turbo-attn 0.26.0

Optimized CUDAgraph-enabled kernels and attention backend for vLLM, SGLang and more based on TurboQuant near-lossless KV cache compression. SOTA performance with Gemma 4, Qwen 3.6 and other modern LLMs.

Turbo Attention

The KV-cache backend for VRAM-constrained inference. Fit ~3.75× more context into the same GPU, at decode-parity speed. Serve it on arbi-serve — our own OpenAI-compatible inference engine, where TKV is a native first-class backend — or on our thin vLLM / SGLang forks.

PyPI: turbo-attn · Import: tkv · License: MPL-2.0

# same flags on all three supported engines (arbi-serve / vLLM-fork / SGLang-fork):
<engine> serve <model> --kv-cache-dtype tkv --attention-backend turbo-attn

---

Why turbo-attn

Attention is memory-bound and the KV cache is what eats your VRAM. turbo-attn attacks that directly: a near-lossless 2/4/8-bit KV codec (TurboQuant) welded to custom prefill + decode kernels that dequantize inline, so you pay for the compression in bytes stored, not in tokens/sec.

1 · Fit far more context in the same VRAM

The headline. Cross-engine chat-serving baseline on Qwen3.6-27B-AWQ-INT4, TP=2 on 2× RTX 4090 (locked clocks, single-tenant, prefix-caching OFF, cudagraph, real prompts):

engine / KV codec	c1 tok/s	c8 tok/s	KV-cache tokens	density
SGLang / bf16	76.5	317.9	340,539	1×
SGLang / tkv	73.1	307.5	1,282,029	3.76×
vLLM / bf16	75.0	338.6	317,290	1×
vLLM / tkv	75.1	330.3	1,190,272	3.75×

Same card, ~3.75× the resident context — at decode parity (the dequant is amortized under cudagraph; ~13 ms TPOT is the model's memory-bandwidth roofline either way). That is longer prompts, more concurrent sequences, or a bigger model on the hardware you already have.

• SmartMix per-layer allocation. TKV_BITS is an average bits-per-element target; a calibrated solver gives each layer its own (k_bits, v_bits) over the full 2–8-bit range, and the kernels read that heterogeneous cache in a single forward pass — closer to bf16 at equal memory. See SmartMix.
• Near-lossless, verified. Correctness is gated on PPL / needle / task-accuracy against a bf16+FlashAttention control arm — not vibes.
• Big-model shapes covered. GQA, sliding-window, MTP (multi-token predict), and MLA (DeepSeek V2/V3/V4) are all first-class.

2 · Fast, bit-identical kernels — no speed tax

Compressing the KV cache only pays off if the kernel can read it compressed. Decompress to a bf16 buffer before attention and the memory savings never materialize — you write the decompressed cache back through HBM and hand back, in bandwidth, every byte you just saved. turbo-attn's kernels instead dequantize inline, inside the MMA pipeline, so the compressed bytes are the only thing that crosses HBM and the dequant hides under the math. That is precisely why ~3.75× smaller KV comes at decode parity rather than a speed penalty — the codec's memory win and the kernel's speed are the same win.

On prefill the custom arbi split-D mainloop goes further, beating the FlashAttention-4 mainloop it grew out of by 1.2–1.4× geomean, bit-identically, across Ada / Blackwell / Ampere (and at or above stock FlashAttention-2 on raw bf16). Those kernels also run uncompressed bf16 / fp16 (BypassLoader) — so turbo-attn is a fast general attention backend on its own, and that raw-bf16 path is where the FA4 / FA2 comparisons are measured like-for-like (no codec confound). Everything runs under full CUDAGraph capture.

See The kernels for the per-kernel innovation breakdown.

