From Betterment support page:
If you have more than 500 lines of transactions, you might not be able to import via the online version of TurboTax.
Certain versions of tax software limit the number of transaction lines they support for automatic upload. This varies from provider to provider. For example, the online version of TurboTax has a limit of 500 transaction lines.
If you are unable to automatically import your tax forms into your tax software, the IRS allows you to report the summary information on your electronic tax return and send a paper copy of your statement with Form 8453 to the IRS after your tax return has been accepted. If you report your Betterment transactions on Form 8453, you should check the box that says “Form 8949, Sales and Other Dispositions of Capital Assets (or a statement with the same information), if you elect not to report your transactions electronically on Form 8949.”
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