Mistral-Medium-3.5-128B

by Mistral

Mistral Medium 3.5 is a dense 128 billion parameter model released April 2026, handling instruction-following, reasoning, and coding in a single set of weights with a configurable reasoning effort. With a 256k token context window and an open-weight release under a modified MIT license, it balances frontier capability with self-hosting accessibility on as few as four GPUs. Built for agentic systems and software development, the model consolidates Mistral's prior reasoning, coding, and chat lines, supporting function calling, agent orchestration, structured outputs, and multimodal understanding. It scores 77.6% on SWE-Bench Verified, making it well suited to autonomous systems, reasoning-heavy applications, and complex coding tasks.

Key info

Input
Output
Features
Context window
β€”
Max output
β€”
Input price
$1.71 /1M
Output price
$5.70 /1M
  • EU residency available
  • Zero data retention on pay-as-you-go
  • No training by default
  • GDPR DPA available

Available routes

Mistral-Medium-3.5-128B runs on 2 different routes through the Opper gateway. Compare residency, ZDR, and training posture at a glance β€” full data-handling detail per route below.

ProviderRegionZero data retentionTrainingInputOutput
EUZero data retentionNo$1.71$5.70
EUZero data retentionNo$1.71$6.84

Training posture across routes: No training on prompts by default.

Data handling per route

Each route hosting Mistral-Medium-3.5-128B has its own privacy posture, residency, and GDPR terms. Postures are maintained by Opper with a last-verification timestamp.

Berget β€” SwedenπŸ‡ΈπŸ‡ͺ

Zero data retention is on by default on Pay-as-you-go β€” no action required. No training on customer data. EU; DPA available.

Zero data retention
On by default on Pay-as-you-go.
Training
No training on customer data.
Logging
None
Third-party access
None disclosed
GDPR DPA
DPA available
Transfer mechanism
Not applicable β€” data stays in EU

Evroc β€” SwedenπŸ‡ΈπŸ‡ͺ

Zero data retention is on by default on Pay-as-you-go β€” no action required. No training on customer data. EU; DPA available.

Zero data retention
On by default on Pay-as-you-go.
Training
No training on customer data.
Logging
Abuse monitoring
Third-party access
None disclosed
GDPR DPA
DPA available
Transfer mechanism
Not applicable β€” data stays in EU

Get started

Call Mistral-Medium-3.5-128B through the Opper gateway with one API key. Let your coding agent set it up, or call it directly β€” Opper is drop-in compatible with the OpenAI, Anthropic, and Google AI SDKs.

Set it up with your agent

Copy this and paste it into your coding agent β€” Claude Code, Cursor, Codex, and more β€” and it'll wire up Opper for you.

Or call it directly

import OpenAI from "openai";
const client = new OpenAI({
apiKey: process.env.OPPER_API_KEY,
baseURL: "https://api.opper.click/v3/compat",
});
const completion = await client.chat.completions.create({
model: "berget/mistralai/Mistral-Medium-3.5-128B",
messages: [{ role: "user", content: "Hello" }],
});
console.log(completion.choices[0].message.content);

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Mistral-Medium-3.5-128B by Mistral β€” pricing, benchmarks, ZDR, EU hosting | Opper AI