• AI company Anthropic debuted a powerful artificial intelligence model.
• Gilead's twice-yearly shot to prevent HIV succeeded in a late-stage trial.
• Amazon has replaced most of its plastic fillers with paper in North America.

Here are five key things investors need to know to start the trading day:

1. Winning week so far

The S&P 500 briefly passed the 5,500 level for the first time on Thursday before pulling back. The broad market index closed down 0.25% while the Nasdaq Composite dropped 0.79%. The Dow Jones Industrial Average, meanwhile, rose 299.90 points, or 0.77%, good for its best day this month. Despite turning negative on Thursday, stocks are headed for a winning week, with the S&P 500 and Nasdaq notching new records earlier in the week. Follow live market updates.

2. AI's still hot

This spring saw a surge of new AI technology, and the official start to summer is shaping up to be no different. AI company Anthropic debuted its most powerful artificial intelligence model on Thursday. The OpenAI competitor announced Claude 3.5 Sonnet, saying it was faster than its previous leading model. Claude is a chatbot like OpenAI's ChatGPT and Google's Gemini, and all three companies have seen the technology explode in popularity in the past year. Anthropic also announced a tool called "Artifacts" that it said will be useful for code development, legal contract drafting and analysis, business report writing and more.

3. HIV shot

Biopharmaceutical company Gilead said its experimental shot to prevent HIV was 100% effective in a late-stage trial. The lenacapavir shot, if approved, would be administered twice yearly and would be a longer-acting option that could reach people who can't or don't want to take a daily pill. Gilead needs to replicate the results in another Phase 3 trial before seeking FDA approval. If that trial goes well, the company could bring the shot to market as soon as late 2025. Shares of the company rose about 8.5% and notched their best day since 2022.

4. Some hard truth

Shares of Trump Media — the company behind conservative social media site Truth Social, which is majority-owned by former President Donald Trump — fell roughly 15% on Thursday, deepening a sell-off for the stock. The stock saw massive trading volume for the day, as more than 13.2 million shares of Trump Media changed hands — over three times its 30-day average trading volume. Meanwhile, Trump's shares of DJT have fallen from a value of more than $5.6 billion at the beginning of the month to roughly $3 billion after Thursday's close. Thursday's losses follow the company saying the SEC had declared its registration statement effective, allowing early investors in the company to resell certain shares and exercise stock warrants. Trump Media stock has slumped since May 30, when a New York jury convicted the former president on 34 felony counts of falsifying business records.

5. Bagging it

Paper beats plastic. Amazon said Thursday that it has removed 95% of plastic air pillows in North America, its largest plastic-packaging reduction effort yet. The company is replacing them with paper fillers made from 100% recycled content. It began transitioning away from plastic fillers in October when it announced its first U.S. automated fulfillment center to eliminate plastic-delivery packaging.

— CNBC's Samantha Subin, Hayden Field, Angelica Peebles, Kevin Breuninger and Katie Bartlett contributed to this report.

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