
@@ -138,40 +145,40 @@ void rotary_embedding(
   int64_t num_tokens = positions.numel();
   int positions_ndim = positions.dim();
 
-  // Make sure num_tokens dim is consistent across positions, query, and key.
+  // Make sure num_tokens dim is consistent across positions, query, and key
   TORCH_CHECK(
       positions_ndim == 1 || positions_ndim == 2,
       "positions must have shape [num_tokens] or [batch_size, seq_len]");
   if (positions_ndim == 1) {
-    TORCH_CHECK(
-        query.size(0) == positions.size(0) && key.size(0) == positions.size(0),
-        "query, key and positions must have the same number of tokens");
+    TORCH_CHECK(query.size(0) == positions.size(0) &&
+                    (!key.has_value() || key->size(0) == positions.size(0)),
+                "query, key and positions must have the same number of tokens");
   }
   if (positions_ndim == 2) {
     TORCH_CHECK(
         query.size(0) == positions.size(0) &&
-            key.size(0) == positions.size(0) &&
+            (!key.has_value() || key->size(0) == positions.size(0)) &&
             query.size(1) == positions.size(1) &&
-            key.size(1) == positions.size(1),
+            (!key.has_value() || key->size(1) == positions.size(1)),
         "query, key and positions must have the same batch_size and seq_len");
   }
 
   // Make sure head_size is valid for query and key
   // hidden_size = num_heads * head_size
   int query_hidden_size = query.numel() / num_tokens;
-  int key_hidden_size = key.numel() / num_tokens;
+  int key_hidden_size = key.has_value() ? key->numel() / num_tokens : 0;
   TORCH_CHECK(query_hidden_size % head_size == 0);
   TORCH_CHECK(key_hidden_size % head_size == 0);
 
   // Make sure query and key have consistent number of heads
   int num_heads = query_hidden_size / head_size;
-  int num_kv_heads = key_hidden_size / head_size;
+  int num_kv_heads = key.has_value() ? key_hidden_size / head_size : num_heads;
   TORCH_CHECK(num_heads % num_kv_heads == 0);
 
   int rot_dim = cos_sin_cache.size(1);
   int seq_dim_idx = positions_ndim - 1;
   int64_t query_stride = query.stride(seq_dim_idx);
-  int64_t key_stride = key.stride(seq_dim_idx);
+  int64_t key_stride = key.has_value() ? key->stride(seq_dim_idx) : 0;
 
   dim3 grid(num_tokens);
   dim3 block(std::min<int64_t>(num_heads * rot_dim / 2, 512));
@@ -181,15 +188,16 @@ void rotary_embedding(
     if (is_neox) {
       vllm::rotary_embedding_kernel<scalar_t, true><<<grid, block, 0, stream>>>(
           positions.data_ptr<int64_t>(), query.data_ptr<scalar_t>(),
-          key.data_ptr<scalar_t>(), cos_sin_cache.data_ptr<scalar_t>(), rot_dim,
-          query_stride, key_stride, num_heads, num_kv_heads, head_size);
+          key.has_value() ? key->data_ptr<scalar_t>() : nullptr,
+          cos_sin_cache.data_ptr<scalar_t>(), rot_dim, query_stride, key_stride,
+          num_heads, num_kv_heads, head_size);
     } else {
       vllm::rotary_embedding_kernel<scalar_t, false>
           <<<grid, block, 0, stream>>>(
               positions.data_ptr<int64_t>(), query.data_ptr<scalar_t>(),
-              key.data_ptr<scalar_t>(), cos_sin_cache.data_ptr<scalar_t>(),
-              rot_dim, query_stride, key_stride, num_heads, num_kv_heads,
-              head_size);
+              key.has_value() ? key->data_ptr<scalar_t>() : nullptr,
+              cos_sin_cache.data_ptr<scalar_t>(), rot_dim, query_stride,
+              key_stride, num_heads, num_kv_heads, head_size);
     }
   });
 }
@@ -204,10 +212,12 @@ void batched_rotary_embedding(
                            // [num_tokens, num_heads * head_size] or
                            // [batch_size, seq_len, num_heads, head_size] or
                            // [num_tokens, num_heads, head_size]
-    torch::Tensor& key,    // [batch_size, seq_len, num_kv_heads * head_size] or
-                           // [num_tokens, num_kv_heads * head_size] or
-                           // [batch_size, seq_len, num_heads, head_size] or
-                           // [num_tokens, num_heads, head_size]
+    std::optional<torch::Tensor>
+        key,  // null or
+              // [batch_size, seq_len, num_kv_heads * head_size] or
+              // [num_tokens, num_kv_heads * head_size] or
+              // [batch_size, seq_len, num_heads, head_size] or
+              // [num_tokens, num_heads, head_size]
     int64_t head_size,
     torch::Tensor& cos_sin_cache,  // [max_position, rot_dim]
     bool is_neox, int64_t rot_dim,
@@ -221,38 +231,38 @@ void batched_rotary_embedding(
       "cos_sin_cache_offsets");
 
