[Attention Backend] TurboQuant: 2-bit KV cache compression with 4x capacity (#38479)

Signed-off-by: vibhavagarwal5 <vibhavagarwal5@gmail.com>
Signed-off-by: Michael Goin <mgoin64@gmail.com>
Co-authored-by: Xinyu Chen <xinyu1.chen@intel.com>
Co-authored-by: Michael Goin <mgoin64@gmail.com>

.buildkite/test_areas/lm_eval.yaml

@@ -91,6 +91,16 @@ steps:
     - pytest -s -v evals/gsm8k/test_gsm8k_correctness.py --config-list-file=evals/gsm8k/configs/moe-refactor-dp-ep/config-b200.txt
 
 
+- label: LM Eval TurboQuant KV Cache
+  timeout_in_minutes: 75
+  source_file_dependencies:
+  - vllm/model_executor/layers/quantization/turboquant/
+  - vllm/v1/attention/backends/turboquant_attn.py
+  - vllm/v1/attention/ops/triton_turboquant_decode.py
+  - vllm/v1/attention/ops/triton_turboquant_store.py
+  commands:
+  - pytest -s -v evals/gsm8k/test_gsm8k_correctness.py --config-list-file=evals/gsm8k/configs/models-turboquant.txt
+
 - label: GPQA Eval (GPT-OSS) (H100)
   timeout_in_minutes: 120
   device: h100

docs/design/attention_backends.md

@@ -178,6 +178,7 @@ Priority is **1 = highest** (tried first).
 | `ROCM_ATTN` | | fp16, bf16, fp32 | `auto`, `float16`, `bfloat16`, `fp8`, `fp8_e4m3`, `fp8_e5m2` | %16 | 32, 64, 80, 96, 128, 160, 192, 224, 256 | ❌ | ✅ | ❌ | Decoder, Encoder, Encoder Only | N/A |
 | `TREE_ATTN` | | fp16, bf16 | `auto`, `float16`, `bfloat16` | %16 | 32, 64, 96, 128, 160, 192, 224, 256 | ❌ | ❌ | ❌ | Decoder | Any |
 | `TRITON_ATTN` | | fp16, bf16, fp32 | `auto`, `float16`, `bfloat16`, `fp8`, `fp8_e4m3`, `fp8_e5m2`, `int8_per_token_head`, `fp8_per_token_head` | %16 | Any | ✅ | ✅ | ❌ | All | Any |
+| `TURBOQUANT` | | fp16, bf16 | `turboquant_k8v4`, `turboquant_4bit_nc`, `turboquant_k3v4_nc`, `turboquant_3bit_nc` | 16, 32, 64, 128 | Any | ❌ | ❌ | ❌ | Decoder | Any |
 
 > **†** FlashInfer uses TRTLLM attention on Blackwell (SM100), which supports sinks. Disable via `--attention-config.use_trtllm_attention=0`.
 >

pyproject.toml

@@ -170,6 +170,9 @@ eles = "eles"
 datas = "datas"
 ser = "ser"
 ure = "ure"
+# Walsh-Hadamard Transform
+wht = "wht"
+WHT = "WHT"
 
 [tool.uv]
 no-build-isolation-package = ["torch"]

tests/evals/gsm8k/configs/Qwen3-4B-TQ-k3v4nc.yaml

+model_name: "Qwen/Qwen3-4B"
+accuracy_threshold: 0.78
+num_questions: 1319
+num_fewshot: 5
+server_args: "--kv-cache-dtype turboquant_k3v4_nc --enforce-eager --max-model-len 4096"

tests/evals/gsm8k/configs/Qwen3-4B-TQ-k8v4.yaml

+model_name: "Qwen/Qwen3-4B"
+accuracy_threshold: 0.80
+num_questions: 1319
+num_fewshot: 5
+server_args: "--kv-cache-dtype turboquant_k8v4 --enforce-eager --max-model-len 4096"