3 · Built for fast iteration & developer-friendliness

turbo-attn is designed to be adopted and extended without forking the world:

• First-class in arbi-serve; a thin overlay elsewhere. On arbi-serve, our own inference engine, TKV is a native backend — nothing to fork. For vLLM and SGLang we ship small forks, because neither upstream can yet register a new KV-cache dtype / attention backend at runtime; once the fork is installed, enabling TKV is a single --kv-cache-dtype tkv flag via an auto-registered plugin entry-point. (HuggingFace Transformers is used only as a correctness oracle — a bf16 reference arm — not a serving path.)
• Two pieces you can consume separately (see below) — take the pure-PyTorch codec with any attention backend, or take the kernels with any KV format.
• One clean extension point — the Loader Protocol. Adding a new KV format (fp8, int8, nvfp4, GPTQ, …) is a sibling module, not mainloop surgery. You write the per-tile SMEM-fill body; the scheduler, softmax, and epilogue stay ours. See docs/writing_a_loader.md for a complete worked fp8 example.
• Hackable codec. TurboKVCodec is pure PyTorch with a Triton/CUDA fast path and a readable fallback — easy to read, ablate, and unit-test on CPU.
• Apples-to-apples by construction. BypassLoader runs raw bf16/fp16 through the byte-identical kernel, so codec-vs-baseline ablations isolate exactly one variable.
• Turn-key ops. A Dockerfile per engine (docker compose up), auto-calibration on first init, and a "just-works" config surface with optimal-by-default settings and loud, named, validated caps.

---

Install

pip install turbo-attn                  # codec + CUDA/Triton kernels
pip install "turbo-attn[vllm]"          # + vLLM attention backend
pip install "turbo-attn[all]"           # + SGLang, FlashInfer, flash-attn, eval harness

Quickstart

import torch
from tkv import TurboKVCodec

codec = TurboKVCodec(head_dim=128, bit_width=4, device="cuda")
keys = torch.randn(8, 128, device="cuda")

packed, norms = codec.compress_k(keys)
recon = codec.decompress_k(packed, norms)

See examples/ for runnable snippets and ARCHITECTURE.md for a codebase tour.

Two independently-usable pieces

turbo-attn ships two pieces that are sold as a stack but designed to be consumed separately:

1. Codec → any attention backend. TurboKVCodec is a pure, framework-agnostic compressor: compress with TKV, decompress to bf16 / fp16, hand the result to vanilla flash_attn_varlen_func, FlashInfer, SGLang attention, anything that takes raw KV. See examples/06_tkv_codec_with_third_party_attention.py.

2. Kernels → any KV format. The cute-DSL prefill and split-K paged decode kernels are policy-parametric on the K/V format via the Loader extension point. The bundled set is {TkvLoader, BypassLoader}:

   • TkvLoader — TKV centroid-based codec dequant (the production path).
   • BypassLoader — raw bf16 / fp16 KV, no codec. Useful for apples-to-apples ablations under an otherwise-byte-identical kernel. Third-party formats (fp8, int8, nvfp4, …) are not shipped — write a sibling Loader for your format. The Loader is the public extension surface; mainloop / scheduler / softmax / epilogue stay turbo-attn's. See docs/writing_a_loader.md for a worked fp8 example.

Repo layout

• tkv/ — the package (codec, kernels, runtime, vLLM/SGLang plugins, calibration pipeline).
• tkv/kernels/loaders/ — bundled cute-DSL prefill Loaders (tkv, bypass).
• tkv/kernels/_decode_loader_*.cuh — bundled decode Loaders (TkvDecodeLoader, BypassDecodeLoader).
• docs/, docker/, scripts/, examples/, experiments/ — public docs, deploy recipes, helper scripts, runnable examples, research notes.
• The top-level internal/ directory is engineering-only and unsupported — design notes, internal compose files, dev harnesses. It is kept in-tree for development history but excluded from the wheel (MANIFEST.in prune internal), so it never ships.

Run with Docker

Three inference servers are supported: vLLM, SGLang, and arbi-serve. Each ships a turn-key Dockerfile. Calibration files for the bit-width / model combo go in a host directory; the TKV_CALIBRATION_FILE env var inside the container points to one. Examples below use Qwen3.5-0.8B + a K4V4 calibration.

