They will have a little more time to answer questions than in the earlier debates - one minute and 15 seconds for direct responses to questions and 45 seconds for rebuttals. Also, ABC has decided that candidates will be allowed to make opening statements, but there will be no closing statements as there has been in previous debates.
A live-stream of the debate will be available on this ABC station's website.
ABC News will also livestream the debate beginning at 7 PM ET on its 24/7 digital site ABC News Live as well as ABC.com and the ABC app. Univision News will also livestream the debate on its digital platforms including Facebook, YouTube and Periscope.
In Tonight's Democratic Debate a Promise of Something 'Big'
It appears Harris has lost her post-debate boost - where she fell right behind behind Biden in one poll where she earned 20 per cent to his 22 per cent.
This poll marks one of the only times that Biden has been in jeopardy of losing his front-runner status. So this is the first time their dueling visions for the Democratic Party's future will be contrasted onstage.
The other candidates trailing Warren, Biden and Sanders, while all receiving lower favorable ratings, had relatively high non-response rates, indicating that their inability to achieve ratings comparable to Biden and Warren may be, in part, due to their relative obscurity.
To qualify for Thursday's debate, candidates had to amass 130,000 unique donors, double the amount needed to qualify for the debates earlier this summer. Still, Democratic strategists see Biden as a fragile front-runner, and he has to have solid outings in these coming debates that will likely get more attention than the first couple of rounds. Her standard campaign pitch doesn't mention Biden but is built around an assertion that the "time for small ideas is over", an implicit criticism of more moderate Democrats who want, for example, a public option health care plan instead of single-payer or who want to repeal Trump's 2017 tax cuts but not necessarily raise taxes further. That could give candidates their largest audience yet as the campaigning heads into the fall. And O'Rourke and Castro have what some might consider home-state advantage, as both are from Texas. I'd expect him to be very outspoken as much as he can be and push his message of earnest passion for various progressive causes.
And although Klobuchar's campaign has attracted donors from across the country, no state has given in greater numbers than Minnesota, according to the most recent round of campaign finance reports, filed in July. Candidates have to reach the same criteria as Thursday's debate to qualify, but the field is already looking bigger.