tests/evals/gsm8k/configs/Qwen3-4B-TQ-t3nc.yaml

+model_name: "Qwen/Qwen3-4B"
+accuracy_threshold: 0.75
+num_questions: 1319
+num_fewshot: 5
+server_args: "--kv-cache-dtype turboquant_3bit_nc --enforce-eager --max-model-len 4096"

tests/evals/gsm8k/configs/Qwen3-4B-TQ-t4nc.yaml

+model_name: "Qwen/Qwen3-4B"
+accuracy_threshold: 0.80
+num_questions: 1319
+num_fewshot: 5
+server_args: "--kv-cache-dtype turboquant_4bit_nc --enforce-eager --max-model-len 4096"

tests/evals/gsm8k/configs/models-turboquant.txt

+Qwen3-4B-TQ-k8v4.yaml
+Qwen3-4B-TQ-t4nc.yaml
+Qwen3-4B-TQ-k3v4nc.yaml
+Qwen3-4B-TQ-t3nc.yaml

vllm/config/attention.py

@@ -27,6 +27,11 @@ class AttentionConfig:
     flash_attn_max_num_splits_for_cuda_graph: int = 32
     """Flash Attention max number splits for cuda graph decode."""
 
+    tq_max_kv_splits_for_cuda_graph: int = 32
+    """TurboQuant max NUM_KV_SPLITS for cuda graph decode.
+    Fixes the split count so grid dimensions are constant across captures,
+    and buffers can be pre-allocated to avoid inflating the memory estimate."""
+
     use_cudnn_prefill: bool = False
     """Whether to use cudnn prefill."""
 

vllm/config/cache.py

@@ -24,6 +24,10 @@ CacheDType = Literal[
     "fp8_e5m2",
     "fp8_inc",
     "fp8_ds_mla",
+    "turboquant_k8v4",
+    "turboquant_4bit_nc",
+    "turboquant_k3v4_nc",
+    "turboquant_3bit_nc",
     "int8_per_token_head",
     "fp8_per_token_head",
 ]

vllm/engine/arg_utils.py

@@ -1642,6 +1642,31 @@ class EngineArgs:
             kv_offloading_backend=self.kv_offloading_backend,
         )
 
+        # TurboQuant: auto-skip first/last 2 layers (boundary protection).
+        # These layers are most sensitive to quantization error.
+        # Users can add extra layers via --kv-cache-dtype-skip-layers.
+        if resolved_cache_dtype.startswith("turboquant_"):
+            if model_config.is_hybrid:
+                raise NotImplementedError(
+                    "TurboQuant KV cache is not supported for hybrid "
+                    "(attention + Mamba) models. Boundary layer protection "
+                    "requires uniform attention layers."
+                )
+            from vllm.model_executor.layers.quantization.turboquant.config import (
+                TurboQuantConfig,
+            )
+
+            num_layers = model_config.hf_text_config.num_hidden_layers
+            boundary = TurboQuantConfig.get_boundary_skip_layers(num_layers)
+            existing = set(cache_config.kv_cache_dtype_skip_layers)
+            merged = sorted(existing | set(boundary), key=lambda x: int(x))
+            cache_config.kv_cache_dtype_skip_layers = merged
+            logger.info(
+                "TQ: skipping layers %s for boundary protection (num_layers=%d)",
+                merged,
+                num_layers,
+            )
+
         ray_runtime_env = None
         if is_ray_initialized():
             # Ray Serve LLM calls `create_engine_config` in the context
@@ -1948,6 +1973,19 @@ class EngineArgs:
                 self.attention_backend
             )
 
