ORLANDO, Florida, July 27 (Reuters) - Oil prices tumbled on Monday as the U.S. and Iran swapped attacks on each other for dialogue, while Wall Street and Treasuries traded in much narrower ranges as investors looked ahead to a raft of big tech earnings reports and the Federal Reserve's policy decision later this week.

In my column today, I look ahead to the Fed meeting. If Chair Kevin Warsh wants to cement - or restore? - the central bank's inflation-fighting credibility, the Fed should probably raise rates. But markets are only putting a one-in-three probability on a move. Can the Fed afford to surprise markets? Can it afford not to?

If you have more time to read, here are a few articles I recommend to help you make sense of what happened in markets today.

1. Chipmaker CXMT vaults to top of China's valuation with 466% surge in Shanghai debut

2. Nvidia in talks with OpenAI to guarantee $250 billion financing for data center, WSJ reports

3. Trump economy at 18 months is a tale of shocks, resilience, and signs of stalled progress

4. Bank of England to keep rate steady despite oil and gas price rebound

5. Bank of Japan to signal more rate hikes as price pressures build

Today's Key Market Moves

-- STOCKS: China's benchmark indices up 1-3%; Europe flat, UK +0.4%; Dow +0.5%, S&P 500 and Nasdaq little changed.

-- SECTORS/SHARES: Seven sectors on the S&P 500 rise, four fall. Comms services and consumer staples +1.5%, energy -2%, tech -1%. Workday +9%, Palantir +7%, Sandisk -11%, Nvidia -5%.

-- FX: Dollar index flat. NOK down almost 1% on oil slide, IDR slides on cenbank chief exit. INR logs best day in six weeks.

-- BONDS: U.S. yields down 1-4 bps, curve bull flattens a bit. 2-year auction pretty soft, 5-year auction very weak.

-- COMMODITIES/METALS: Oil tumbles: WTI crude -7.5%, Brent -9%. Gold +1%.

Today's Talking Points

* AI froth

With equity investors already on edge ahead of a huge earnings week for Big Tech globally, they got a reminder on Monday of how frothy AI sentiment still is, even after the recent tech selloff. Shares of Chinese chipmaker CXMT Corp soared more than 500% on their trading debut on Monday following Asia's biggest IPO this year, making it China's most valuable listed company.

Meanwhile, the WSJ reports that Nvidia is in talks to provide $250 billion in financing guarantees for OpenAI as part of a massive data center project, with total costs including chips financing potentially well over $500 billion - eye-watering numbers, and yet more circular financing. The bar for this week's U.S. and South Korean megacap earnings is getting higher.

* Fed (in)visibility

Could the Fed surprise markets with a rate hike on Wednesday? It's certainly possible, although it wouldn't come as a complete shock - on Monday, fed funds futures pricing of a quarter-point hike reached 40% at one point. That's eased back to around 35%, which is still remarkably high only 48 hours away from the decision.

Based on market pricing, analysts at HSBC calculate that Wednesday's decision is the most uncertain in two years and one of the least certain in over four years. As they note, in the era of forward guidance, uncertainty so close to an FOMC meeting is unusual. But new Fed Chair Warsh has consigned forward guidance to history. Maybe this lack of visibility is the new normal.

* Bonds ignore oil

Benchmark global oil prices sank between 7% and 9% on Monday, their biggest fall in over two months. From Thursday's peak to today's trough, WTI fell as much as 12%. Yet the decline in Treasury yields has been very modest - the 10-year closed on Monday at 4.64%, only 7 bps off last week's peak above 4.71%.

The bond market is signaling it doesn't put much faith in the latest U.S.-Iran detente lasting, or even if it does, inflationary pressures are unlikely to cool much. It's the early innings, but the economy is moving into an era of structurally higher yields, certainly relative to the last decade. The 30-year yield is in its longest stretch above 5% since 2007. Businesses and households will have to adjust. Investors too.

What could move markets tomorrow?

-- SK Hynix earnings

-- European earnings, including Barclays and Unilever

-- U.S. consumer confidence (July)

-- U.S. Treasury sells $44 billion of 7-year notes at auction

-- U.S. earnings, including Visa, Coca-Cola, Boeing, Seagate Technology

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