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---
title: Mistral Medium 3.5
metatags:
description: "Deploy Mistral Medium 3.5 with SGLang - 128B dense flagship merged model with hybrid reasoning, 256K context, vision input, and FP8 quantization."
---
import { MistralMedium35Deployment } from '/src/snippets/autoregressive/mistral-medium-3-5-deployment.jsx';
## 1. Model Introduction
**Mistral Medium 3.5** is Mistral AI's first flagship **merged model** — a single dense 128B checkpoint that handles instruction following, reasoning, and coding in one set of weights. It replaces Mistral Medium 3.1 and Magistral in Le Chat, and replaces Devstral 2 in the Vibe coding agent. Reasoning effort is configurable per request, so the same model can answer a quick chat reply or work through a deep agentic run. The vision encoder was trained from scratch to handle variable image sizes and aspect ratios.
**Key Features:**
- **Dense 128B parameters** — no MoE, no MLA, plain GQA (96 heads, 8 KV heads, head_dim=128)
- **256K context window** — YARN RoPE scaling on top of the original 4K base
- **Hybrid Reasoning**: Toggle between instant reply and deep reasoning per request via `reasoning_effort` (`"none"` or `"high"`)
- **Vision**: Accepts text + image input; from-scratch encoder that handles variable image sizes/aspect ratios
- **Function Calling**: Native tool calling and JSON output
- **FP8 Native**: Released with FP8 e4m3 static-tensor quantization built in
- **Multilingual**: 24 supported languages including English, French, German, Spanish, Portuguese, Italian, Japanese, Korean, Russian, Chinese, Arabic, Persian, Indonesian, Malay, Nepali, Polish, Romanian, Serbian, Swedish, Turkish, Ukrainian, Vietnamese, Hindi, and Bengali
- **License**: Modified MIT (open for commercial and non-commercial use except for companies with large revenue)
**Architecture:**
- Mistral 3 backbone with YARN RoPE for 256K context
- Dense (no MoE), 128B parameters
- Standard GQA attention (not MLA)
- Pixtral-style vision encoder (48 layers, patch_size=14, spatial_merge=2, image_size=1540) trained from scratch
- Multimodal input: text + image
**Models:**
- **[mistralai/Mistral-Medium-3.5-128B](https://huggingface.co/mistralai/Mistral-Medium-3.5-128B)** (FP8)
The HuggingFace repo ships both the mistral native layout (`params.json` + `consolidated-*.safetensors`) and the HF layout (`config.json` + `model-*.safetensors`). SGLang auto-detects the format — the HF layout is preferred when both are present.
---
## 2. SGLang Installation
SGLang offers multiple installation methods. You can choose the most suitable installation method based on your hardware platform and requirements.
Please refer to the [official SGLang installation guide](../../../docs/get-started/install) for installation instructions.
---
## 3. Model Deployment
### 3.1 Basic Configuration
**Interactive Command Generator**: Use the configuration selector below to generate a launch command for Mistral Medium 3.5.
<MistralMedium35Deployment />
### 3.2 Configuration Tips
- **Tensor Parallelism**: Mistral Medium 3.5 FP8 (~130 GB) requires `--tp 4` on Hopper (H100/H200) and `--tp 2` on Blackwell (B200/B300).
- **Reasoning effort**: Reasoning depth is configurable per request via `reasoning_effort` (`"none"`, `"high"`). No restart required — toggle per call.
- **Recommended temperature**: `0.7` when `reasoning_effort="high"`. Anywhere from `0.0` to `0.7` when `reasoning_effort="none"`, depending on the task — lower for to-the-point answers, higher for creative output.
- **Context length vs memory**: The model has a 256K context window. If you are memory-constrained, lower `--context-length` (e.g. `32768`) and increase once things are stable.
- **Tool calling**: Enable `--tool-call-parser mistral` to activate native function calling support.
- **Reasoning parser**: Enable `--reasoning-parser mistral` to separate `reasoning_content` from the main response content.
- **System prompt**: The model ships with a recommended system prompt in `chat_template.jinja` and `SYSTEM_PROMPT.txt`. If you do not pass a system message yourself, the chat template injects Mistral's default (model identity, current date, tool-use guidelines). For full fidelity with Mistral's reference setup, load `SYSTEM_PROMPT.txt` from the HF repo and substitute `{name}`, `{today}`, `{yesterday}` (see Section 4.6).