+        # TurboQuant requires FlashAttention 2 — FA3 boundary layers assert
+        # FlashAttentionImpl which fails with TurboQuantAttentionImpl.
+        if resolved_cache_dtype.startswith("turboquant_") and (
+            attention_config.flash_attn_version is None
+            or attention_config.flash_attn_version >= 3
+        ):
+            logger.warning(
+                "TurboQuant is not yet compatible with FlashAttention >= 3. "
+                "Overriding flash_attn_version to 2. To silence this "
+                "warning, pass --attention-config.flash_attn_version=2"
+            )
+            attention_config.flash_attn_version = 2
+
         # Mamba config overrides
         mamba_config = copy.deepcopy(self.mamba_config)
         # Convert string to enum if needed (CLI parsing returns a string)

vllm/model_executor/layers/attention/attention.py

@@ -379,6 +379,10 @@ class Attention(nn.Module, AttentionLayerBase):
         # Initialize KV cache quantization attributes
         _init_kv_cache_quant(self, quant_config, prefix)
 
+        # Initialize TurboQuant buffers (Pi, S, centroids) if tq cache dtype
+        if kv_cache_dtype.startswith("turboquant_"):
+            self._init_turboquant_buffers(kv_cache_dtype, head_size, prefix)
+
         # for attn backends supporting query quantization
         self.query_quant = None
         if (
@@ -397,6 +401,67 @@ class Attention(nn.Module, AttentionLayerBase):
                 else GroupShape.PER_TENSOR,
             )
 
+    def _init_turboquant_buffers(
+        self, cache_dtype: str, head_size: int, prefix: str
+    ) -> None:
+        """Initialize TurboQuant rotation/projection matrices and centroids."""
+        from vllm.model_executor.layers.quantization.turboquant.centroids import (
+            get_centroids,
+        )
+        from vllm.model_executor.layers.quantization.turboquant.config import (
+            TurboQuantConfig,
+        )
+        from vllm.model_executor.layers.quantization.turboquant.quantizer import (
+            generate_wht_signs,
+        )
+
+        tq_config = TurboQuantConfig.from_cache_dtype(cache_dtype, head_size)
+
+        # Each layer needs a unique rotation matrix so quantization errors
+        # don't correlate across layers. Stride must exceed max head_dim to
+        # ensure non-overlapping RNG streams between adjacent layers.
+        _TQ_LAYER_SEED_STRIDE = 1337
+
+        from vllm.model_executor.models.utils import extract_layer_index
+
+        layer_idx = extract_layer_index(prefix)
+        seed = tq_config.seed + layer_idx * _TQ_LAYER_SEED_STRIDE
+
+        self.register_buffer(
+            "_tq_signs",
+            generate_wht_signs(head_size, seed=seed),
+        )
+        self.register_buffer(
+            "_tq_centroids",
+            get_centroids(head_size, tq_config.centroid_bits),
+        )
+        self._tq_config = tq_config
+
+        # Pre-allocate decode intermediate buffers so model.to(device) moves
+        # them to GPU *before* the memory profiler runs.  Without this the
+        # profiler gives all free memory to KV cache blocks and the first
+        # decode OOMs when these buffers are lazily allocated.
+        _vllm_cfg = get_current_vllm_config()
+        B = _vllm_cfg.scheduler_config.max_num_seqs
+        Hq = self.num_heads
+        S = _vllm_cfg.attention_config.tq_max_kv_splits_for_cuda_graph
+        D = head_size
+        self.register_buffer(
+            "_tq_mid_o_buf",
+            torch.empty(B, Hq, S, D + 1, dtype=torch.float32),
+            persistent=False,
+        )
+        self.register_buffer(
+            "_tq_output_buf",
+            torch.empty(B, Hq, D, dtype=torch.float32),
+            persistent=False,
+        )
+        self.register_buffer(
+            "_tq_lse_buf",
+            torch.empty(B, Hq, dtype=torch.float32),
+            persistent=False,
+        )
+
     def forward(
         self,
         query: torch.Tensor,
@@ -544,6 +609,23 @@ class Attention(nn.Module, AttentionLayerBase):
                 kv_quant_mode=quant_mode,
                 sliding_window=self.sliding_window,
             )
+        elif self.kv_cache_dtype.startswith("turboquant_"):
+            from vllm.model_executor.layers.quantization.turboquant.config import (
+                TurboQuantConfig,
+            )
+            from vllm.v1.kv_cache_interface import TQFullAttentionSpec
+
+            tq_config = TurboQuantConfig.from_cache_dtype(
+                self.kv_cache_dtype, self.head_size
+            )
+            return TQFullAttentionSpec(
+                block_size=block_size,
+                num_kv_heads=self.num_kv_heads,
+                head_size=self.head_size,
+                head_size_v=self.head_size,
+                dtype=self.kv_cache_torch_dtype,
+                tq_slot_size=tq_config.slot_size_aligned,
+            )
         else:
             return FullAttentionSpec(
                 block_size=block_size,

