Mistral Medium 3.5 128B Released: Dense Model with Configurable Reasoning and Vision

Mistral AI has released Mistral Medium 3.5 (128B), a dense transformer model that replaces Mistral Medium 3.1 and Magistral in Le Chat, and Devstral 2 in their coding agent Vibe. It's a single set of weights handling instruction-following, reasoning, and coding.

Key Features

• Dense 128B parameters — not Mixture of Experts.
• 256k context window for long inputs.
• Multimodal input: accepts text and images; outputs text only. Vision encoder trained from scratch to handle variable sizes and aspect ratios.
• Configurable reasoning effort: toggle per request between instant reply (none) and deep reasoning (high).
• Native function calling and JSON output for agentic workflows.
• Multilingual: supports English, French, Spanish, German, Italian, Portuguese, Dutch, Chinese, Japanese, Korean, Arabic, and others.
• Strong system prompt adherence.

Recommended Settings

• Reasoning effort: none for quick replies; high for complex prompts and agentic usage (e.g., reasoning_effort="high").
• Temperature: 0.7 with high reasoning; 0.0–0.7 with none depending on desired creativity.

License

Released under a Modified MIT License — open-source for commercial and non-commercial use, with exceptions for large revenue companies.

GGUF Quantizations Available

Unsloth has published a GGUF version on Hugging Face: unsloth/Mistral-Medium-3.5-128B-GGUF

This model is relevant for developers running local AI coding agents, particularly those needing high-quality instruction following, reasoning, and vision in a single dense model with a large context window.