10 things you need to know before the opening bell (SPY, SPX, QQQ, DIA, ROKU)

Yellen testifies. Federal Reserve Chair Janet Yellen will give her economic outlook before the Joint Economic Committee, beginning at 10 a.m. ET.

The pound is rallying after the UK reportedly agrees to a Brexit bill. The British pound trades up 0.49% at 1.3406 versus the US dollar following reports that the United Kingdom and the European Union agreed to a Brexit "divorce bill" worth about 50 billion pounds.

Oil is sliding ahead of OPEC. Brent crude oil, the international benchmark, trades down 1.15% at $62.64 a barrel ahead of Thursday's meeting of OPEC ministers that is expected to lead to an extension of the production cuts introduced last November.

Bitcoin is closing in on $11,000. The cryptocurrency crossed the $10,900 level less than 24 hours after clearing $10,000 for the first time.

The head of the London Stock Exchange is out. CEO Xavier Rolet is leaving "with immediate effect" after losing a shareholder battle.

Uber's loss widens. The ride-hailing app's loss widened from $1.1 billion in the second quarter to $1.46 billion in the third quarter, Bloomberg reports, citing people with knowledge of the matter.

Short seller Andrew Left is targeting Roku. The Twitter account of Andrew Left's Citron Research fired out a series of tweets on Tuesday suggesting that Roku, the video-streaming-device maker that has gained more than 200% since its initial public offering in September, was a "total joke."

Stock markets around the world are higher. Japan's Nikkei (+0.49%) led the gains in Asia and Germany's DAX (+0.8%) paces the advance in Europe. The S&P 500 is set to open little changed near 2,629.

Earnings reporting is light. Tiffany reports ahead of the opening bell.

US economic data keeps coming. GDP — Second Estimate will be released at 8:30 a.m. ET before pending-home sales and the Fed's Beige Book cross the wires at 10 a.m. ET and 2 p.m. ET. The US 10-year yield is up 1 basis point at 2.34%.