Step-3.5 Flash (197B-A11B) on B300 288GB Blackwell Ultra (288GB) — VRAM, KV Cache & Throughput

Step-3.5 Flash (197B-A11B) (196.81B total, 11B active, Sparse MoE + GQA) uses 111.33 GiB of 4-bit weights (Q4_K_M), requiring 112.24 GiB total at 8K context and 113.09 GiB at 32K on B300 288GB Blackwell Ultra (~261 tok/s decode).

Interactive Sizing Workbench

Full Compatibility Report →

Open-Weight Model196.81B / 11B

Weights & QuantizationQ4_K_M · 111.33 GiB

Context Window8,192 (8K)

Target Hardware

288 GB · 8000 GB/s

GPU Count (Tensor Parallel)

Concurrent Batch Size

KV Cache Precision

Inference Engine

System RAM Offload (CPU)0%

Fits with Safe Headroom

Config-derived formula HF config.json ↗

Memory Allocation Breakdown (GiB) 112.24 GiB (120.52 GB) / 288 GiB (39%)

Model Weights: 111.33 GiB KV Cache & State: 0.35 GiB Runtime & Activation Buffers: 0.56 GiB System RAM Offload: 0 GiB

Required GPU Memory

112.24 GiB

120.52 GB (decimal)

Usable Hardware Memory

273.6 GiB

288 GB (physical)

Safe Headroom

+161.36 GiB

39% utilization

Est. Decode Throughput

~261 tok/s

11B active params

Est. Prefill Throughput

~24000 tok/s

4K Prompt TTFT: ~171 ms

Est. Cost / 1M Tokens

$2.76

Sparse MoE + GQA · Apache-2.0

Recommended Hardware for Current Configuration

Best Single GPU

Instinct MI300X 192GB (192GB)

~$15,000

Best Value / Used GPU

2x A100 80GB SXM

160GB · ~$24,000

Apple Unified Memory

Mac Studio M4 Ultra 256GB

~$5,999

Cloud From

DigitalOcean · $2.59 / hr

1x Instinct MI300X 192GB

Production Launch Commands

llama.cpp (GGUF)

llama-server -hf stepfun-ai/Step-3.5-Flash:Q4_K_M \
  --ctx-size 8192 -ngl 999 --flash-attn

vLLM

vllm serve stepfun-ai/Step-3.5-Flash \
  --max-model-len 8192 --gpu-memory-utilization 0.92

Live Token Speed Simulator (TTFT ~171ms · ~261 tok/s)

[Step-3.5 Flash (197B-A11B) · 112.24 GiB] allocated on target GPU. Prefill completed in TTFT window; streaming autoregressive tokens at memory-bandwidth-bound rate...

Cloud GPU Comparison & Rent-vs-Buy TCO

Verified public rates across RunPod, Vast.ai, Vultr, and DigitalOcean.

Verified: 2026-11-04

Active usage (hours / day)4 h / day

Local hardware budget ($)

Electricity rate ($/kWh)

Purchase break-even

~35.7 months

Est. local power: $15.96 / mo

Provider	Recommended Instance	Total VRAM	Hourly Rate	Monthly at Selected Hours	Billing Mode	Deploy
RunPod	1x H200 141GB SXM (Community Cloud)	141 GB	$3.59 / hr	$436.54 / mo	Per-second	Deploy GPU ↗
Vast.ai	1x H200 141GB SXM (Verified Host · NVL)	141 GB	$3.87 / hr	$470.47 / mo	Spot / On-demand	Deploy GPU ↗
*Vultr ($300 Free Credit)**	4x L40S 48GB (Dedicated Instance · $300 Credit*)	192 GB	$6.68 / hr	$812.77 / mo	Hourly	Deploy GPU ↗
Vultr Cloud GPU	4x L40S 48GB (Dedicated Instance)	192 GB	$6.68 / hr	$812.77 / mo	Hourly	Deploy GPU ↗
DigitalOcean	1x Instinct MI300X 192GB (Dedicated Instance)	192 GB	$2.59 / hr	$314.94 / mo	Per-second	Deploy GPU ↗

Rates reflect public listings on the verification date and fluctuate with regional inventory.

