The model, which to most people is the far more important part, is not open source according to the criteria set by the Open Source Initiative. They own the trademark and police the Open Source® definition. It is fairly clear.

DeepSeek’s list of restrictions on use of their model puts them in a similar position to Meta’s LLama License is still not Open Source. I don’t think it makes sense to say a binary blob is either auditable or is source code but you can say the same of any LLM. There is no way to check the provenance or replicate it or re-build it.

The code they released is under an approved Open Source licence. The MIT licence is very permissive and is compatible with and can be incorporated into closed source and free software while being neither itself. No argument there.