vllm/model_executor/layers/quantization/turboquant/__init__.py

+# SPDX-License-Identifier: Apache-2.0
+# SPDX-FileCopyrightText: Copyright contributors to the vLLM project
+"""TurboQuant: Near-optimal KV-cache quantization for vLLM.
+
+PolarQuant compression: random rotation + per-coordinate Lloyd-Max
+scalar quantization for keys, uniform quantization for values.
+
+Reference: "TurboQuant: Online Vector Quantization with Near-optimal
+Distortion Rate" (ICLR 2026), Zandieh et al.
+"""
+
+from vllm.model_executor.layers.quantization.turboquant.config import TurboQuantConfig
+
+__all__ = ["TurboQuantConfig"]

vllm/model_executor/layers/quantization/turboquant/centroids.py

+# SPDX-License-Identifier: Apache-2.0
+# SPDX-FileCopyrightText: Copyright contributors to the vLLM project
+"""Lloyd-Max optimal scalar quantizer for TurboQuant.
+
+After rotating a d-dimensional unit vector by a random orthogonal matrix,
+each coordinate approximately follows N(0, 1/d) for d >= 64.
+We solve the Lloyd-Max conditions to find optimal centroids.
+
+Based on: turboquant-pytorch/lloyd_max.py (Zandieh et al.)
+"""
+
+import math
+from functools import lru_cache
+
+import torch
+
+
+def _gaussian_pdf(x: float, sigma2: float) -> float:
+    return (1.0 / math.sqrt(2 * math.pi * sigma2)) * math.exp(-x * x / (2 * sigma2))
+
+
+def _trapz(f, a: float, b: float, n: int = 200) -> float:
+    """Trapezoidal numerical integration (replaces scipy.integrate.quad)."""
+    h = (b - a) / n
+    result = 0.5 * (f(a) + f(b))
+    for i in range(1, n):
+        result += f(a + i * h)
+    return result * h
+
+
+def solve_lloyd_max(
+    d: int,
+    bits: int,
+    max_iter: int = 200,
+    tol: float = 1e-10,
+) -> tuple[torch.Tensor, torch.Tensor]:
+    """Solve Lloyd-Max optimal quantizer for N(0, 1/d) distribution.
+
+    Args:
+        d: Vector dimension (determines variance = 1/d).
+        bits: Number of quantization bits.
+        max_iter: Maximum Lloyd-Max iterations.
+        tol: Convergence tolerance.
+
+    Returns:
+        centroids: Sorted tensor of 2^bits optimal centroids.
+        boundaries: Sorted tensor of 2^bits - 1 decision boundaries.
+    """
+    n_levels = 2**bits
+    sigma2 = 1.0 / d
+    sigma = math.sqrt(sigma2)
+
+    def pdf(x):
+        return _gaussian_pdf(x, sigma2)
+
+    lo, hi = -3.5 * sigma, 3.5 * sigma
+    centroids = [lo + (hi - lo) * (i + 0.5) / n_levels for i in range(n_levels)]
+
+    for _ in range(max_iter):
+        boundaries = [
+            (centroids[i] + centroids[i + 1]) / 2.0 for i in range(n_levels - 1)
+        ]
+        edges = [lo * 3] + boundaries + [hi * 3]
+        new_centroids = []
+        for i in range(n_levels):
+            a, b = edges[i], edges[i + 1]
+            num = _trapz(lambda x: x * pdf(x), a, b)
+            den = _trapz(pdf, a, b)
+            new_centroids.append(num / den if den > 1e-15 else centroids[i])
+
+        if max(abs(new_centroids[i] - centroids[i]) for i in range(n_levels)) < tol:
+            break
+        centroids = new_centroids
+
+    boundaries = [(centroids[i] + centroids[i + 1]) / 2.0 for i in range(n_levels - 1)]
+    return (
+        torch.tensor(centroids, dtype=torch.float32),
+        torch.tensor(boundaries, dtype=torch.float32),
+    )
+
+
+@lru_cache(maxsize=32)
+def get_centroids(d: int, bits: int) -> torch.Tensor:
+    """Get precomputed Lloyd-Max centroids (cached)."""
+    centroids, _ = solve_lloyd_max(d, bits)
+    return centroids

