Your total cost basis information will be on Form 1099-B, which will be available by Feb. 16, 2021.
The 1099-B will list your total cost basis information, broken out between short-term and long-term transactions. Detailed cost basis information for each sale transaction will be available on subsequent pages of the form.
Note that although you can run your own cost basis or realized gains reports in your account, these are not official tax forms.
Betterment is not a tax advisor, nor should any information herein be considered tax advice. Please consult a qualified tax professional.