Layout assumed

/path/to/models/Qwen3.5-0.8B/...                       # HF snapshot
/path/to/calibrations/qwen3.5-0.8b_k4v4.json           # calibration bundle

All three accept the same CLI flags: --kv-cache-dtype tkv --attention-backend turbo-attn plus TKV_BITS=<float> and TKV_CALIBRATION_FILE=<path>. TKV_BITS is the average bits-per-element across K and V (e.g. 4.0, 5.0, 6.0); a per-layer Lagrangian solver turns that target into a per-layer (k_bits, v_bits) allocation that lives in the calibration bundle. TKV_BITS=4.0 does not mean "K and V both at 4 bits" — it means "average 4 bits-per-element under the smart per-layer allocation".

Sibling-checkout layout

All three Dockerfiles COPY from a sibling-repo layout. Clone the relevant repos as siblings of turbo-attn/:

GIT/
├── turbo-attn/        # this repo
├── vllm-fork/         # arbicity/vllm-turbo        (only needed for vLLM image)
├── sglang-fork/       # arbicity/sglang-turbo      (only needed for SGLang image)
└── arbi-serve/        # arbi-dev/arbi-serve  (only needed for arbi-serve image)

mkdir -p ~/GIT && cd ~/GIT
git clone https://github.com/arbi-dev/turbo-attn
git clone https://github.com/arbicity/vllm-turbo       vllm-fork    # for vLLM
git clone https://github.com/arbicity/sglang-turbo     sglang-fork  # for SGLang
git clone https://github.com/arbi-dev/arbi-serve              # for arbi-serve

vLLM

Uses our vllm-fork rebased onto upstream v0.20.1 (small overlay — CacheDType Literal relaxation, per-group block-pool bookkeeping, named TURBO_ATTN slot in AttentionBackendEnum; full layout in docker/PATCHES.md).

cd ~/GIT/turbo-attn/docker

# build + run
TKV_MODELS_ROOT=/path/to/models \
  docker compose -f compose.vllm.yaml up -d --build

docker compose -f compose.vllm.yaml logs -f

# serve a request once "Application startup complete" appears:
curl http://localhost:8000/v1/completions \
  -H "Content-Type: application/json" \
  -d '{"model": "/models/Qwen3.5-0.8B", "prompt": "The capital of France is", "max_tokens": 12, "temperature": 0}'

Optional env (override on the docker compose command line):

Variable	Default	Purpose
TKV_MODEL	/models/Qwen3.5-0.8B	Container-side model path
TKV_BITS	4.0	Average bits-per-element target
TKV_CALIBRATION_FILE	unset	Path to a calibration bundle. Unset → uniform K4V4 fallback (tests/CI only; production needs a bundle)
TKV_PORT	8000	Host port
TKV_GPU_DEVICE	0	NVIDIA_VISIBLE_DEVICES
TKV_MAX_MODEL_LEN	2048	Max context length

SGLang

Uses our sglang-fork rebased onto upstream v0.5.11 (small overlay — plugin registries for KV-cache dtypes and attention backends; full layout in docker/PATCHES.md).

cd ~/GIT/turbo-attn/docker

TKV_MODELS_ROOT=/path/to/models \
  docker compose -f compose.sglang.yaml up -d --build

docker compose -f compose.sglang.yaml logs -f

curl http://localhost:30000/v1/completions \
  -H "Content-Type: application/json" \
  -d '{"model": "/models/Qwen3.5-0.8B", "prompt": "The capital of France is", "max_tokens": 12, "temperature": 0}'

Same env-var contract as vLLM (drop TKV_MAX_MODEL_LEN; SGLang uses TKV_CONTEXT_LEN and TKV_MEM_FRAC for --mem-fraction-static, default 0.45).

arbi-serve

Standalone OpenAI-compatible server with TKV backends as a first-class citizen. Lives in arbi-dev/arbi-serve.

cd ~/GIT/arbi-serve

ARBI_MODELS_ROOT=/path/to/models \
  docker compose up -d --build

docker compose logs -f

curl http://localhost:8000/v1/completions \
  -H "Content-Type: application/json" \
  -d '{"model": "/models/Qwen3.5-0.8B", "prompt": "The capital of France is", "max_tokens": 12, "temperature": 0}'

MLA models

For DeepSeek V2/V3/V4, additionally set -e TKV_MLA_ENABLE=1 on whichever container.

