Pony AI Inc (PONY) experienced a rollercoaster trading day on Tuesday, culminating in a 5.02% plunge during after-hours trading. This downturn came on the heels of a significant 42% intraday surge, driven by the announcement of a strategic partnership with Uber Technologies (UBER) to deploy Pony AI's robotaxis onto the Uber platform.

The partnership news, revealed in pre-market trading, initially propelled Pony AI's stock, with shares jumping 7% in early trading. The enthusiasm continued throughout the day, with trading volume surging to more than 44 million shares, compared to the daily average of about 5.53 million. The partnership is expected to first launch in a key market in the Middle East later this year, signaling a potentially lucrative expansion for Pony AI's autonomous mobility technology.

However, the after-hours plunge suggests a classic "sell the news" scenario or profit-taking by investors following the substantial intraday gains. Despite the positive partnership announcement, some investors may have decided to lock in profits, leading to the sharp reversal in stock price. This volatility underscores the speculative nature of the autonomous vehicle sector and the market's sometimes counterintuitive reactions to seemingly positive developments.