One US official, quoted in The New York Times, joked that the summit was a "bi-latte" rather than a formal bilateral meeting.
Hours before Mr Biden was due to land in Northern Ireland to mark the 25th anniversary of the Good Friday Agreement, No 10 Downing Street denied Mr Sunak’s interactions with Mr Biden in Northern Ireland would be “low-key”.
The Prime Minister will greet the US President when he lands in Air Force One on Tuesday and the two leader's will hold talks in Belfast on Wednesday.
The White House, though, has made efforts to scale back their meeting from a bilateral to a less formal coffee, The New York Times reported.
Mr Sunak will not attend Mr Biden’s main engagement in Northern Ireland — a speech at Ulster University on Wednesday.
Asked why the plans appeared low-key, a No 10 spokesman said on Tuesday: “I wouldn’t characterise it as that. As I’ve said, the Prime Minister will see him tonight, he will see him again tomorrow.
“You’ve seen the President’s actions during his time demonstrate that we have a close relationship. His first visit outside of North America was to the UK, where he met both the queen and the prince of Wales.”
“We continue to have an incredibly positive working relationship with the President and the US government.”
During the talks, Mr Sunak would raise the UK’s “enduring partnership” with the US, trade, investment and other areas of shared interest, the government spokesman added.
He played down the prospect of negotiations being reopened on a post-Brexit free-trade deal with the US, saying this was “not the only way of strengthening the UK-US trade relationship”.
A free-trade deal with the world’s largest economy was originally touted as one of the potential prizes for leaving the European Union but talks have stalled.
Mr Biden’s visit has been timed to coincide with the 25th anniversary of the Good Friday Agreement and Mr Sunak said he was focusing on fulfilling the promise of the peace deal.
Aides to Mr Biden said he would speak to Northern Ireland's political leaders to hail the peace deal and encourage economic ties to the US.
In a speech on Wednesday he will give a shout-out to "the youth generation in Northern Ireland" and "the impact that they’re having economically and domestically, politically," said his top national security spokesman John Kirby.
He downplayed suggestions that Mr Biden would seek to persuade the Democratic Unionist Party to return to power-sharing at the Stormont parliament, which has been in limbo for months.
Mr Sunak was not planning to meet Northern Ireland's political leaders while in the region, but Downing Street denied this was a sign he had given up on getting the DUP back into power-sharing.