U.S. stock index futures were flat on Wednesday ahead of Nvidia's earnings report, with focus squarely on if the market's recent bull rally that was spearheaded by the AI chip firm and other tech-related shares can be sustained.

Wall Street's main indexes have swung between small gains and losses this week, with the Dow hovering near record highs and the S&P 500 within 1% of an all-time high, as investors await Nvidia's results after the bell.

The chip designer's shares were marginally up in premarket trading. Options pricing shows traders anticipate a move of around 9.8% in Nvidia's shares on Thursday, a day after it reports earnings, data from analytics firm ORATS showed.

Any disappointment in Nvidia's results could hurt megacaps and other semiconductor stocks, which have led 2024's rally on the prospect of artificial intelligence integration boosting corporate profits.

"The chip giant is again expected to demonstrate that it's firing on all cylinders," said Susannah Streeter, head of money and markets, Hargreaves Lansdown.

"But a lot will also be riding on the outlook and guidance from the firm, with some uncertainty swirling about just how long it will be before the rapacious appetite for its products is sated."

Other chip stocks such as Qualcomm and Advanced Micro Devices also edged higher, as did megacaps including Apple, Microsoft and Alphabet .

At 07:19 a.m., Dow E-minis were up 1 point, or flat, S&P 500 E-minis were up 0.25 point, or flat, Nasdaq 100 E-minis were down 2.25 points, or 0.01%.

Optimism continued to prevail that the U.S. Federal Reserve will lower interest rates at its September meeting after Fed Chair Jerome Powell's support for imminent policy adjustment last week, that had sparked broad-based market gains.

Odds of a 25-basis point reduction currently stand at 65.5%, while those of a 50-bps cut are at 34.5%, according to the CME Group's FedWatch Tool.

The Personal Consumption Expenditure report for July, due on Friday, is expected to provide further insight into the pace and magnitude of the central bank's rate-cut trajectory.

Comments on the economic outlook from voting member and Atlanta Fed President Raphael Bostic, due later in the day, will also be closely watched.

SentinelOne raised its annual revenue forecast, sending the cybersecurity company's shares up 1.9%.

Nordstrom jumped 4.6% after the department-store chain reported second-quarter profit which topped estimates, while Foot Locker sank 7% after the athletic apparel retailer posted a bigger quarterly loss.

(Reporting by Johann M Cherian and Purvi Agarwal in Bengaluru; Editing by Pooja Desai and Shounak Dasgupta)