DeepSeek

DeepSeek is a family of open-weight models from the Chinese lab of the same name, released under a permissive MIT license, which is about as open as open-weight gets on the usage side. It made waves by matching much pricier closed models on reasoning and coding while costing a fraction to run.

There's a general model and a reasoning-focused one that shows its thinking as it works. You can run it on your own hardware with the usual local tools, or use its cheap API. The pitch is frontier-ish quality at a price that changes the math.

Use it when cost matters and you still want strong reasoning or coding, whether through its low-priced API or self-hosted. The MIT license makes it one of the easier open models to use commercially without license worry.

It's a Chinese model, so some organizations have data-governance or policy concerns about the hosted version, worth checking against your own rules. Self-hosting sidesteps most of that, since the weights run entirely on your infrastructure.