(Reuters) - AI startup OpenAI said on Thursday its chatbot ChatGPT now has more than 200 million weekly active users, double the number it had in the last fall season.

ChatGPT, launched in 2022, can generate human-like responses based on user prompts and had 100 million weekly active users, OpenAI CEO Sam Altman had said in November.

OpenAI said 92% of Fortune 500 companies are using its products and the use of its automated Application Programming Interface, or API, which allows software programs to talk to each other, has doubled since the launch of ChatGPT-4o mini in July.

GPT-4o mini is a cost-efficient small AI model, aimed at making its technology more affordable and less energy-intensive, allowing the startup to target a broader pool of customers.

ChatGPT has driven AI's popularity and fueled a meteoric rise in the valuation of the San Francisco-based OpenAI.

Separately, AI startups OpenAI and Anthropic signed deals with the U.S. government for research, testing and evaluation of their artificial intelligence models, the U.S. Artificial Intelligence Safety Institute said earlier in the day.

Media reports said Apple ( AAPL ) and Nvidia ( NVDA ) are in talks to invest in OpenAI as part of a new fundraising round that would value the ChatGPT maker above $100 billion.

OpenAI-backer Microsoft ( MSFT ) is also expected to invest in the firm, according to the reports.

(Reporting by Juby Babu in Mexico City; Editing by Arun Koyyur)