diff --git a/.buildkite/test-pipeline.yaml b/.buildkite/test-pipeline.yaml
index a020b0d276be..f823ddd128dd 100644
--- a/.buildkite/test-pipeline.yaml
+++ b/.buildkite/test-pipeline.yaml
@@ -347,8 +347,7 @@ steps:
     - vllm/v1/attention
     - tests/v1/attention
   commands:
-    - export VLLM_DISABLE_FLASHINFER_PREFILL=1 # TODO: FI prefill is bugged and causes incorrectness, fix this
-    - pytest -v -s v1/attention
+    - VLLM_DISABLE_FLASHINFER_PREFILL=1 pytest -v -s v1/attention # TODO: FI prefill is bugged and causes incorrectness, fix this
 
 - label: V1 Test others (CPU) # 5 mins
   source_file_dependencies:
diff --git a/tests/v1/attention/test_attention_backends.py b/tests/v1/attention/test_attention_backends.py
index 6659b3eb1e98..08aeb6f298f6 100644
--- a/tests/v1/attention/test_attention_backends.py
+++ b/tests/v1/attention/test_attention_backends.py
@@ -295,6 +295,7 @@ def _test_backend_correctness(
     block_size: int = 16,
     atol: float = 1e-2,
     rtol: float = 1e-2,
+    tensor_parallel_size: int = 1,
 ):
     """
     Test that all backends produce similar outputs to a reference implementation
@@ -310,13 +311,38 @@ def _test_backend_correctness(
     4. Running each vLLM attention backend with the new queries and the
        simulated paged KV cache.
     5. Comparing the vLLM backend's output to the ground-truth SDPA output.
+
+    Note: When tensor_parallel_size > 1, we simulate the head partitioning
+    by overriding the model config to use fewer heads, without requiring
+    multiple GPUs. This tests that backends work correctly with different
+    head counts.
     """
     current_platform.seed_everything(42)
+
+    hf_config_override = None
+    if tensor_parallel_size > 1:
+        from vllm.config import ModelConfig
+
+        temp_config = ModelConfig(model=model, max_model_len=1)
+        original_num_heads = temp_config.hf_text_config.num_attention_heads
+        original_num_kv_heads = getattr(
+            temp_config.hf_text_config, "num_key_value_heads", None
+        )
+        hf_config_override = {
+            "num_attention_heads": original_num_heads // tensor_parallel_size,
+        }
+        if original_num_kv_heads is not None:
+            hf_config_override["num_key_value_heads"] = max(
+                1, original_num_kv_heads // tensor_parallel_size
+            )
+
     vllm_config = create_vllm_config(
         model_name=model,
+        tensor_parallel_size=1,  # Always use TP=1 to avoid multi-GPU requirements
         max_model_len=max(batch_spec.seq_lens),
         block_size=block_size,
         num_gpu_blocks=8192,
+        hf_config_override=hf_config_override,
     )
     device = torch.device("cuda:0")
 
@@ -503,7 +529,10 @@ def error_msg(msg: str, backend_name: str):
     ],
 )
 @pytest.mark.parametrize("model", ["meta-llama/Meta-Llama-3-8B"])
-def test_causal_backend_correctness(batch_spec_name: str, model: str):
+@pytest.mark.parametrize("tensor_parallel_size", [1, 2, 4])
+def test_causal_backend_correctness(
+    batch_spec_name: str, model: str, tensor_parallel_size: int
+):
     """Test backend's correctness with causal attention."""
 
     def causal_mask_mod(
@@ -523,12 +552,23 @@ def causal_mask_mod(
     SMALL_BLOCK_BACKENDS = [
         x for x in BACKENDS_TO_TEST if x not in LARGE_BLOCK_BACKENDS
     ]
-    _test_backend_correctness(batch_spec, model, SMALL_BLOCK_BACKENDS, causal_mask_mod)
+    _test_backend_correctness(
+        batch_spec,
+        model,
+        SMALL_BLOCK_BACKENDS,
+        causal_mask_mod,
+        tensor_parallel_size=tensor_parallel_size,
+    )
 
     # Fast FlexAttention needs to run with block_size=128
     if LARGE_BLOCK_BACKENDS:
         _test_backend_correctness(
-            batch_spec, model, LARGE_BLOCK_BACKENDS, causal_mask_mod, block_size=128
+            batch_spec,
+            model,
+            LARGE_BLOCK_BACKENDS,
+            causal_mask_mod,
+            block_size=128,
+            tensor_parallel_size=tensor_parallel_size,
         )
 
 
@@ -545,7 +585,10 @@ def causal_mask_mod(
     ["small_decode", "small_prefill", "mixed_medium", "large_decode", "large_prefill"],
 )
 @pytest.mark.parametrize("model", ["microsoft/Phi-tiny-MoE-instruct"])
-def test_sliding_window_backend_correctness(batch_spec_name: str, model: str):
+@pytest.mark.parametrize("tensor_parallel_size", [1, 2, 4])
+def test_sliding_window_backend_correctness(
+    batch_spec_name: str, model: str, tensor_parallel_size: int
+):
     """Test backend's correctness with sliding window attention."""
 
     def sliding_window_mask_mod(
@@ -575,7 +618,11 @@ def sliding_window_mask_mod(
         x for x in SLIDING_WINDOW_BACKENDS_TO_TEST if x not in LARGE_BLOCK_BACKENDS
     ]
     _test_backend_correctness(
-        batch_spec, model, SMALL_BLOCK_BACKENDS, sliding_window_mask_mod_fn
+        batch_spec,
+        model,
+        SMALL_BLOCK_BACKENDS,
+        sliding_window_mask_mod_fn,
+        tensor_parallel_size=tensor_parallel_size,
     )
 
