From Wikipedia,

Sputnik 1 was the first artificial Earth satellite. It was launched into an elliptical low Earth orbit by the USSR on 4 October 1957 as part of the Soviet space program. It orbited for three weeks before its batteries died and then orbited silently for two months before it fell back into the atmosphere on the 4th January 1958.

[...]

The satellite's unanticipated success precipitated the American Sputnik crisis and triggered the Space Race, part of the Cold War. The launch was the beginning of a new era of political, military, technological and scientific developments.

An "AI Sputnik moment" would, by contrast, be a sudden understanding by the general public that artificial intelligence is worth taking extremely seriously, perhaps triggering a similar AI arms race.

Will there be an AI Sputnik moment before 2050?

There is said to be an "AI Sputnik moment" if ANY of the following come true before 2050,

A major technology company (>50 billion dollar market cap, in 2021 US dollars, right before the announcement) announces the creation of an AI system. Upon the announcement, their stock price skyrockets by over 100% compared to its previous value within 7 days, and numerous highly credible media reports claim that this rise in stock price is likely a result of the AI development.
News of an AI development triggers the head of government of the top 2 nations by GDP nominal to give a public speech regarding the ramifications of this particular AI development, within two weeks of the initial news reports.
The Nasdaq Composite (which is currently heavily weighted towards companies in the information technology sector) rises over 30% in the course of a single week, and numerous highly credible media reports claim that this rise in stock prices is likely a result of the AI development.
The Google Trends monitor for artificial intelligence shows that interest in artificial intelligence rises by over 100% relative to of its previous value, compared to the week prior (using the resolution at 12 months, as currently displayed by the Google Trends widget). If Google Trends changes their functionality or methodology dramatically (as determined by Metaculus admins), then this condition can no longer trigger a positive resolution.
Practically all reliable media outlets are referring to an AI development as an AI Sputnik moment, as referring to the historical Sputnik 1 satellite.