2026. You are still in business, don't close your business on your 2025 tax return.
Money is counted as income when you receive it in a form that you can use, even if you don't use it. For example, if you receive a check in the mail on December 31, 2025, it is 2025 income even if you don't deposit it until 2026. (But, it would not be 2025 income if it was post-dated, or if the payer told you not to deposit it right away because their account was overdrawn, because the money wouldn't really be yours at that moment.)
On the other hand, if they mail a check in 2025 but you do not receive it until 2026, it is 2026 income for you even though it might be a 2025 expense for them.
If you receive 1099s from these payers and they include the payments as 2025 payments even though you don't receive them until 2026, you could report them as 2025 income to avoid a mis-match in the records (although that is technically incorrect, and the IRS is used to people reporting different amounts due to timing issues like this). Any checks mailed in 2026 that will be reported on a 2026 1099 are definitely 2026 income and you can't report it early for the sake of convenience.
