DeepSeek V4.1 Flash (Reasoning, Max Effort)

DeepSeek V4.1 Flash is a multimodal sparse Mixture-of-Experts (MoE) model and the inaugural release in the developer's Causal Encoder-Decoder (CED) architecture family. Released in September 2026, it is designed to achieve a high intelligence ceiling at a reduced inference cost, specifically targeting agentic workflows, long-context reasoning, and complex coding tasks. The model natively supports both text and image inputs, processing visual and linguistic data within a unified 552B-parameter backbone.

The model's architecture employs an asymmetric activation strategy, utilizing 8B active parameters during prefill and 16B active parameters during decoding. This design, combined with Compressed Sparse Attention 2 (CSA2) and a main KV cache in FP4, significantly reduces the memory footprint compared to previous generations. The KV cache efficiency is reported to be approximately four times higher than the previous DeepSeek-V4 Flash, facilitating the handling of its 1 million token context window while maintaining high throughput.

The "Reasoning, Max Effort" configuration refers to the model's highest reasoning intensity, corresponding to a reasoning_effort value of 100. This mode is optimized for high-difficulty tasks where the model performs extensive internal chain-of-thought processing before generating an answer. Benchmarks at this effort level indicate performance exceeding previous flagship "Pro" iterations in domains such as software engineering (DeepSWE v1.1) and terminal-based agent operations (Terminal-Bench 2.1), reaching a Codeforces rating of 3471.

DeepSeek V4.1 Flash is released under an MIT license with open weights available for self-hosting. It replaces earlier specialized variants like the V4 Flash and V4 Flash Vision Exp, consolidating their features into a single native multimodal model. It is particularly suited for long-horizon task completion and agentic use cases that require multi-step reasoning over large datasets.