   int positions_ndim = positions.dim();
-  // Make sure num_tokens dim is consistent across positions, query, and key.
+  // Make sure num_tokens dim is consistent across positions, query, and key
   TORCH_CHECK(
       positions_ndim == 1 || positions_ndim == 2,
       "positions must have shape [num_tokens] or [batch_size, seq_len]");
   if (positions_ndim == 1) {
-    TORCH_CHECK(
-        query.size(0) == positions.size(0) && key.size(0) == positions.size(0),
-        "query, key and positions must have the same number of tokens");
+    TORCH_CHECK(query.size(0) == positions.size(0) &&
+                    (!key.has_value() || key->size(0) == positions.size(0)),
+                "query, key and positions must have the same number of tokens");
   }
   if (positions_ndim == 2) {
     TORCH_CHECK(
         query.size(0) == positions.size(0) &&
-            key.size(0) == positions.size(0) &&
+            (!key.has_value() || key->size(0) == positions.size(0)) &&
             query.size(1) == positions.size(1) &&
-            key.size(1) == positions.size(1),
+            (!key.has_value() || key->size(1) == positions.size(1)),
         "query, key and positions must have the same batch_size and seq_len");
   }
 
   // Make sure head_size is valid for query and key
   int query_hidden_size = query.numel() / num_tokens;
-  int key_hidden_size = key.numel() / num_tokens;
+  int key_hidden_size = key.has_value() ? key->numel() / num_tokens : 0;
   TORCH_CHECK(query_hidden_size % head_size == 0);
   TORCH_CHECK(key_hidden_size % head_size == 0);
 
   // Make sure query and key have concistent number of heads
   int num_heads = query_hidden_size / head_size;
-  int num_kv_heads = key_hidden_size / head_size;
+  int num_kv_heads = key.has_value() ? key_hidden_size / head_size : num_heads;
   TORCH_CHECK(num_heads % num_kv_heads == 0);
 
   int seq_dim_idx = positions_ndim - 1;
   int64_t query_stride = query.stride(seq_dim_idx);
-  int64_t key_stride = key.stride(seq_dim_idx);
+  int64_t key_stride = key.has_value() ? key->stride(seq_dim_idx) : 0;
 
   dim3 grid(num_tokens);
   dim3 block(std::min<int64_t>(num_heads * rot_dim / 2, 512));
@@ -263,14 +273,16 @@ void batched_rotary_embedding(
       vllm::batched_rotary_embedding_kernel<scalar_t, true>
           <<<grid, block, 0, stream>>>(
               positions.data_ptr<int64_t>(), query.data_ptr<scalar_t>(),
-              key.data_ptr<scalar_t>(), cos_sin_cache.data_ptr<scalar_t>(),
+              key.has_value() ? key->data_ptr<scalar_t>() : nullptr,
+              cos_sin_cache.data_ptr<scalar_t>(),
               cos_sin_cache_offsets.data_ptr<int64_t>(), rot_dim, query_stride,
               key_stride, num_heads, num_kv_heads, head_size);
     } else {
       vllm::batched_rotary_embedding_kernel<scalar_t, false>
           <<<grid, block, 0, stream>>>(
               positions.data_ptr<int64_t>(), query.data_ptr<scalar_t>(),
-              key.data_ptr<scalar_t>(), cos_sin_cache.data_ptr<scalar_t>(),
+              key.has_value() ? key->data_ptr<scalar_t>() : nullptr,
+              cos_sin_cache.data_ptr<scalar_t>(),
               cos_sin_cache_offsets.data_ptr<int64_t>(), rot_dim, query_stride,
               key_stride, num_heads, num_kv_heads, head_size);
     }
diff --git a/csrc/torch_bindings.cpp b/csrc/torch_bindings.cpp
index f59b42d88c6..f207a4c2fa3 100644
--- a/csrc/torch_bindings.cpp
+++ b/csrc/torch_bindings.cpp
@@ -176,7 +176,7 @@ TORCH_LIBRARY_EXPAND(TORCH_EXTENSION_NAME, ops) {
   // Apply GPT-NeoX or GPT-J style rotary embedding to query and key.
   ops.def(
       "rotary_embedding(Tensor positions, Tensor! query,"
-      "                 Tensor! key, int head_size,"
+      "                 Tensor!? key, int head_size,"
       "                 Tensor cos_sin_cache, bool is_neox) -> ()");
   ops.impl("rotary_embedding", torch::kCUDA, &rotary_embedding);
 
