Employers are allowed to reimburse employees, for tuition, up to $5250, per year, tax free. Anything over that is taxable and included as taxable income on your W-2. So, if your employer waits until the end, then only $5250 of the total tuition will be tax free.
Assuming the MBA program is multi-year, it would be better if he reimbursed you each year. That way, $5250 each year is tax free.
But, as the other answer indicates, if you employer treats the money as business expense reimbursement, rather than tuition reimbursement, it can all be tax free. But, certain conditions (described in the other answer) must be met to call it business expenses.
For a discussion on claiming the tuition credit, see https://ttlc.intuit.com/questions/4521474-can-i-claim-my-mba-as-an-expense-if-my-employer-is-providi... In general, you may not claim a tuition credit if you are reimbursed with tax free money.
