Historical model page: This page covers DeepSeek V3.1 as a historical DeepSeek release from August 2025. It is kept for release context, model-history research, open-weight reference, and older API-alias interpretation. It is not a live hosted API model-selection guide, pricing guide, or deployment checklist.
Last reviewed: April 24, 2026
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DeepSeek V3.1 was introduced on August 21, 2025 as an important step in the DeepSeek V3 model line. It is best understood as the release that brought a single-model hybrid setup to the V3 family, with both thinking and non-thinking behavior, stronger tool-use behavior, improved agent-oriented workflows, and a 128K context window.
This article intentionally treats DeepSeek V3.1 as a timeline page. It explains what V3.1 introduced, how the release was described by DeepSeek at the time, how the hosted API aliases were mapped during that release period, and why old V3.1 references should not be copied into new implementation material without checking live documentation.
DeepSeek V3.1 at a Glance
| Page scope | Historical overview of DeepSeek V3.1 |
|---|---|
| Release date | August 21, 2025 |
| Model line | DeepSeek V3 family |
| Main release theme | Hybrid thinking and non-thinking behavior in one model |
| Total parameters | 671B |
| Activated parameters | 37B |
| Context length | 128K |
| Open-weight availability | DeepSeek published DeepSeek V3.1 and DeepSeek V3.1 Base model cards with downloadable weights. |
| Model-card license | The DeepSeek V3.1 Hugging Face model card lists the repository and model weights under the MIT License. |
| Historical API mapping at release | During the V3.1 release period, deepseek-chat mapped to non-thinking mode and deepseek-reasoner mapped to thinking mode. |
| Archive note | This page documents V3.1 in its release-period context and does not identify any live hosted API model as the default choice. |
Where DeepSeek V3.1 Fits in the Timeline
DeepSeek V3.1 sits between the earlier V3-family releases and later DeepSeek updates. It matters because it combined two behavior modes into one model and became a reference point for later work on tool use, agents, long-context behavior, and API migration history.
| Date | Milestone | Why it matters historically |
|---|---|---|
| Before August 2025 | Earlier V3-family releases | Provided the V3 foundation that V3.1 built upon. |
| August 21, 2025 | DeepSeek V3.1 release | Introduced hybrid inference: thinking and non-thinking behavior in one model, plus stronger tool and agent behavior. |
| September 22, 2025 | DeepSeek V3.1-Terminus update | Built on V3.1 with improvements focused on language consistency, output stability, and stronger Code Agent and Search Agent behavior. |
| September 29, 2025 | DeepSeek V3.2-Exp release | Marked a later experimental stage built on the V3.1-Terminus path, showing that the hosted roadmap moved beyond the original V3.1 release. |
| December 1, 2025 | DeepSeek V3.2 release | Appears here only as later timeline context after V3.1, not as the subject of this page. |
What DeepSeek V3.1 Introduced
DeepSeek V3.1 was presented as a refinement of the V3 line with a stronger focus on hybrid behavior, tool use, agent workflows, and long-context operation. Its most important historical contributions were practical rather than purely branding-related.
- Hybrid inference: V3.1 supported both thinking and non-thinking behavior within one model.
- Two release-period API behaviors: the hosted API mapping at launch used non-thinking behavior for
deepseek-chatand thinking behavior fordeepseek-reasoner. - 128K context: DeepSeek’s release materials described 128K context for both API behaviors, and the model card listed 128K context for DeepSeek V3.1 and DeepSeek V3.1 Base.
- Improved tool use: the release notes emphasized stronger tool use and multi-step agent tasks after post-training.
- Updated chat template: the model card documented thinking and non-thinking chat-template patterns, including different assistant prefixes for each mode.
- Long-context extension: the model card described V3.1 Base as built from the V3 base checkpoint through a two-phase long-context extension process.
- Open-weight release: DeepSeek published open-weight model cards for DeepSeek V3.1 and DeepSeek V3.1 Base.
Hybrid Thinking and Non-Thinking Modes
The defining V3.1 concept was hybrid behavior. Instead of presenting thinking and non-thinking behavior as completely separate model families, V3.1 supported both modes within one model design.
In non-thinking mode, the chat-template format used a prefix ending with </think>. In thinking mode, the format used a prefix ending with <think>. This distinction is important for readers studying V3.1 locally, reviewing the tokenizer configuration, or interpreting archived examples.
For hosted API usage, old alias mappings should be treated as release-period history. Hosted API aliases can be updated, redirected, deprecated, or retired over time, so historical V3.1 alias behavior should not be assumed to remain valid outside its release context.