@@ -184,7 +184,7 @@ TORCH_LIBRARY_EXPAND(TORCH_EXTENSION_NAME, ops) {
   // (supports multiple loras).
   ops.def(
       "batched_rotary_embedding(Tensor positions, Tensor! query,"
-      "                         Tensor! key, int head_size,"
+      "                         Tensor!? key, int head_size,"
       "                         Tensor cos_sin_cache, bool is_neox,"
       "                         int rot_dim,"
       "                         Tensor cos_sin_cache_offsets) -> ()");
diff --git a/tests/kernels/core/test_pos_encoding.py b/tests/kernels/core/test_pos_encoding.py
index 2b7bf755ec2..d81c7487b88 100644
--- a/tests/kernels/core/test_pos_encoding.py
+++ b/tests/kernels/core/test_pos_encoding.py
@@ -21,6 +21,7 @@
 CUDA_DEVICES = [
     f"cuda:{i}" for i in range(1 if torch.cuda.device_count() == 1 else 2)
 ]
+USE_KEY = [True, False]
 
 
 def _get_flat_tensor_shape(batch_size: int, seq_len: int, num_heads: int,
@@ -46,6 +47,7 @@ def _get_batch_tensor_shape(batch_size: int, seq_len: int, num_heads: int,
 @pytest.mark.parametrize("dtype", DTYPES)
 @pytest.mark.parametrize("seed", SEEDS)
 @pytest.mark.parametrize("device", CUDA_DEVICES)
+@pytest.mark.parametrize("use_key", USE_KEY)
 @torch.inference_mode()
 def test_rotary_embedding(
     is_neox_style: bool,
@@ -58,6 +60,7 @@ def test_rotary_embedding(
     dtype: torch.dtype,
     seed: int,
     device: str,
+    use_key: bool,
     max_position: int = 8192,
     base: int = 10000,
 ) -> None:
@@ -74,7 +77,7 @@ def test_rotary_embedding(
     positions = torch.randint(0, max_position, (batch_size, seq_len))
     query_shape = tensor_shape_fn(batch_size, seq_len, num_heads, head_size)
     query = torch.randn(query_shape, dtype=dtype)
-    key = torch.randn_like(query)
+    key = torch.randn_like(query) if use_key else None
 
     # NOTE(woosuk): The reference implementation should be executed first
     # because the custom kernel is in-place.
@@ -85,10 +88,14 @@ def test_rotary_embedding(
                                ref_query,
                                atol=get_default_atol(out_query),
                                rtol=get_default_rtol(out_query))
-    torch.testing.assert_close(out_key,
-                               ref_key,
-                               atol=get_default_atol(out_key),
-                               rtol=get_default_rtol(out_key))
+    if use_key:
+        torch.testing.assert_close(out_key,
+                                   ref_key,
+                                   atol=get_default_atol(out_key),
+                                   rtol=get_default_rtol(out_key))
+    else:
+        assert ref_key is None and out_key is None, \
+            "expected returned key to be None"
 