Fine-Tuning VRAM Requirements (QLoRA / LoRA / Full) — Step-3.5 Flash (197B-A11B)

QLoRA (4b) Fits with Safe Headroom

113.95 GiB

Model Weights: 111.33 GiB · Gradients + Optimizer: 1.54 GiB · Act: 1.08 GiB

Recommended GPU: Instinct MI300X 192GB (192GB)

LoRA (16b) Exceeds Available GPU Memory

370.44 GiB

Model Weights: 366.59 GiB · Gradients + Optimizer: 2.42 GiB · Act: 1.43 GiB

Recommended GPU: 4x H200 141GB SXM (564GB)

Full BF16 Exceeds Available GPU Memory

1505.54 GiB

Model Weights: 366.59 GiB · Gradients + Optimizer: 1136.43 GiB · Act: 2.52 GiB

Recommended GPU: Multi-GPU Required

Engineering Sizing Notes & Optimization Playbook

Quick Hardware Verdict

B300 288GB Blackwell Ultra (288GB physical, 273.6 GiB usable) runs 4-bit (Q4_K_M) Step-3.5 Flash (197B-A11B) at 8K context using 112.24 GiB with 161.36 GiB of safe headroom (~261 tok/s single-stream decode).

KV Cache & Runtime Tuning

Step-3.5 Flash (197B-A11B) uses Sparse MoE + GQA (196.81B total, 11B active per token). Moving from 8K to 32K context expands FP16 KV cache from 0.35 GiB to 1.2 GiB; enabling 8-bit KV cache (llama.cpp -ctk q8_0 -ctv q8_0 or vLLM --kv-cache-dtype fp8) saves 0.6 GiB at 32K (reducing total VRAM to 112.49 GiB).

VRAM Scaling Across Context Windows (4K to 128K, 4-bit Weights)

Model weights remain constant while attention KV cache grows with context length and batch size.

Quantization Precision & Memory Matrix — Step-3.5 Flash (197B-A11B) @ 8K

Quantization Format	Weights (GiB)	KV Cache	Total VRAM (GiB)	Decode Speed	Compatibility (B300 288GB Blackwell Ultra)	Recommended GPU	Data Source
Native Weights (BF16 / FP8 / MXFP4 — Lossless) (BF16)	366.59 GiB	0.35 GiB	367.5 GiB (394.6 GB)	~10.6 tok/s	Exceeds Available GPU Memory	Multi-GPU Required	Official checkpoint size
FP8 / GGUF Q8_0 (8-bit — Near-Lossless) (Q8_0)	194.75 GiB	0.35 GiB	195.66 GiB (210.09 GB)	~198.6 tok/s	Fits with Safe Headroom	Instinct MI325X 256GB (256GB)	Config-derived formula
GGUF Q6_K (6-bit — High Precision) (Q6_K)	150.3 GiB	0.35 GiB	151.21 GiB (162.36 GB)	~227.6 tok/s	Fits with Safe Headroom	Instinct MI300X 192GB (192GB)	Config-derived formula
GGUF Q5_K_M (5-bit — Balanced) (Q5_K_M)	130.47 GiB	0.35 GiB	131.38 GiB (141.07 GB)	~243.5 tok/s	Fits with Safe Headroom	Instinct MI300X 192GB (192GB)	Config-derived formula
Q4_K_M / UD-Q4_K_XL / AWQ (4-bit — Recommended) (Q4_K_M)	111.33 GiB	0.35 GiB	112.24 GiB (120.52 GB)	~261 tok/s	Fits with Safe Headroom	Instinct MI300X 192GB (192GB)	Config-derived formula
GGUF IQ4_XS (4.25-bit — Compact) (IQ4_XS)	97.53 GiB	0.35 GiB	98.44 GiB (105.7 GB)	~275.4 tok/s	Fits with Safe Headroom	Instinct MI300X 192GB (192GB)	Config-derived formula
GGUF Q3_K_M (3-bit — Low VRAM) (Q3_K_M)	89.72 GiB	0.35 GiB	90.63 GiB (97.31 GB)	~284.2 tok/s	Fits with Safe Headroom	Instinct MI300X 192GB (192GB)	Config-derived formula
GGUF UD-Q2_K_XL (2-bit — Extreme MoE) (UD-Q2_K_XL)	63.22 GiB	0.35 GiB	64.13 GiB (68.86 GB)	~318.9 tok/s	Fits with Safe Headroom	RTX PRO 6000 Blackwell (96GB)	Config-derived formula

