I checked the CDC website - here is the relevant information:
If you plan to travel internationally, you will need to get a COVID-19 viral test (regardless of vaccination status or citizenship) no more than 1 day before you travel by air into the United States. You must show your negative result to the airline before you board your flight. The 1-day period is 1 day before the flight’s departure. The Order uses a 1-day time frame instead of 24 hours to provide more flexibility to the air passenger and aircraft operator. By using a 1-day window, test acceptability does not depend on the time of the flight or the time of day that the test sample was taken. For example, if your flight is at 1pm on a Friday, you could board with a negative test that was taken any time on the prior Thursday.
Air passengers will also be required to confirm in the form of an attestation that the information they present is true.
You must be tested with a viral test to look for current infection – these include an antigen test or a nucleic acid amplification test (NAAT).
Phrases indicating a test is an antigen test could include, but not are not limited to:
Rapid antigen test
Viral antigen test
Rapid tests are acceptable if they are a viral test that meet the requirements under the Order.
You can use a self-test (sometimes referred to as home test) that meets the following criteria:
The test must be a SARS-CoV-2 viral test (nucleic acid amplification test [NAAT] or antigen test) with Emergency Use Authorization (EUA) from the U.S. Food and Drug Administration (FDA) OR the relevant national authority where the test is administered.
The testing procedure must include a telehealth service affiliated with the manufacturer of the test that provides real-time supervision remotely through an audio and video connection. Some FDA-authorized self-tests that include a telehealth service may require a prescription.
The telehealth provider must confirm your identity, observe the sample collection and testing procedures, confirm the test result, and issue a report that meets the requirements of CDC’s Order (see “What information must be included in the test result?” below).
Airlines and other aircraft operators must be able to review and confirm your identity and the test result details. You must also be able to present the documentation of test results to U.S. officials at the port of entry and local/state health departments, if requested.
A test result must be in the form of written documentation (paper or digital copy). The documentation must include:
Type of test (indicating it is a NAAT or antigen test)
Entity issuing the result (e.g., laboratory, healthcare entity, or telehealth service)
Sample collection date
A negative test result must show the sample was taken no more than 1 day before the flight.
A positive test result for documentation of recovery from COVID-19 must show the sample was taken within the 90 days before the flight.
Information that identifies the person (full name plus at least one other identifier such as date of birth or passport number)
Test result
Before boarding a flight to the U.S., you will need to show a paper or digital copy of your test result for review by the airline and may be requested to show to public health officials after you arrive in the U.S.