The biggest US tech companies have led a spectacular rebound in the stock market, but their recent earnings indicate tech isn’t a surefire bet.  Alphabet (Google), Amazon, Apple all report earnings on Thursday.

Spotify, Facebook, PayPal and Qualcomm all report Wednesday. (Netflix, one of the FAANG stocks, the others being Facebook, Amazon, Apple, Google, has already reported. So too has Microsoft.)

Shares of Intel plunged on Friday after the company said its next-generation chips will be delayed, while Snap’s stock fell after the company noted that a spike in users of the app after the pandemic began was tapering off.

That sets the scene for a momentous earnings week in Silicon Valley, with results due from Amazon, Apple, Alphabet and Facebook. The massive run-up in these companies’ shares — and questions about whether they’re overvalued — means investors will be particularly attuned.

Facebook, Amazon, Apple, Alphabet and Microsoft, the five largest US companies, now account for more than one fifth of the value of the S&P 500, up from 16% a year ago, Goldman Sachs said in a recent note to clients.

These stocks have returned roughly 35% this year, while the 495 other stocks in the index have lost 5%, per the investment bank.

Bulls are quick to point out that shares of these companies are rising because their businesses are strong, with profits at least partially insulated from the Covid-19 shock.

There’s a lot riding on that view.

“Record concentration means the S&P 500 has never been more dependent on the continued strength of its largest constituents or more vulnerable to an idiosyncratic shock to any of these stocks,” Goldman Sachs’ chief US equity strategist David Kostin wrote.

One example: Apple’s shares have shot up 26% in 2020, in part due to anticipation about the release of new 5G phones this fall. But there’s growing chatter that the timeline could be pushed back.

Deutsche Bank analysts said in a note last Thursday that they are increasingly confident that new iPhone launches will be delayed to November or December amid technical complications tied to coronavirus. That may not affect profits over the long run, but could jolt the confidence of investors.

Just how bad was the hit to the US economy this spring?

How hard did the pandemic hit the US economy between April and June?

Investors will find out this week, providing crucial data on how strong the recovery must be to propel the world’s largest economy out of a historic recession.

Economists surveyed by Refinitiv on average expect to learn that US output shrank at an annualized rate of 34% last quarter. That’s almost triple the peak-to-trough contraction recorded during the Great Recession, Bank of America pointed out in a recent note to clients.

“This is a consumer-led downturn, but we are likely to see substantial drags across all major GDP components,” its US economist Alexander Lin said.

Amid a fast-moving health crisis, it’s tempting to frame the second quarter data as already obsolete. But the information is crucial, both for economists trying to assess how big a bounce back is needed and for policymakers in Congress racing to approve additional stimulus measures targeting the economy’s weak spots.