 
 @pytest.mark.parametrize("is_neox_style", IS_NEOX_STYLE)
@@ -101,6 +108,7 @@ def test_rotary_embedding(
 @pytest.mark.parametrize("dtype", DTYPES)
 @pytest.mark.parametrize("seed", SEEDS)
 @pytest.mark.parametrize("device", CUDA_DEVICES)
+@pytest.mark.parametrize("use_key", USE_KEY)
 @torch.inference_mode()
 def test_batched_rotary_embedding(
     is_neox_style: bool,
@@ -113,6 +121,7 @@ def test_batched_rotary_embedding(
     dtype: torch.dtype,
     seed: int,
     device: str,
+    use_key: bool,
     max_position: int = 8192,
     base: int = 10000,
 ) -> None:
@@ -129,7 +138,7 @@ def test_batched_rotary_embedding(
     positions = torch.randint(0, max_position, (batch_size, seq_len))
     query_shape = tensor_shape_fn(batch_size, seq_len, num_heads, head_size)
     query = torch.randn(query_shape, dtype=dtype)
-    key = torch.randn_like(query)
+    key = torch.randn_like(query) if use_key else None
 
     # NOTE(woosuk): The reference implementation should be executed first
     # because the custom kernel is in-place.
@@ -145,10 +154,14 @@ def test_batched_rotary_embedding(
                                ref_query,
                                atol=get_default_atol(out_query),
                                rtol=get_default_rtol(out_query))
-    torch.testing.assert_close(out_key,
-                               ref_key,
-                               atol=get_default_atol(out_key),
-                               rtol=get_default_rtol(out_key))
+    if use_key:
+        torch.testing.assert_close(out_key,
+                                   ref_key,
+                                   atol=get_default_atol(out_key),
+                                   rtol=get_default_rtol(out_key))
+    else:
+        assert ref_key is None and out_key is None, \
+            "expected returned key to be None"
 
 
 @pytest.mark.parametrize("is_neox_style", IS_NEOX_STYLE)
@@ -160,6 +173,7 @@ def test_batched_rotary_embedding(
 @pytest.mark.parametrize("dtype", DTYPES)
 @pytest.mark.parametrize("seed", SEEDS)
 @pytest.mark.parametrize("device", CUDA_DEVICES)
+@pytest.mark.parametrize("use_key", USE_KEY)
 @torch.inference_mode()
 def test_batched_rotary_embedding_multi_lora(
     is_neox_style: bool,
@@ -171,6 +185,7 @@ def test_batched_rotary_embedding_multi_lora(
     dtype: torch.dtype,
     seed: int,
     device: str,
+    use_key: bool,
     max_position: int = 8192,
     base: int = 10000,
 ) -> None:
@@ -190,7 +205,7 @@ def test_batched_rotary_embedding_multi_lora(
                         seq_len,
                         num_heads * head_size,
                         dtype=dtype)
-    key = torch.randn_like(query)
+    key = torch.randn_like(query) if use_key else None
 
     offset_map = torch.tensor(
         list(
@@ -214,10 +229,14 @@ def test_batched_rotary_embedding_multi_lora(
                                ref_query,
                                atol=get_default_atol(out_query),
                                rtol=get_default_rtol(out_query))
-    torch.testing.assert_close(out_key,
-                               ref_key,
-                               atol=get_default_atol(out_key),
-                               rtol=get_default_rtol(out_key))
+    if use_key:
+        torch.testing.assert_close(out_key,
+                                   ref_key,
+                                   atol=get_default_atol(out_key),
+                                   rtol=get_default_rtol(out_key))
+    else:
+        assert ref_key is None and out_key is None, \
+            "expected returned key to be None"
 
 
 @torch.inference_mode()
diff --git a/tests/kernels/core/test_rotary_embedding.py b/tests/kernels/core/test_rotary_embedding.py
index c497dd90edd..4e54861005f 100644
--- a/tests/kernels/core/test_rotary_embedding.py
+++ b/tests/kernels/core/test_rotary_embedding.py
@@ -15,7 +15,7 @@
 def rotary_embedding_opcheck(rot,
                              positions: torch.Tensor,
                              query: torch.Tensor,
-                             key: torch.Tensor,
+                             key: Optional[torch.Tensor] = None,
                              offsets: Optional[torch.Tensor] = None):
     cos_sin_cache = rot.cos_sin_cache.to(query.device, dtype=query.dtype)
 