Calibration

Pre-built calibration bundles for common models live in HuggingFace at arbi-dev/turbo-attn-calibrations. To roll your own:

python -m tkv.calibration.calibrate_centroids \
    --model Qwen/Qwen3.5-0.8B \
    --output qwen3.5-0.8b_k4v4.json \
    --bit-width 4

How it works

1. Rotate each KV vector with a fast Walsh–Hadamard transform.
2. Normalize — store the magnitude as a single BF16 value.
3. Quantize each rotated coordinate to a shared codebook.

Attention scores on rotated KV are bit-identical to attention on unrotated KV when the query is rotated by the same matrix; we pre-rotate Q once per request and compute everything in the rotated space.

The kernels

The kernels are where the codec turns from a storage trick into a serving win. Each is a substantial piece of engineering in its own right; the throughline is inline dequant.

Inline dequant — why the codec's savings actually survive

A naive integration decompresses the packed KV to a bf16 tensor before attention. That round-trip writes the decompressed cache back through HBM — paying back every byte the codec saved, and erasing the bandwidth win that makes KV compression worth doing on a memory-bound kernel.

turbo-attn's kernels never materialize a decompressed KV tensor. Both the prefill mainloop and the decode kernel unpack + dequantize inside the MMA pipeline, tile by tile, straight into SMEM/registers. Only the compressed bytes cross HBM; the dequant math hides under the matmul. This is the single most important property in the repo — it is what makes "3.75× smaller cache" and "decode-parity throughput" the same fact instead of a trade-off.

The seam that keeps this reusable is the Loader Protocol (see Two independently-usable pieces): the per-tile SMEM-fill body is a compile-time-specialized functor, so the dequant loop is unrolled and any format axes (bit width, scale presence) are dead-code-eliminated against the mainloop. Runtime branches or function pointers in the hot loop would collapse this by an order of magnitude — so there are none.

Also a full bf16 backend — the confound-free baseline

The very same prefill and decode kernels run a BypassLoader: raw bf16 / fp16 KV, no codec, through a byte-identical mainloop / softmax / epilogue. This matters twice:

• turbo-attn is a general attention backend even with the codec off — you can adopt the faster prefill/decode schedules on ordinary uncompressed KV, no calibration, no compression.
• It is where the FlashAttention-4 and FlashAttention-2 comparisons live. FA4 and FA2 consume raw bf16 — and so does the arbi mainloop in bypass mode. The reported 1.2–1.4× over FA4 and the FA2 parity are therefore confound-free, like-for-like schedule wins on identical bf16 inputs, not "our dequant path vs their plain path." The codec-path numbers are measured separately against the same kernel in bypass mode, so the codec's own overhead is isolated on its own axis too.

Prefill — the arbi split-D mainloop

tkv/kernels/cuda/prefill/arbi_prefill.py, the unconditional production prefill path at every head-dim. An original schedule on the same CuTeDSL base as FlashAttention-4 (our tkv/kernels/cute/_fa/ fork of Dao-AILab's flash_attn.cute), not a tuning of it.

