GitHub DeepSeek: https://github.com/marketplace/models/azureml-deepseek/DeepSeek-R1

Get a key here:
https://github.com/settings/personal-access-tokens
Type any name
Pick "No expiration"
Click "Generate Token"

Copy your token into ST (use custom) and use https://models.inference.ai.azure.com for your endpoint.
It has no model list, so paste DeepSeek-R1 into the Model ID section.
You're limited to 1 message per minute and it seems quite slow but it's better than nothing.

If you want to try any other Github models, go here https://github.com/marketplace?type=models and click on any model. Click "Use this model" and find the modelName line which should have what you need to use that model in ST.