DeepSeek 4.1 is a generation of large language models developed by DeepSeek, introduced through the release of DeepSeek-V4.1-Flash on September 10, 2026. The released model accepts images and text and produces text, combining multimodal understanding with reasoning, programming, and tool-using capabilities. Its architecture emphasizes efficient processing of long inputs and AI agent workloads. The generation name should be distinguished from the specific Flash model and from deepseek-flash, the identifier used to access it through DeepSeek’s application programming interface (API). (api-docs.deepseek.com)
Release and naming
DeepSeek-V4.1-Flash followed the V4 generation, whose Pro and Flash preview models were released on April 24, 2026. The September release replaced V4-Flash and the experimental V4-Flash-Vision-Exp in the hosted API. Their older identifiers, deepseek-v4-flash and deepseek-v4-flash-vision-exp, were retained temporarily as compatibility aliases routing requests to V4.1-Flash. These aliases therefore do not necessarily identify the original models. (api-docs.deepseek.com)
The September launch announcement discussed a prospective V4.1-Pro model, but that reference was not itself a release announcement for such a model. Subsequent API documentation continued to list V4-Pro separately and stated that its service would remain available after September 14, 2026, revising the originally announced migration plan. (api-docs.deepseek.com)
Architecture
DeepSeek-V4.1-Flash uses a mixture-of-experts architecture with 552 billion backbone parameters. Its 40-layer Transformer is divided into a 20-layer causal encoder and a 20-layer decoder. Approximately 8 billion parameters are activated per token during input processing and 16 billion during output generation; these active counts are distinct from the model’s stored parameter count. (huggingface.co)
The causal encoder–decoder architecture derives the decoder’s global key–value cache from the encoder’s final hidden states. Compressed Sparse Attention 2 shares cached representations and sparse-selection information across layers. Together with low-precision caching, these mechanisms reduce memory requirements during inference. A vision encoder converts images into representations processed jointly with text. (huggingface.co)
Capabilities and access
DeepSeek’s hosted service specifies a one-million-token context window and a maximum output of 384,000 tokens. It supports thinking and non-thinking modes, tool calls, structured JSON output, and multiple API formats. These are documented service limits and features rather than a guarantee that every deployment offers identical settings. (api-docs.deepseek.com)
Image input enables picture description, reading text in screenshots, and chart analysis. Supported image formats include JPEG, PNG, GIF, and WebP. The documented multimodal interface combines image and text inputs with textual responses; it is not an image-generation interface. (api-docs.deepseek.com)
The model weights and accompanying repository are distributed under the MIT License. DeepSeek also provides reference inference and prompt-encoding implementations, enabling deployment outside its hosted service. (huggingface.co)
Evaluation and limitations
DeepSeek’s published results include scores of 90.9 on GPQA Diamond, 90.6 on Terminal-Bench 2.1, and 74.2 on DeepSWE v1.1. These are developer-reported benchmark results, not measures of universal accuracy. The model card specifies maximum reasoning effort for its instruction-model evaluations and identifies the agent frameworks used. It also reports different outcomes across frameworks, illustrating the importance of the surrounding software system when interpreting agent performance. (api-docs.deepseek.com)
Hosted access has additional operational constraints. The Responses API is stateless: clients must supply conversation history for subsequent turns rather than rely on server-stored conversations. API compatibility, available context, and tool integration are therefore separate considerations from the underlying model’s architecture. (api-docs.deepseek.com)
References
- DeepSeek-V4.1-Flash: Smarter, Faster, More Efficientapi-docs.deepseek.com
- Models & Pricingapi-docs.deepseek.com
- DeepSeek V4 Preview Releaseapi-docs.deepseek.com
- Change Logapi-docs.deepseek.com
- README.md · deepseek-ai/DeepSeek-V4.1-Flash at mainhuggingface.co
- Visionapi-docs.deepseek.com
- Responses APIapi-docs.deepseek.com