@@ -37,9 +37,10 @@ def rotary_embedding_opcheck(rot,
 @pytest.mark.parametrize("rotary_dim", [32])
 @pytest.mark.parametrize("head_size", [32, 108])
 @pytest.mark.parametrize("seq_len", [11, 1024])
+@pytest.mark.parametrize("use_key", [True, False])
 def test_rotary_embedding_opcheck(dist_init, device, max_position,
                                   is_neox_style, rotary_dim, head_size,
-                                  seq_len):
+                                  seq_len, use_key):
     batch_size = 1
     base = 10000
     num_heads = 7
@@ -54,7 +55,7 @@ def test_rotary_embedding_opcheck(dist_init, device, max_position,
                         num_heads * head_size,
                         dtype=torch.float32,
                         device=device)
-    key = torch.randn_like(query)
+    key = torch.randn_like(query) if use_key else None
 
     rotary_embedding_opcheck(rot, positions, query, key)
     offsets = torch.zeros(batch_size * seq_len,
diff --git a/tests/neuron/1_core/test_rotary_embedding.py b/tests/neuron/1_core/test_rotary_embedding.py
index c015b80bd47..da57631fcfc 100644
--- a/tests/neuron/1_core/test_rotary_embedding.py
+++ b/tests/neuron/1_core/test_rotary_embedding.py
@@ -11,14 +11,16 @@
 
 
 @pytest.mark.parametrize(
-    "max_position,is_neox_style,rotary_dim,head_size,seq_len", [
-        (16, False, 32, 32, 1024),
-        (16, False, 32, 128, 1024),
-        (16, True, 32, 32, 1024),
-        (16, True, 32, 128, 1024),
+    "max_position,is_neox_style,rotary_dim,head_size,seq_len,use_key", [
+        (16, False, 32, 32, 1024, True),
+        (16, False, 32, 128, 1024, True),
+        (16, True, 32, 32, 1024, True),
+        (16, True, 32, 128, 1024, True),
+        (16, False, 32, 128, 1024, False),
+        (16, True, 32, 128, 1024, False),
     ])
 def test_rotary_embedding_opcheck(max_position, is_neox_style, rotary_dim,
-                                  head_size, seq_len):
+                                  head_size, seq_len, use_key):
     import torch_xla.core.xla_model as xm
 
     device = xm.xla_device()
@@ -40,19 +42,26 @@ def test_rotary_embedding_opcheck(max_position, is_neox_style, rotary_dim,
                         num_heads * head_size,
                         dtype=torch.float32,
                         device="cpu")
-    key = torch.randn_like(query)
-
+    key = torch.randn_like(query) if use_key else None
     assert positions.is_cpu, \
         "reference input tensor is expected to be CPU tensor."
     ref_query, ref_key = rot.to(device="cpu").forward_native(
         positions, query, key)
     out_query, out_key = rot.to(device=device).forward_neuron(
         positions.to(device=device), query.to(device=device),
-        key.to(device=device))
-    assert out_query.is_xla and out_key.is_xla, \
-        "output tensor is expected to be XLA tensor"
+        key.to(device=device) if key is not None else None)
+    if use_key:
+        assert out_query.is_xla and out_key.is_xla, \
+            "output tensor is expected to be XLA tensor"
+        torch.testing.assert_close(out_key.cpu(),
+                                   ref_key,
+                                   atol=1e-2,
+                                   rtol=1e-2)
+    else:
+        assert out_key is None, "expected returned key to be None"
+        assert out_query.is_xla, \
+            "output tensor is expected to be XLA tensor"
     torch.testing.assert_close(out_query.cpu(),
                                ref_query,
                                atol=1e-2,
                                rtol=1e-2)
-    torch.testing.assert_close(out_key.cpu(), ref_key, atol=1e-2, rtol=1e-2)
diff --git a/vllm/_custom_ops.py b/vllm/_custom_ops.py
index 44377ccb295..463cc1a8c64 100644
--- a/vllm/_custom_ops.py
+++ b/vllm/_custom_ops.py
@@ -153,34 +153,36 @@ def merge_attn_states(output: torch.Tensor,
 def rotary_embedding(
     positions: torch.Tensor,
     query: torch.Tensor,
-    key: torch.Tensor,
+    key: Optional[torch.Tensor],
     head_size: int,
     cos_sin_cache: torch.Tensor,
     is_neox: bool,
 ) -> None:
     # TODO: Remove this contiguous call when the kernel is updated to support tensor slices
     query_contiguous = query.contiguous()
-    key_contiguous = key.contiguous()
+    key_contiguous = key.contiguous() if key is not None else None
     torch.ops._C.rotary_embedding(positions, query_contiguous, key_contiguous,
                                   head_size, cos_sin_cache, is_neox)
     query.copy_(query_contiguous)
-    key.copy_(key_contiguous)
+    if key is not None:
+        key.copy_(key_contiguous)
 
