The Duke and Duchess of Sussex and Family, News and Events 10: August 2024 -

[Somebody]

Charles is head of state, Harry is son of head of state, so immediate family.

“Diplomats and Officials Requiring A-1 Visas - Examples:
-Head of State or Government, regardless of the purpose of travel
-Ambassador, Public Minister, Career Diplomat or Consular Officer coming to serve at a foreign embassy or consulate in the United States, such as an ambassador or consul
- Certain government ministers in positions equivalent to U.S. cabinet level secretaries coming to the United States to perform official, government related duties for not more than 90 days
- European Union (EU) and African Union (AU) delegation representatives
- Immediate family members of an A-1 visa holder”

Visas for Diplomats and Foreign Government Officials

travel.state.gov

Charles is not a permanent A1 visa holder who lives in the States and Harry doesn't live or travel with him, so he doesn't qualify for the last example.

I agree with TM, however, that it is not unlikely that he received/s favorable treatment.

 

[Ghost]

I can bet that Charles does not apply for a visa every time he travels to the States. He might have a 10 year long one, he might have an indefinite one. Neither does Harry need to be accompanying his father in order to qualify.

 

[Somebody]

When Harry moved to the States he was only a grandson of a Head of State and so far Charles hasn't even been to the States as king, so, he has had little need for an A1 visa for the last several years.

Requirements to be defined as immediate family - which Harry doesn't meet as he is part of a different household and does not regularly reside in either the late queen Elisabeth's nor king Charles's household:

Immediate family members are defined as the spouse and unmarried sons and daughters up to certain age who are members of your household, even if studying in a different location. An immediate family member may also be any other person who is related by blood, marriage or adoption and will reside regularly in your household, is not a member of some other household, and is recognized as your immediate family member by the sending Government, as demonstrated by eligibility for rights and benefits, such as the issuance of a diplomatic or official passport or travel and other allowances.

Source: Visas for Diplomats and Foreign Government Officials

 

[moby]

He might have an A1 visa if the State Department made an exception due to high-level instructions. However, as a diplomat on an A visa, he’s not allowed to engage in profit-driven activities in the U.S. unless it’s official government business. Given his clear involvement in private, for-profit activities unrelated to the UK government, it's unlikely he’s using an A visa. Engaging in unauthorized business activities on a diplomatic visa would likely draw scrutiny from both immigration and tax authorities, it would be highly risky and an overt violation of visa rules.

ETA: If I were the in the UK Embassy in the US, it would be hugely embarrassing to me as a British diplomat with a prince working in the country while on an A visa.