From the research I did it appears that the two plans are similar but there are a few things that set them apart from each other.
- 401a plans are generally offered to government employees while 401k are offered by companies in the private sector.
- 401a contributions are usually mandatory while 401k are optional
- Investments in a 401a are generally more conservative than the ones in a 401k
I read several different articles on the topic but they all pretty much summed it up the same way.
Feel free to refer to this article from SoFi for more information.
Hope this helps.