What changed with DeepSeek V3.1

DeepSeek V3.1 combined thinking and non-thinking behavior in one model. The August 21, 2025 announcement also described improvements to tool use and multi-step tasks, with a 128K context window for both modes ^[1].

Two modes at launch

At that release, deepseek-chat selected the non-thinking mode and deepseek-reasoner selected the thinking mode. The announcement also documented support for the Anthropic API format and strict function calling in the beta API ^[1].

These names are important when reading old examples, but they are not permanent version pins.

Check what the API name means now

DeepSeek's change log records later upgrades to those same API names, including V3.1-Terminus and V3.2-Exp ^[2]. Copying a 2025 request with deepseek-chat therefore does not prove that a current request runs the original V3.1 model.

When comparing results, record the provider's model mapping, the date and which mode was used. For historical research, use the release announcement to describe V3.1 and the change log to follow what replaced it. Keep the provider's performance claims separate from results you have measured on your own task.