He's probably asking about stocks, as there is now a lot of activity in some stocks starting at 4 AM EST. It is usually the momo stocks from the previous day, but a lot of stocks are gapping up at this time. FWIW, TD Ameritrade lets you begin pre-market trading at 7 AM EST.
Yes stocks is what I am asking about. @CET yeah I am aware of the volume issues I am looking to trade special situations.
You are asking a very straightforward question. 400am EST time is around the start of the European session. There are thousands of Asian, European, Middle East, and even the American brokers that are open during this time. most brokers operate almost 24 hours a day because they want to let traders trade the Asian, European, Middle East, and US sessions. You can easily go to google for the 400am EST brokers. Most of the traders would recommend IB as it operates almost 24 hours a day, and they cover various financial products from various countries.
there are not thousands of brokers. Since the The poster is in the US he is not likely looking for Asian/European brokers if he is posting on ET. https://www.brokerage-review.com/online-brokers/extended-hours-trading.aspx