A company with roth conversion of PRE tax contributions inside of its 401k ?

Anyone know of a company with a 401k plan with roth conversion available for PRE tax contributions ? This is separate from a different somewhat common plan feature of roth conversion for AFTER tax contributions to assist a so called mega back door roth. Yes I know something like what I am asking can be done in IRA but then you cant put it back inside an ERISA protected 401K.

I'm not sure if I'm understanding the thrust of your question correctly. In my experience in the industry, the vast majority of in-plan Roth conversions are, in fact, from pre-tax funds. The "mega back door Roth" is a niche used by a far smaller number of plans. But at any rate, the answer is yes, you can have a provision in your plan to convert pre-tax contributions, and many do.

9 hours ago, Belgarath said:

yes, you can have a provision in your plan to convert pre-tax contributions, and many do

agree 100% - but in order to allow this the plan must first have a Roth deferral provision.

I think what you're referring to is called an Internal Roth Rollover. I agree with everyone above, in order to do this there has to be 2 elements within the 401k plan:

1- The plan has to allow Roth Deferrals

2- The plan has to allow Internal Roth Rollovers in the plan 

If you have these two elements, you should be able to do the IRR within the plan. 

You also said "Yes I know something like what I am asking can be done in IRA but then you cant put it back inside an ERISA protected 401K." I'm assuming you're asking is someone did a Roth Conversion from their Traditional IRA into a Roth IRA can they roll the Roth IRA into the 401k plan? If that's your question, the answer is no. Roth IRAs are not portable. Once a Roth IRA (outside of Roth Contributions that can be recharacterized), it will always be a Roth IRA. Hope this helps