With an LLM, the actual 0s and 1s of the model are fairly standard, common, and freely available to anyone that wants to use them. The "source code" for an LLM, is the process used to create the outcome, and to an extent, the data used to train with. DeepSeek released a highly detailed paper that describes the process used to create the outcome. People/Companies are actively trying to reproduce the work of DeepSeek to confirm the findings.

It's more akin to scientific research where everyone is using the same molecules, but depending on the process you put the molecules through, you get a different outcome.