     # Fast FlexAttention needs to run with block_size=128
@@ -586,4 +633,5 @@ def sliding_window_mask_mod(
             LARGE_BLOCK_BACKENDS,
             sliding_window_mask_mod_fn,
             block_size=128,
+            tensor_parallel_size=tensor_parallel_size,
         )
diff --git a/tests/v1/attention/test_mla_backends.py b/tests/v1/attention/test_mla_backends.py
index cda4fb11c096..5679fafe63ee 100644
--- a/tests/v1/attention/test_mla_backends.py
+++ b/tests/v1/attention/test_mla_backends.py
@@ -394,8 +394,11 @@ def run_attention_backend(
         "spec_decode_medium",
     ],
 )
-@pytest.mark.parametrize("model", ["deepseek-ai/DeepSeek-V2-Lite-Chat"])
-def test_backend_correctness(dist_init, batch_spec_name: str, model: str):
+@pytest.mark.parametrize("model", ["deepseek-ai/DeepSeek-R1"])
+@pytest.mark.parametrize("tensor_parallel_size", [1, 4, 8, 16])
+def test_backend_correctness(
+    dist_init, batch_spec_name: str, model: str, tensor_parallel_size: int
+):
     """
     Test that all backends produce similar outputs to a reference implementation
     using torch.nn.functional.scaled_dot_product_attention.
@@ -410,6 +413,11 @@ def test_backend_correctness(dist_init, batch_spec_name: str, model: str):
     4. Running each vLLM attention backend with the new queries and the
        simulated paged KV cache.
     5. Comparing the vLLM backend's output to the ground-truth SDPA output.
+
+    Note: When tensor_parallel_size > 1, we simulate the head partitioning
+    by overriding the model config to use fewer heads, without requiring
+    multiple GPUs. This tests that backends work correctly with different
+    head counts.
     """
 
     batch_spec = BATCH_SPECS[batch_spec_name]
@@ -423,11 +431,30 @@ def test_backend_correctness(dist_init, batch_spec_name: str, model: str):
     # Add 1 for null block at index 0, and some buffer
     num_gpu_blocks = required_blocks + 1 + 100
 
+    hf_config_override = None
+    if tensor_parallel_size > 1:
+        from vllm.config import ModelConfig
+
+        temp_config = ModelConfig(model=model, max_model_len=1)
+        original_num_heads = temp_config.hf_text_config.num_attention_heads
+        original_num_kv_heads = getattr(
+            temp_config.hf_text_config, "num_key_value_heads", None
+        )
+        hf_config_override = {
+            "num_attention_heads": original_num_heads // tensor_parallel_size,
+        }
+        if original_num_kv_heads is not None:
+            hf_config_override["num_key_value_heads"] = max(
+                1, original_num_kv_heads // tensor_parallel_size
+            )
+
     vllm_config = create_vllm_config(
         model_name=model,
+        tensor_parallel_size=1,  # Always use TP=1 to avoid multi-GPU requirements
         max_model_len=max(batch_spec.seq_lens),
         num_gpu_blocks=num_gpu_blocks,
         block_size=default_block_size,
+        hf_config_override=hf_config_override,
     )
 
     # For spec decode tests, add a speculative_config to set the reorder_batch_threshold
diff --git a/tests/v1/attention/test_sparse_mla_backends.py b/tests/v1/attention/test_sparse_mla_backends.py
index 02324d2aca6e..b34d587eb362 100644
--- a/tests/v1/attention/test_sparse_mla_backends.py
+++ b/tests/v1/attention/test_sparse_mla_backends.py
@@ -113,7 +113,10 @@ def _quantize_dequantize_fp8_ds_mla(
 
 @pytest.mark.parametrize("batch_name", list(SPARSE_BACKEND_BATCH_SPECS.keys()))
 @pytest.mark.parametrize("kv_cache_dtype", ["fp8_ds_mla", "auto"])
-def test_sparse_backend_decode_correctness(dist_init, batch_name, kv_cache_dtype):
+@pytest.mark.parametrize("tensor_parallel_size", [1, 2, 4])
+def test_sparse_backend_decode_correctness(
+    dist_init, batch_name, kv_cache_dtype, tensor_parallel_size
+):
     if not torch.cuda.is_available():
         pytest.skip("CUDA is required for sparse MLA decode test")
 
@@ -135,8 +138,11 @@ def test_sparse_backend_decode_correctness(dist_init, batch_name, kv_cache_dtype
     total_cache_tokens = sum(batch_spec.seq_lens)
     block_size = 64
 
+    # Note: We use TP=1 to avoid multi-GPU requirements in CI.
+    # The test simulates head partitioning via mocked methods below.
     vllm_config = create_vllm_config(
         model_name="deepseek-ai/DeepSeek-V2-Lite-Chat",
+        tensor_parallel_size=1,
         max_model_len=max_seqlen,
         num_gpu_blocks=max(2048, cdiv(total_cache_tokens, block_size) + 1),
         block_size=block_size,
@@ -156,7 +162,8 @@ def test_sparse_backend_decode_correctness(dist_init, batch_name, kv_cache_dtype
     )
     model_config.dtype = dtype
     model_config.get_num_attention_heads = MethodType(
-        lambda self, parallel_config: num_heads, model_config
+        lambda self, parallel_config: max(1, num_heads // tensor_parallel_size),
+        model_config,
     )
     model_config.get_num_kv_heads = MethodType(
         lambda self, parallel_config: 1, model_config