 
 def batched_rotary_embedding(positions: torch.Tensor, query: torch.Tensor,
-                             key: torch.Tensor, head_size: int,
+                             key: Optional[torch.Tensor], head_size: int,
                              cos_sin_cache: torch.Tensor, is_neox: bool,
                              rot_dim: int,
                              cos_sin_cache_offsets: torch.Tensor) -> None:
     # TODO: Remove this contiguous call when the kernel is updated to support tensor slices
     query_contiguous = query.contiguous()
-    key_contiguous = key.contiguous()
+    key_contiguous = key.contiguous() if key is not None else None
     torch.ops._C.batched_rotary_embedding(positions, query_contiguous,
                                           key_contiguous, head_size,
                                           cos_sin_cache, is_neox, rot_dim,
                                           cos_sin_cache_offsets)
     query.copy_(query_contiguous)
-    key.copy_(key_contiguous)
+    if key is not None:
+        key.copy_(key_contiguous)
 
 
 # layer norm ops
diff --git a/vllm/model_executor/layers/rotary_embedding.py b/vllm/model_executor/layers/rotary_embedding.py
index 523250c3080..32c2a2859b4 100644
--- a/vllm/model_executor/layers/rotary_embedding.py
+++ b/vllm/model_executor/layers/rotary_embedding.py
@@ -138,9 +138,9 @@ def forward_native(
         self,
         positions: torch.Tensor,
         query: torch.Tensor,
-        key: torch.Tensor,
+        key: Optional[torch.Tensor] = None,
         offsets: Optional[torch.Tensor] = None,
-    ) -> Tuple[torch.Tensor, torch.Tensor]:
+    ) -> Tuple[torch.Tensor, Optional[torch.Tensor]]:
         """A PyTorch-native implementation of forward()."""
         if offsets is not None:
             positions = positions + offsets
@@ -157,22 +157,24 @@ def forward_native(
                                             self.is_neox_style)
         query = torch.cat((query_rot, query_pass), dim=-1).reshape(query_shape)
 
-        key_shape = key.shape
-        key = key.view(num_tokens, -1, self.head_size)
-        key_rot = key[..., :self.rotary_dim]
-        key_pass = key[..., self.rotary_dim:]
-        key_rot = _apply_rotary_emb_torch(key_rot, cos, sin,
-                                          self.is_neox_style)
-        key = torch.cat((key_rot, key_pass), dim=-1).reshape(key_shape)
+        # key may be None in some cases, e.g. cross-layer KV sharing
+        if key is not None:
+            key_shape = key.shape
+            key = key.view(num_tokens, -1, self.head_size)
+            key_rot = key[..., :self.rotary_dim]
+            key_pass = key[..., self.rotary_dim:]
+            key_rot = _apply_rotary_emb_torch(key_rot, cos, sin,
+                                              self.is_neox_style)
+            key = torch.cat((key_rot, key_pass), dim=-1).reshape(key_shape)
         return query, key
 
     def forward_cuda(
         self,
         positions: torch.Tensor,
         query: torch.Tensor,
-        key: torch.Tensor,
+        key: Optional[torch.Tensor] = None,
         offsets: Optional[torch.Tensor] = None,
-    ) -> Tuple[torch.Tensor, torch.Tensor]:
+    ) -> Tuple[torch.Tensor, Optional[torch.Tensor]]:
         from vllm import _custom_ops as ops
 