Tool Use and Agent Behavior
DeepSeek described V3.1 as a step toward stronger agent workflows. The release notes emphasized post-training gains in tool use and multi-step agent tasks, while the model card documented tool-call formats and examples for code-agent and search-agent style workflows.
This matters historically because V3.1 helped connect the V3 line to more agent-oriented usage patterns. It also explains why older discussions about V3.1 often mention tool use, search workflows, code-agent tasks, and multi-step reasoning.
Open-Weight Release vs Hosted API
DeepSeek V3.1 appears in two different contexts that should not be blurred:
- Open-weight model context: the DeepSeek V3.1 model card documents downloadable weights, model structure, chat-template behavior, local-running notes, evaluation tables, and licensing information.
- Hosted API release context: the DeepSeek API release note described how hosted API aliases mapped to V3.1 behavior at the time of the August 2025 release.
The open-weight context is useful for local experimentation, model research, citation, and historical comparison. The hosted API context is useful for understanding old examples and release-period API behavior. Neither context should be treated as a permanent statement about live API routing, pricing, or availability.
What Changed After DeepSeek V3.1
After the original V3.1 release, DeepSeek continued the same broad roadmap with additional updates. V3.1-Terminus followed in September 2025 with improvements focused on language consistency, output stability, and stronger agent behavior. Later releases moved the public roadmap further away from the original V3.1 release.
This is why the page should be read as a historical archive. DeepSeek V3.1 remains important for understanding the model timeline, but it should not be described as the latest release, the live default hosted model, or the primary recommendation for new hosted API examples.
Who Should Read This Page
- Readers studying the DeepSeek V3 model timeline
- Researchers comparing V3.1 with earlier and later DeepSeek releases
- Builders interpreting old API examples, release notes, or alias mappings from 2025
- Users looking for historical context around thinking and non-thinking behavior
- Developers reviewing the V3.1 open-weight model card, tokenizer configuration, or chat-template notes
- Writers documenting how DeepSeek’s model family evolved through long-context, tool-use, and agent-focused updates
How to Use This Historical Page Correctly
Use this page to understand what DeepSeek V3.1 was, what it introduced, how it was described at launch, and how it fits into the DeepSeek model timeline.
Do not use this page as the only source for live model IDs, production API code, hosted API costs, account behavior, app availability, rate limits, or migration instructions. For those details, use the official DeepSeek documentation and Chat-Deep.ai’s actively maintained guide pages.
- Chat-Deep.ai Models hub
- Chat-Deep.ai API guide
- Chat-Deep.ai pricing page
- DeepSeek for coding guide
- Official DeepSeek API change log
- Official DeepSeek API model list
- Official DeepSeek models and pricing documentation
Official Sources Checked
This article was reviewed against official DeepSeek and DeepSeek model-card sources. Recheck the sources below before updating implementation examples, pricing language, or hosted API claims.
- Official DeepSeek V3.1 release note
- Official DeepSeek V3.1 model card on Hugging Face
- Official DeepSeek V3.1-Terminus update
- Official DeepSeek V3.2-Exp release note
- Official DeepSeek V3.2 release note
- Official DeepSeek API change log
FAQ
What is DeepSeek V3.1?
DeepSeek V3.1 is a historical DeepSeek V3-family release introduced in August 2025. It is known for supporting thinking and non-thinking behavior in one model, improving tool-use behavior, and maintaining a 128K context window.
Is this page a live API implementation guide?
No. This page is an archive-style overview of DeepSeek V3.1. It should not be used as the only source for live model IDs, hosted API costs, production code examples, or migration decisions.
Why does this page mention old API aliases?
The aliases are mentioned because they were part of the V3.1 release-period API mapping. They are included for historical interpretation only. Hosted API aliases can change over time, so old V3.1 mappings should not be treated as permanent implementation instructions.
Can I study or run the DeepSeek V3.1 open weights?
Yes, DeepSeek published DeepSeek V3.1 model-card materials and downloadable weights. Before running, fine-tuning, deploying, or redistributing any checkpoint, review the exact model card, hardware requirements, tokenizer notes, chat-template instructions, and license terms.
Where should I check live DeepSeek API details?
Use the official DeepSeek API documentation, official change log, official model list, official pricing page, and Chat-Deep.ai’s actively maintained Models, API, and Pricing pages. This V3.1 page is for historical context only.
Final Takeaway
DeepSeek V3.1 remains important because it marked a major V3-family step toward hybrid thinking and non-thinking behavior, stronger tool use, agent-oriented workflows, and long-context model usage.
Read this page as a DeepSeek V3.1 historical archive. It explains what the release introduced and how it fits into the DeepSeek timeline, without presenting V3.1 as the latest hosted model, the live default API model, or the recommended model name for new implementation examples.