---
## 4. Model Invocation
### 4.1 Thinking Mode
Mistral Medium 3.5 is a hybrid reasoning model. By default it does not produce a reasoning trace — pass `reasoning_effort="high"` to switch on the deep-reasoning path. Mistral recommends `temperature=0.7` for reasoning mode.
```python Example
from openai import OpenAI
client = OpenAI(
base_url="http://localhost:30000/v1",
api_key="EMPTY",
)
response = client.chat.completions.create(
model="mistralai/Mistral-Medium-3.5-128B",
messages=[
{"role": "user", "content": "Solve step by step: what is 17 × 23 + 144 / 12?"},
],
temperature=0.7,
extra_body={"reasoning_effort": "high"},
)
print("Reasoning:", response.choices[0].message.reasoning_content)
print("Answer:", response.choices[0].message.content)
```
**Output:**
```text Output
Reasoning: I need to follow the order of operations (PEMDAS/BODMAS): multiplication and
division before addition, evaluated left to right.
17 × 23: I'll break it as 17 × (20 + 3) = 340 + 51 = 391.
144 / 12 = 12.
Finally, 391 + 12 = 403.
Answer: **17 × 23 + 144 / 12 = 403**
Step by step:
1. 17 × 23 = 391
2. 144 / 12 = 12
3. 391 + 12 = 403
```
### 4.2 Instruct Mode (Reasoning Off)
To skip the reasoning trace and get a fast direct response, set `reasoning_effort="none"`. For instruct mode, Mistral recommends temperature in the `0.0`–`0.7` range depending on how creative the task is:
```python Example
from openai import OpenAI
client = OpenAI(
base_url="http://localhost:30000/v1",
api_key="EMPTY",
)
response = client.chat.completions.create(
model="mistralai/Mistral-Medium-3.5-128B",
messages=[
{"role": "user", "content": "What is the capital of France?"},
],
temperature=0.1,
extra_body={"reasoning_effort": "none"},
)
print(response.choices[0].message.content)
```
**Output:**
```text Output
The capital of France is **Paris**. It is one of the most famous and visited cities in
the world, known for its rich history, art, culture, and landmarks like the Eiffel Tower,
Louvre Museum, and Notre-Dame Cathedral.
```
### 4.3 Streaming with Reasoning
```python Example
from openai import OpenAI
client = OpenAI(
base_url="http://localhost:30000/v1",
api_key="EMPTY",
)
stream = client.chat.completions.create(
model="mistralai/Mistral-Medium-3.5-128B",
messages=[
{"role": "user", "content": "Explain the difference between async and threading in Python."},
],
temperature=0.7,
extra_body={"reasoning_effort": "high"},
stream=True,
)
print("=== Reasoning ===")
for chunk in stream:
delta = chunk.choices[0].delta
if hasattr(delta, "reasoning_content") and delta.reasoning_content:
print(delta.reasoning_content, end="", flush=True)
elif delta.content:
print("\n=== Response ===")
print(delta.content, end="", flush=True)
print()
```
### 4.4 Tool Calling
Mistral Medium 3.5 supports native function calling. Enable with `--tool-call-parser mistral`:
```python Example
from openai import OpenAI
client = OpenAI(
base_url="http://localhost:30000/v1",
api_key="EMPTY",
)
tools = [
{
"type": "function",
"function": {
"name": "get_weather",
"description": "Get the current weather for a city",
"parameters": {
"type": "object",
"properties": {
"location": {"type": "string", "description": "City name"},
"unit": {"type": "string", "enum": ["celsius", "fahrenheit"]},
},
"required": ["location"],
},
},
}
]
response = client.chat.completions.create(
model="mistralai/Mistral-Medium-3.5-128B",
messages=[{"role": "user", "content": "What's the weather in Paris?"}],
tools=tools,
tool_choice="auto",
)
tool_calls = response.choices[0].message.tool_calls
for tc in tool_calls:
print(f"Tool: {tc.function.name}")
print(f"Args: {tc.function.arguments}")
```
**Output:**
```text Output
Tool: get_weather
Args: {"location": "Paris"}
```
### 4.5 Vision (Image Input)
Mistral Medium 3.5 accepts image inputs alongside text. The vision encoder was retrained from scratch to handle variable image sizes and aspect ratios:
```python Example
from openai import OpenAI
client = OpenAI(
base_url="http://localhost:30000/v1",
api_key="EMPTY",
)
response = client.chat.completions.create(
model="mistralai/Mistral-Medium-3.5-128B",
messages=[
{
"role": "user",
"content": [
{"type": "text", "text": "Describe what you see in this image."},
{
"type": "image_url",
"image_url": {"url": "https://raw.githubusercontent.com/sgl-project/sglang/main/assets/logo.png"},
},
],
}
],
temperature=0.7,
extra_body={"reasoning_effort": "none"},
)
print(response.choices[0].message.content)
```
**Output:**
```text Output
The image features a stylized representation of the acronym "SGL." The letters
are large, bold, and orange with a brown outline, giving them a three-dimensional
effect. To the left of the letters, there is a graphic that resembles a neuron
or a node with connections, also in a similar orange and brown color scheme. The
node has a code symbol (</>) inside a square, suggesting a connection to
programming or technology.