• Split-D (head-dim-in-SMEM) sequence-parallel walk — beats the FA4 mainloop bit-identically by 1.2–1.4× geomean across Ada/Blackwell/Ampere (up to 1.6× at head_dim=256), and matches or beats mature stock FA2 on bf16. Because it shares FA4's loader/softmax/epilogue via one cute_prefill entry, the win is pure schedule at zero accuracy cost.
• Inline TQ dequant in the MMA pipeline — K dequants into n-major SMEM as e4m3; V dequants transposed (d-major sVt) so P·V reads it directly with ldmatrix, avoiding a separate transpose pass, and the warps that own the dequant STS also own the pipelining.
• fp8 (e4m3) split-D path (TKV_FA4_SPLITD_FP8) — an fp8 producer for the compute-bound long-context prefill regime.
• First-chunk bypass (TKV_PREFILL_BYPASS, default on) — prompt prefill runs uncompressed, then re-rotates to the TQ basis for decode, so prefill quality is never codec-limited.
• Fallbacks: the FA4 mainloop (TKV_PREFILL_KERNEL=fa4) owns head_dim > 256; a decompress + stock FlashAttention path handles any shape both decline. See Prefill performance for numbers.

Decode — the unified split-K kernel

tkv/kernels/_cuda_decode_unified_splitk.cu, the sole production decode path.

• One fused split-K SIMT kernel — unpack → dequant → Q·K → online-softmax → P·V in a single pass, no decompress buffer.
• One template-policy body serves full attention and sliding-window via a compile-time RangePolicy (autotune branches on sliding_window), plus the MTP-verify BLOCK_M=N path — the earlier standalone BLOCK_M=1 kernel was retired into this one.
• Rotation fusion — TKV_FUSE_QROT folds the Q-rotation prologue in, and rotate_output is folded into the o_proj weights (TKV_O_PROJ_FOLD), so the rotation cost leaves the token loop entirely.
• MLA-shaped decode variant for DeepSeek V2/V3/V4.
• Per-shape autotuner (tkv/runtime/autotune.py) picks split count / MTP variant / fuse_qr per geometry.

Compress-on-the-wire + CUDAGraph

• Fused compress + store (fused_compress_store) encodes K/V and writes the packed cache in a single kernel — compression happens on the write path, never as a separate materialize-then-compress pass.
• Full CUDAGraph capture end-to-end with CG-safe per-step metadata precomputed host-side, so the entire compressed path is invisible at the token level.

SmartMix: per-layer optimal KV, read in one pass

Uniform KV quantization spends the same bits on every layer — but layers are not equally sensitive: some tolerate 3-bit keys with 5-bit values, others the reverse. SmartMix is turbo-attn's per-layer bit-allocation. Given an average bits-per-element budget, a calibrated solver assigns each layer its own (k_bits, v_bits) over the full 2–8-bit range (odd widths included), spending bits where the model's own decode drift says they matter.

Two things make this more than a calibration knob:

• A single forward pass reads a heterogeneous cache. The cache holds a different (k_bits, v_bits) per layer — e.g. layer 15 at K4V3, layer 19 at K5V3, layer 23 at K4V5 — and each layer's attention dispatches to a kernel compile-time-specialized to that layer's widths through the Loader Protocol's geometry-keyed dispatch. No per-token branching, no runtime format check in the hot loop; every width is its own specialized PTX, with CG-safe metadata precomputed host-side so the whole heterogeneous forward still runs under one CUDA graph. We are not aware of another production serving stack that reads per-layer mixed-precision KV natively — most KV-quant implementations are a single width for the entire cache.

• It buys fidelity at equal memory — equivalently, a target fidelity at fewer bits (i.e. a smaller cache). Measured as KL drift from bf16 (lower = closer), SmartMix beats the best-global uniform allocation at the same bytes/token, and the margin grows as compression gets more aggressive (−12.6% at 6 bits, −19.5% at 4 bits, reaching ~−36% at 3.5 bits on the raw-Lloyd bundle):

  ⚠️ Preliminary numbers — Qwen3.5-0.8B, 2026-07-12, correctly baselined vs best-global uniform. A refreshed run is pending; treat the exact values as provisional.