Technical Specifications & FAQ

Does Step-3.5 Flash (197B-A11B) fit on B300 288GB Blackwell Ultra (288GB)?

In 4-bit (Q4_K_M) at 8,192 context, Step-3.5 Flash (197B-A11B) requires 112.24 GiB total GPU memory (111.33 GiB weights + 0.35 GiB KV cache + 0.56 GiB runtime buffers) against 273.6 GiB usable on B300 288GB Blackwell Ultra, delivering ~261 tok/s decode.

How much VRAM does Step-3.5 Flash (197B-A11B) need at 32K context?

At 32,768 context tokens, Step-3.5 Flash (197B-A11B) (Sparse MoE + GQA) allocates 1.2 GiB for KV cache and state, bringing total 4-bit VRAM to 113.09 GiB (121.43 GB decimal).

Evaluate This Model on Other GPUs

RTX 3060 12GB (12GB)RTX 4060 Ti 16GB (16GB)RTX 4070 Ti Super (16GB)RTX 4080 Super (16GB)RTX 5070 12GB (12GB)RTX 5070 Ti (16GB)RTX 5080 (16GB)RTX 3090 (24GB)RTX 4090 (24GB)RTX 4090 D (24GB)RTX 5090 (32GB)RTX 5090 D (32GB)RTX A6000 (48GB)RTX 6000 Ada (48GB)RTX PRO 6000 Blackwell (96GB)DGX Spark (GB10 128GB) (128GB)L4 24GB (24GB)A40 48GB (48GB)L20 48GB (48GB)L40S 48GB (48GB)A800 80GB SXM (80GB)A100 80GB SXM (80GB)H800 80GB SXM (80GB)H100 80GB SXM (80GB)H20 96GB HBM3 (96GB)H20 141GB HBM3e (141GB)H200 141GB SXM (141GB)B200 180GB (180GB)Ascend 910B 64GB (昇腾) (64GB)Ascend 910C 128GB (昇腾) (128GB)Atlas 300I Duo 96GB (310P) (96GB)MLU590 80GB (寒武纪思元) (80GB)DCU K100-AI 64GB (海光深算) (64GB)MetaX C500 64GB (沐曦曦云) (64GB)Kunlunxin P800 64GB (昆仑芯) (64GB)MTT S4000 48GB (摩尔线程) (48GB)Radeon RX 7900 XTX 24GB (24GB)Radeon AI PRO R9700 32GB (32GB)Ryzen AI Max+ 395 128GB (128GB)Instinct MI300X 192GB (192GB)Instinct MI325X 256GB (256GB)Instinct MI355X 288GB (288GB)Arc Pro B60 24GB (24GB)Gaudi 3 128GB HBM2e (128GB)Mac mini M4 Pro 64GB (64GB)MacBook Pro M4 Max 128GB (128GB)Mac Studio M4 Ultra 256GB (256GB)Mac Studio M3 Ultra 512GB (512GB)

Evaluate Other Models on This Hardware

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