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April 29 (Reuters) - U.S. stock index futures were mixed on Wednesday, in a cautious start to a day packed with several Big Tech earnings reports and a Federal Reserve meeting expected to be Chair Jerome Powell's last.

At 5:06 a.m. ET, Nasdaq 100 E-minis NQcv1 were up 73.25 points, or 0.27%, S&P 500 E-minis EScv1 gained 1.5 points, or 0.02%, and Dow E-minis YMcv1 rose 3 points, or 0.01%.

Amazon AMZN.O, Meta Platforms META.O, Microsoft MSFT.O and Google-parent Alphabet GOOGL.O are slated to report after the closing bell, when investors will gauge how their AI bets are paying off.

Sentiment has been slightly dampened heading into the earnings season, after a Wall Street Journal report said OpenAI had missed its internal targets for weekly users and revenue, reviving fears about the AI spending spree of tech heavyweights.

"After such a face-ripping rally in U.S. tech stocks, which has been the primary driver of Wall Street's recovery and record highs, doubts about returns and valuations have re-emerged," said Kyle Rodda, senior financial market analyst at Capital.com.

The OpenAI report could also give investors a "convenient cover" to sell and book profits in some outperformers, he added.

Amazon and Meta were flat in premarket trading, while Alphabet and Microsoft dipped 0.2% each.

POWELL'S CURTAIN CALL?

Investors will also tune into what could be Fed Chair Jerome Powell's final press conference as the head of the U.S. central bank.

Republican Senator Thom Tillis dropped his objection to the Senate confirmation of ​Kevin Warsh, who President Donald Trump had nominated to succeed Powell, after the Department of ​Justice ended ​an investigation ⁠into Powell that Tillis felt was a threat ​to the Fed's independence.

Traders expect the central bank to leave rates unchanged, but will closely parse Powell's remarks.

The Fed has previously said it is monitoring risks tied to the conflict, and with tensions in the Middle East showing few signs of easing, some investors worry policymakers may have to factor them more heavily into their outlook.

"While Powell's signals may be taken with some caution, given that this should be his last press conference, the risks are that he errs on the hawkish side," wrote ING Economics' FX strategist Francesco Pesole.

Iran's latest proposal for ending the two-month war would set aside discussion of its nuclear program until the conflict was concluded and shipping disputes resolved. Trump, however, said he was unhappy with the offer.

Meanwhile, major movers in the premarket session include online brokerage Robinhood Markets HOOD.O, which fell 10% after missing expectations for first-quarter profit.

NXP Semiconductors NXPI.O rose 16.1% after it forecast second-quarter revenue and profit above Wall Street expectations.