         # __setattr__ in nn.Module (called by `self.cos_sin_cache = ...`)
@@ -198,32 +200,39 @@ def forward_xpu(
         self,
         positions: torch.Tensor,
         query: torch.Tensor,
-        key: torch.Tensor,
+        key: Optional[torch.Tensor] = None,
         offsets: Optional[torch.Tensor] = None,
-    ) -> Tuple[torch.Tensor, torch.Tensor]:
+    ) -> Tuple[torch.Tensor, Optional[torch.Tensor]]:
         from vllm._ipex_ops import ipex_ops as ops
 
         self.cos_sin_cache = self.cos_sin_cache.to(positions.device,
                                                    dtype=query.dtype)
         # ops.rotary_embedding()/batched_rotary_embedding()
         # are in-place operations that update the query and key tensors.
-        if offsets is not None:
-            ops.batched_rotary_embedding(positions, query, key, self.head_size,
-                                         self.cos_sin_cache,
-                                         self.is_neox_style, self.rotary_dim,
-                                         offsets)
+        if key is None:
+            # XPU kernel doesn't support key=None so fall back to native impl
+            # TODO(sarckk): add support for optional key in
+            # ipex.llm.functional.rotary_embedding_batched
+            return self.forward_native(positions, query, key, offsets)
         else:
-            ops.rotary_embedding(positions, query, key, self.head_size,
-                                 self.cos_sin_cache, self.is_neox_style)
+            if offsets is not None:
+                ops.batched_rotary_embedding(positions, query, key,
+                                             self.head_size,
+                                             self.cos_sin_cache,
+                                             self.is_neox_style,
+                                             self.rotary_dim, offsets)
+            else:
+                ops.rotary_embedding(positions, query, key, self.head_size,
+                                     self.cos_sin_cache, self.is_neox_style)
         return query, key
 
     def forward_hpu(
         self,
         positions: torch.Tensor,
         query: torch.Tensor,
-        key: torch.Tensor,
+        key: Optional[torch.Tensor] = None,
         offsets: Optional[torch.Tensor] = None,
-    ) -> Tuple[torch.Tensor, torch.Tensor]:
+    ) -> Tuple[torch.Tensor, Optional[torch.Tensor]]:
         from habana_frameworks.torch.hpex.kernels import (
             RotaryPosEmbeddingMode, apply_rotary_pos_emb)
         if offsets is not None:
@@ -265,21 +274,23 @@ def forward_hpu(
                                          rope_mode)
         query = torch.cat((query_rot, query_pass), dim=-1).reshape(query_shape)
 
-        key_shape = key.shape
-        key = key.view(num_tokens, -1, self.head_size)
-        key_rot = key[..., :self.rotary_dim]
-        key_pass = key[..., self.rotary_dim:]
-        key_rot = apply_rotary_pos_emb(key_rot, cos, sin, None, 0, rope_mode)
-        key = torch.cat((key_rot, key_pass), dim=-1).reshape(key_shape)
+        if key is not None:
+            key_shape = key.shape
+            key = key.view(num_tokens, -1, self.head_size)
+            key_rot = key[..., :self.rotary_dim]
+            key_pass = key[..., self.rotary_dim:]
+            key_rot = apply_rotary_pos_emb(key_rot, cos, sin, None, 0,
+                                           rope_mode)
+            key = torch.cat((key_rot, key_pass), dim=-1).reshape(key_shape)
         return query, key
 
     def forward_neuron(
         self,
         positions: torch.Tensor,
         query: torch.Tensor,
-        key: torch.Tensor,
+        key: Optional[torch.Tensor] = None,
         offsets: Optional[torch.Tensor] = None,
-    ) -> Tuple[torch.Tensor, torch.Tensor]:
+    ) -> Tuple[torch.Tensor, Optional[torch.Tensor]]:
 
         def _apply_rotary_emb_neuron(
             x: torch.Tensor,
@@ -319,14 +330,16 @@ def _apply_rotary_emb_neuron(
 
         query_shape = query.shape
         query = query.view(num_tokens, -1, self.head_size)
-        key_shape = key.shape
-        key = key.view(num_tokens, -1, self.head_size)
+        if key is not None:
+            key_shape = key.shape
+            key = key.view(num_tokens, -1, self.head_size)
 
         if self.rotary_dim == self.head_size:
             query = _apply_rotary_emb(query, cos, sin, self.is_neox_style)
             query = query.reshape(query_shape)
-            key = _apply_rotary_emb(key, cos, sin, self.is_neox_style)
-            key = key.reshape(key_shape)
+            if key is not None:
+                key = _apply_rotary_emb(key, cos, sin, self.is_neox_style)
+                key = key.reshape(key_shape)
         else:
             head_size = query.shape[-1]
             query_reshaped = query.view(-1, head_size)
@@ -339,14 +352,15 @@ def _apply_rotary_emb_neuron(
             query = torch.cat((query_rot, query_pass),
                               dim=-1).reshape(query_shape)
 
