How are messages priced?

Credits are charged per message, and the price depends on the model: the model picker shows it ("1 credit per message", for example) and about how many messages your credits pay for. Very large messages, such as ones with big files or long chats, can cost more, and the message box tells you when that happens.

Web searches add a small number of credits per search. While an answer is being written its credits are held, then the actual amount is charged when it finishes. When you’re low on credits, the answer is kept short enough to fit what you have, so you never owe anything.