  KV format (equal bytes/tok)	avg bits	KL drift vs bf16 ↓
  bf16 self-jitter floor	16	0.831
  uniform K8V8 (calibrated)	8	1.050
  fp8 e4m3	8	1.466
  uniform K6V6	6	2.122
  SmartMix @ 6.0	6	1.855 (−12.6%)
  uniform K4V4	4	14.409
  SmartMix @ 4.0	4	11.595 (−19.5%)

  The same curve shows calibrated KV beating fp8 — 1.05 vs 1.47 mbits/tok at 8 real bits — so spending the bit-budget on a fitted codebook beats spending it on an fp8 mantissa.

The fidelity win is unambiguous and monotone in the bit-budget. Turning it into a downstream task-accuracy number is gated on running a benchmark hard enough to be KV-limited: at 4 bits the tasks measured so far (NIAH to 131K, GSM8K, math500) put SmartMix and uniform at the bf16 ceiling, so the discriminating benchmark is the open eval item — not a sign the headroom isn't there. Allocations are produced by the solver (python -m tkv.auto_calibrate --solve) and stored in the calibration bundle's byte_budget_table.

Performance

Cross-engine chat-serving baseline on Qwen3.6-27B-AWQ-INT4, TP=2 on 2× RTX 4090, via the canonical chat_baseline.sh/serve_bench.sh harness — locked clocks, single-tenant, prefix-caching OFF, cudagraph, real prompts, vllm bench serve. The decode/density table is in Why turbo-attn above.

MTP (native head, thinking mode, c1): vLLM ~145–147 tok/s, SGLang ~128 — each ~1.7–2× its own no-MTP baseline. The residual ~13% is SGLang's NEXTN per-step overhead at equal draft acceptance (~3.5), not draft quality.

Prefill performance

The arbi prefill mainloop is an original schedule on the FlashAttention-4 CuTeDSL base. Since it and the FA4 mainloop feed the same loader / softmax / epilogue via one cute_prefill entry, they produce bit-identical output — so the wall-clock gap is a pure mainloop win at zero accuracy cost. These comparisons run in bypass (raw bf16) mode — FA4 and stock FA2 see the exact same uncompressed inputs the arbi mainloop does, so the delta isolates the schedule and nothing else (no codec confound). Measured with benchmarks/bench_prefill_splitd_vs_fa4.py (eager, torch.cuda.Event, median of 50, dense causal prefill across head_dim ∈ {64,128,256}, GQA ratios {1,4,7,8}, and both symmetric and asymmetric chunked-prefill shapes 512…131072):

GPU	vs FA4 (bf16 / tkv codec), 42 shapes, Δ=0	vs stock FA2 (bf16)
RTX 4090 (Ada, sm89)	1.29× / 1.21× geomean, 42/42	net-positive (1.00× geomean; FA2 edges asym only)
RTX 5090 (Blackwell, sm120)	1.27× / 1.25× geomean, 42/42	ahead (1.07× geomean, 29/42)
RTX A5500 (Ampere, sm86)	1.44× / 1.18× geomean, 42/42	ahead (1.03× geomean, 27/42)

Two things to read off this: the arbi mainloop decisively and bit-identically beats the FA4 mainloop it replaced across all three GPU generations (up to 1.6× at head_dim=256), and on raw bf16 it is at or above parity with the mature stock FlashAttention-2 — net-positive on every GPU, with the sole soft spot being asymmetric long-prefill on Ada — while being the only one of the two that can serve the compressed TKV codec path at all (FA2 has no inline dequant). Reproduce:

python benchmarks/bench_prefill_splitd_vs_fa4.py --dtypes bf16,tq4 --fa2 --flashinfer

Configuration

All runtime configuration is via TKV_-prefixed environment variables. The supported surface is below; anything unlisted is internal and may change.