-            key_reshaped = key.view(-1, head_size)
-            key_pass = key_reshaped[:, self.rotary_dim:].view(
-                *key.shape[:-1], head_size - self.rotary_dim)
-            key_rot = key_reshaped[:, :self.rotary_dim].view(
-                *key.shape[:-1], self.rotary_dim)
-            key_rot = _apply_rotary_emb_neuron(key_rot, cos, sin,
-                                               self.is_neox_style)
-            key = torch.cat((key_rot, key_pass), dim=-1).reshape(key_shape)
+            if key is not None:
+                key_reshaped = key.view(-1, head_size)
+                key_pass = key_reshaped[:, self.rotary_dim:].view(
+                    *key.shape[:-1], head_size - self.rotary_dim)
+                key_rot = key_reshaped[:, :self.rotary_dim].view(
+                    *key.shape[:-1], self.rotary_dim)
+                key_rot = _apply_rotary_emb_neuron(key_rot, cos, sin,
+                                                   self.is_neox_style)
+                key = torch.cat((key_rot, key_pass), dim=-1).reshape(key_shape)
         return query, key
 
     def extra_repr(self) -> str:
@@ -672,9 +686,10 @@ def forward(
         self,
         positions: torch.Tensor,
         query: torch.Tensor,
-        key: torch.Tensor,
+        key: Optional[torch.Tensor] = None,
         offsets: Optional[torch.Tensor] = None,
-    ) -> Tuple[torch.Tensor, torch.Tensor]:
+    ) -> Tuple[torch.Tensor, Optional[torch.Tensor]]:
+        assert key is not None
         query = query.view(*query.shape[:-1], -1, self.head_size)
         key = key.view(*key.shape[:-1], -1, self.head_size)
 
@@ -782,10 +797,11 @@ def forward(
         self,
         positions: torch.Tensor,
         query: torch.Tensor,
-        key: torch.Tensor,
+        key: Optional[torch.Tensor] = None,
         offsets: Optional[torch.Tensor] = None,
-    ) -> Tuple[torch.Tensor, torch.Tensor]:
+    ) -> Tuple[torch.Tensor, Optional[torch.Tensor]]:
         """PyTorch-native implementation equivalent to forward()."""
+        assert key is not None
         query_rot = query[..., :self.rotary_dim]
         key_rot = key[..., :self.rotary_dim]
         if self.rotary_dim < self.head_size:
@@ -912,8 +928,9 @@ def _compute_cos_sin_cache(self) -> torch.Tensor:
     def forward(
         self,
         query: torch.Tensor,
-        key: torch.Tensor,
-    ) -> Tuple[torch.Tensor, torch.Tensor]:
+        key: Optional[torch.Tensor] = None,
+    ) -> Tuple[torch.Tensor, Optional[torch.Tensor]]:
+        assert key is not None
         self.cos_sin_cache: torch.Tensor = self.cos_sin_cache.to(query.device)
         query_ = torch.view_as_complex(query.float().reshape(
             *query.shape[:-1], -1, 2))
@@ -957,8 +974,8 @@ def forward(
         self,
         positions: torch.Tensor,
         query: torch.Tensor,
-        key: torch.Tensor,
-    ) -> Tuple[torch.Tensor, torch.Tensor]:
+        key: Optional[torch.Tensor] = None,
+    ) -> Tuple[torch.Tensor, Optional[torch.Tensor]]:
         """PyTorch-native implementation equivalent to forward().
 
         Args:
@@ -969,6 +986,7 @@ def forward(
             key: [num_tokens, num_kv_heads * head_size]
         """
         assert positions.ndim == 1 or positions.ndim == 2
+        assert key is not None
 
         num_tokens = positions.shape[-1]
         cos_sin = self.cos_sin_cache[positions]