vllm/model_executor/layers/quantization/turboquant/config.py

+# SPDX-License-Identifier: Apache-2.0
+# SPDX-FileCopyrightText: Copyright contributors to the vLLM project
+"""TurboQuant configuration."""
+
+import math
+from dataclasses import dataclass
+
+# Named TQ presets: each maps to frozen config parameters.
+# key_quant_bits: 8 = FP8 keys, 3-4 = MSE (Lloyd-Max) quantized keys.
+# value_quant_bits: 3-4 = uniform quantized values.
+TQ_PRESETS: dict[str, dict] = {
+    "turboquant_k8v4": {
+        "key_quant_bits": 8,
+        "value_quant_bits": 4,
+        "norm_correction": False,
+    },
+    "turboquant_4bit_nc": {
+        "key_quant_bits": 4,
+        "value_quant_bits": 4,
+        "norm_correction": True,
+    },
+    "turboquant_k3v4_nc": {
+        "key_quant_bits": 3,
+        "value_quant_bits": 4,
+        "norm_correction": True,
+    },
+    "turboquant_3bit_nc": {
+        "key_quant_bits": 3,
+        "value_quant_bits": 3,
+        "norm_correction": True,
+    },
+}
+
+
+@dataclass
+class TurboQuantConfig:
+    """Configuration for TurboQuant KV-cache quantization.
+
+    Uses PolarQuant (WHT rotation + Lloyd-Max scalar quantization) for keys
+    and uniform quantization for values. QJL is intentionally omitted —
+    community consensus (5+ independent groups) found it hurts attention
+    quality by amplifying variance through softmax.
+
+    Named presets (use via --kv-cache-dtype):
+        turboquant_k8v4:   FP8 keys + 4-bit values, 2.6x, +1.17% PPL
+        turboquant_4bit_nc: 4-bit MSE keys + 4-bit values + NC, 3.8x, +2.71%
+        turboquant_k3v4_nc: 3-bit MSE keys + 4-bit values + NC, ~3.5x, +10.63%
+        turboquant_3bit_nc: 3-bit MSE keys + 3-bit values + NC, 4.9x, +20.59%
+
+    Args:
+        head_dim: Attention head dimension (e.g. 64, 96, 128).
+        key_quant_bits: Bits for key quantization. 8 = FP8 keys (no
+            rotation/MSE). 3-4 = Lloyd-Max MSE quantized keys.
+        value_quant_bits: Bits per value dimension for uniform quantization.
+            3 = 8 levels, 4 = 16 levels (default).
+        seed: Base seed for deterministic random matrix generation.
+            Actual seed per layer = seed + layer_idx * 1337.
+        norm_correction: Re-normalize centroid vectors to unit norm before
+            inverse rotation during dequant. Fixes quantization-induced norm
+            distortion, improving PPL by ~0.8% at 4-bit.
+    """
+
+    head_dim: int = 128
+    key_quant_bits: int = 3  # 3-4 = MSE keys, 8 = FP8 keys
+    value_quant_bits: int = 4  # 3-4 = uniform quantized values
+    seed: int = 42
+    norm_correction: bool = False
+
+    @property
+    def key_fp8(self) -> bool:
+        """Whether keys are stored as FP8 — no rotation/quantization needed."""
+        return self.key_quant_bits == 8
+
+    @property
+    def mse_bits(self) -> int:
+        """MSE quantizer bit-width (determines centroid count: 2^mse_bits).
+
+        For MSE key modes, equals key_quant_bits.
+        For FP8 key mode, falls back to value_quant_bits (centroids are still
+        needed for continuation-prefill dequant and decode kernel params).
+        """
+        if self.key_fp8:
+            return self.value_quant_bits
+        return self.key_quant_bits
+
+    @property
+    def key_mse_bits(self) -> int:
+        """MSE bits actually used for key quantization (0 if FP8 keys)."""