Bit width and calibration

Variable	Default	Description
TKV_BITS	4.0	Average bits-per-element target across K and V (float in [2.0, 8.0]). The runtime looks up the calibration bundle's byte_budget_table[<TKV_BITS>] for the per-layer (k_bits, v_bits) allocation. Hard error if the entry is missing — no silent fallback.
TKV_CALIBRATION_FILE	""	Path to a calibration bundle (centroids + per-channel scales + byte_budget_table). Required for production; bundle generation: python -m tkv.auto_calibrate. When unset, the plugin falls back to uniform K4V4 (tests/CI only).
TKV_AUTO_CALIBRATE_MODEL	""	Model path for plugin-side auto-calibration when TKV_CALIBRATION_FILE doesn't exist on first init.

Engine selection

Variable	Default	Description
TKV_ENGINE	"" (auto)	Decode engine: native_tq, flash_attn, or bypass.
TKV_PREFILL_ENGINE	fa4	Prefill family (dispatcher), not the mainloop: fa4 = the CuTeDSL cute_prefill path (default), adaptive = add the decompress+FA fallback for layouts CuTeDSL declines, decomp_fa_main_only = bench-only. Despite the name, fa4 here does not force the FA4 mainloop — see TKV_PREFILL_KERNEL.
TKV_PREFILL_KERNEL	"" (=arbi)	The CuTeDSL mainloop: arbi/unset = the arbi prefill mainloop (production default, every head-dim); fa4 = the FA4 mainloop fallback (also auto-selected at head_dim > 256).
TKV_PREFILL_BYPASS	1	First-chunk prefill bypass — skip codec on prompt-prefill, then re-rotate to TQ basis for decode.
TKV_FUSE_QROT	"" (auto)	Fused Q-rotation prologue. Decode-only.
TKV_O_PROJ_FOLD	on	Fold rotate_output into o_proj weights.
TKV_MTP_SPLITK	1	Use split-K decode kernel for MTP layers.
TKV_DECODE_SPLITS	"" (autotune)	Force decode-kernel split count.

Backend behaviour

Variable	Default	Description
TKV_NO_JIT	0	Fail if a kernel variant is not pre-compiled.
TKV_K_NC	1	Apply norm-correction to K reads in the dequant path.
TKV_DISABLE_PRESCALE	0	Disable per-channel pre-scaling on compress upload.
TKV_STRICT_NO_SDPA	0	Raise instead of taking the head_dim>256 SDPA fallback. Recommended for head_dim>256 deployments.

MLA (DeepSeek V2/V3/V4)

Variable	Default	Description
TKV_MLA_ENABLE	0	Master switch for the MLA backend.
TKV_MLA_ROPE_HEAD_DIM	64	RoPE head dimension for MLA latent + RoPE split.

Why we ship engine forks (for now)

turbo-attn needs each host engine to let a plugin register a new KV-cache dtype and attention backend at runtime. Neither vLLM nor SGLang allows that upstream yet, so we ship thin overlay forks — vllm-turbo and sglang-turbo:

• vLLM — CacheDType in vllm/config/cache.py is a Pydantic Literal validated at class-definition time, which blocks runtime registration of new KV-cache dtypes. Our overlay relaxes it, adds a named TURBO_ATTN backend slot, and per-group block-pool bookkeeping.
• SGLang — needs plugin registries for KV-cache dtypes and attention backends wired into the engine.

Both are thin overlays rebased on tagged upstream releases; full layout in docker/PATCHES.md. arbi-serve needs no overlay — TKV is a native backend there. As upstream gains runtime registration, these forks shrink toward zero.

Citation

If Turbo Attention helps your work, please cite both the underlying TurboQuant paper and this implementation:

@misc{turbo_attention2026,
  title = {Turbo Attention: Production attention backend for TurboQuant KV cache compression},
  author = {Evseev, Dmitri},
  year = {2026},
  url = {https://github.com/arbi-dev/turbo-attn}
}

@inproceedings{zandieh2026turboquant,
  title = {TurboQuant: Near-optimal KV Cache Quantization for LLM Inference},
  author = {Zandieh, Amir and others},
  booktitle = {ICLR},
  year = {2026}
}

License

Mozilla Public License 2.0 (MPL-2.0). See LICENSE and NOTICE.