What do you mean? Your W-2, and your eligiblilty to contribute to a 401k, should be based on payroll that was actually paid in calendar year 2023, regardless of when the money was earned (when you performed the work).
If your W-2 is definitely incorrect, you have three options.
1. File with incorrect information and amend later. This is the worst choice, because amended returns take 6 months to process, and I would not trust the IRS to handle the 401k issue correctly, it could come back to bite you when you retire.
2. Wait and file when you have the corrected W-2. This is the best option. As long as you don't owe income tax, there is no penalty for filing late. If you do owe, and it is too late to get an extension, pay your tax bill as soon as you can, as this will limit any eventual penalties and interest (you will include the payment on your return when you file so you will get a refund of any overpayment).
3. File now using the "substitute W-2" (there is a box to check for "my W-2 is incorrect" and you can then fill out a substitute W-2 with what you believe is the correct information. However, if your eventual corrected W-2 differs from your substitute W-2, you would still need to file an amended return later.