+        if self.key_fp8:
+            return 0
+        return self.key_quant_bits
+
+    @property
+    def centroid_bits(self) -> int:
+        """Bits for centroid generation — always non-zero."""
+        return self.mse_bits
+
+    @property
+    def n_centroids(self) -> int:
+        return 2**self.mse_bits
+
+    @property
+    def key_packed_size(self) -> int:
+        """Packed bytes for a single KEY vector.
+
+        FP8 mode (key_quant_bits=8):
+          head_dim bytes (1 byte per element, no overhead).
+
+        TQ mode:
+          - MSE indices: ceil(head_dim * key_mse_bits / 8) bytes
+          - vec_norm:     2 bytes (float16)
+        """
+        if self.key_fp8:
+            return self.head_dim  # 1 byte per element
+        mse_bytes = math.ceil(self.head_dim * self.key_mse_bits / 8)
+        norm_bytes = 2  # vec_norm fp16
+        return mse_bytes + norm_bytes
+
+    @property
+    def effective_value_quant_bits(self) -> int:
+        """Actual bits used for value storage."""
+        return self.value_quant_bits
+
+    @property
+    def value_packed_size(self) -> int:
+        """Packed bytes for a single VALUE vector.
+
+        Uniform quantization: ceil(head_dim * bits / 8) + 4 bytes (scale + zero fp16).
+        """
+        data_bytes = math.ceil(self.head_dim * self.value_quant_bits / 8)
+        return data_bytes + 4  # +2 scale(fp16) +2 zero(fp16)
+
+    @property
+    def slot_size(self) -> int:
+        """Total packed bytes per head per position (key + value combined).
+
+        Layout: [key_packed | value_packed]
+        """
+        return self.key_packed_size + self.value_packed_size
+
+    @property
+    def slot_size_aligned(self) -> int:
+        """Slot size rounded up to next even number.
+
+        Even-number is required so effective_head_size = slot_size_aligned // 2
+        is integral.
+        """
+        s = self.slot_size
+        return s + (s % 2)  # round up to even
+
+    @staticmethod
+    def get_boundary_skip_layers(num_layers: int, n: int = 2) -> list[str]:
+        """Get layer indices to skip TQ compression (boundary protection).
+
+        Returns first N and last N layer indices as strings, suitable for
+        kv_cache_dtype_skip_layers.
+        """
+        if n <= 0 or num_layers <= 0:
+            return []
+        n = min(n, num_layers // 2)  # don't skip more than half
+        first = list(range(n))
+        last = list(range(num_layers - n, num_layers))
+        # Deduplicate (if num_layers <= 2*n)
+        indices = sorted(set(first + last))
+        return [str(i) for i in indices]
+
+    @staticmethod
+    def from_cache_dtype(cache_dtype: str, head_dim: int) -> "TurboQuantConfig":
+        """Create config from a named preset.
+
+        Valid presets: turboquant_k8v4, turboquant_4bit_nc, etc.
+        """
+        if cache_dtype not in TQ_PRESETS:
+            valid = ", ".join(TQ_PRESETS.keys())
+            raise ValueError(
+                f"Unknown TurboQuant cache dtype: {cache_dtype!r}. "
+                f"Valid presets: {valid}"
+            )
+        preset = TQ_PRESETS[cache_dtype]
+        return TurboQuantConfig(
+            head_dim=head_dim,
+            key_quant_bits=preset["key_quant_bits"],
+            value_quant_bits=preset["value_quant_bits"],
+            norm_correction=preset["norm_correction"],
+        )