```
### 4.6 Loading the Reference System Prompt
Mistral ships a `SYSTEM_PROMPT.txt` alongside the weights. The reference setup loads it from the HF repo and substitutes `{name}`, `{today}`, and `{yesterday}` at runtime so the model knows its identity and the current date. SGLang's chat template will inject a default system prompt if you omit one, but for full parity with Mistral's reference, load it explicitly:
```python Example
from datetime import datetime, timedelta
from huggingface_hub import hf_hub_download
from openai import OpenAI
MODEL = "mistralai/Mistral-Medium-3.5-128B"
def load_system_prompt(repo_id: str, filename: str = "SYSTEM_PROMPT.txt") -> str:
path = hf_hub_download(repo_id=repo_id, filename=filename)
today = datetime.today().strftime("%Y-%m-%d")
yesterday = (datetime.today() - timedelta(days=1)).strftime("%Y-%m-%d")
name = repo_id.split("/")[-1]
with open(path) as f:
return f.read().format(name=name, today=today, yesterday=yesterday)
client = OpenAI(base_url="http://localhost:30000/v1", api_key="EMPTY")
response = client.chat.completions.create(
model=MODEL,
messages=[
{"role": "system", "content": load_system_prompt(MODEL)},
{"role": "user", "content": "Write me a sentence where every word starts with the next letter in the alphabet — start with 'a' and end with 'z'."},
],
temperature=0.1,
extra_body={"reasoning_effort": "none"},
)
print(response.choices[0].message.content)
```
---
## 5. Benchmarks
Validation runs on 4× H200 with `--tp 4`, served via the `/v1/chat/completions` endpoint.
### 5.1 Accuracy Benchmarks
#### GSM8K
```bash Command
python3 benchmark/gsm8k/bench_sglang.py --port 30000
```
**Results:**
```text Output
Accuracy: 0.945
Invalid: 0.000
Latency: 13.594 s
Output throughput: 1560.660 token/s
```
#### MMMU
```bash Command
python3 benchmark/mmmu/bench_sglang.py --port 30000
```
**Results:**
```text Output
Overall accuracy: 0.586
```
### 5.2 Speed Benchmarks
#### Latency (Low Concurrency)
```bash Command
python3 -m sglang.bench_serving \
--backend sglang \
--dataset-name random \
--num-prompts 10 \
--max-concurrency 1 \
--random-input-len 1024 \
--random-output-len 512 \
--port 30000
```
**Results:**
```text Output
============ Serving Benchmark Result ============
Backend: sglang
Successful requests: 10
Benchmark duration (s): 38.86
Total input tokens: 6101
Total generated tokens: 2684
Output token throughput (tok/s): 69.07
Mean E2E Latency (ms): 3883.80
Median TTFT (ms): 95.90
Median TPOT (ms): 14.19
==================================================
```
#### Throughput (High Concurrency)
```bash Command
python3 -m sglang.bench_serving \
--backend sglang \
--dataset-name random \
--num-prompts 1000 \
--max-concurrency 100 \
--random-input-len 1024 \
--random-output-len 512 \
--port 30000
```
**Results:**
```text Output
============ Serving Benchmark Result ============
Backend: sglang
Successful requests: 1000
Benchmark duration (s): 117.28
Total input tokens: 512842
Total generated tokens: 262023
Output token throughput (tok/s): 2234.18
Total token throughput (tok/s): 6607.01
Mean E2E Latency (ms): 11303.79
Median TTFT (ms): 152.95
Median TPOT (ms): 42.53
==================================================
```