vllm/model_executor/layers/quantization/turboquant/quantizer.py

+# SPDX-License-Identifier: Apache-2.0
+# SPDX-FileCopyrightText: Copyright contributors to the vLLM project
+"""TurboQuant quantizer utilities.
+
+Serving path uses generate_wht_signs() for WHT rotation sign buffers.
+Triton kernels handle all quantization, packing, and dequantization on GPU.
+"""
+
+import torch
+
+_CPU = torch.device("cpu")
+
+
+def generate_wht_signs(d: int, seed: int, device: torch.device = _CPU) -> torch.Tensor:
+    """Generate deterministic random ±1 signs for WHT rotation.
+
+    Used with Walsh-Hadamard Transform for per-layer rotation randomization.
+    Same seed derivation as QR (per-layer via seed + layer_idx * stride).
+    """
+    gen = torch.Generator(device="cpu")
+    gen.manual_seed(seed)
+    bits = torch.randint(0, 2, (d,), generator=gen, device="cpu")
+    signs = bits.float() * 2 - 1
+    return signs.to(device)

vllm/platforms/cuda.py

@@ -255,6 +255,11 @@ class CudaPlatformBase(Platform):
         valid_backends_priorities = []
         invalid_reasons: dict[AttentionBackendEnum, tuple[int, list[str]]] = {}
 
+        # TurboQuant KV cache: route directly to TQ backend
+        kv_cache_dtype = attn_selector_config.kv_cache_dtype
+        if kv_cache_dtype is not None and kv_cache_dtype.startswith("turboquant_"):
+            return [(AttentionBackendEnum.TURBOQUANT, 0)], {}
+
         backend_priorities = _get_backend_priorities(
             attn_selector_config.use_mla,
             device_capability,

vllm/platforms/xpu.py

@@ -61,6 +61,12 @@ class XPUPlatform(Platform):
             "only NHD layout is supported by XPU attention kernels."
         )
 
+        # TurboQuant KV cache: route directly to TQ backend
+        kv_cache_dtype = attn_selector_config.kv_cache_dtype
+        if kv_cache_dtype is not None and kv_cache_dtype.startswith("turboquant_"):
+            logger.info_once("Using TurboQuant attention backend.")
+            return AttentionBackendEnum.TURBOQUANT.get_path()
+
         dtype = attn_selector_config.dtype
         if attn_selector_config.use_sparse:
             logger.info_once("Using XPU MLA Sparse backend.")

vllm/utils/torch_utils.py

@@ -42,6 +42,10 @@ STR_DTYPE_TO_TORCH_DTYPE = {
     "fp8_per_token_head": torch.uint8,
     "fp8_inc": torch.float8_e4m3fn,
     "fp8_ds_mla": torch.uint8,
+    "turboquant_k8v4": torch.uint8,
+    "turboquant_4bit_nc": torch.uint8,
+    "turboquant_k3v4_nc": torch.uint8,
+    "turboquant_3bit_nc": torch.uint8,
 }
 
 TORCH_DTYPE_TO_NUMPY_DTYPE = {