As a Plus subscriber, I asked GPT4 what is the maximum input size yesterday and today. To my big surprise, the limit went down from 8192 to 4096 tokens.
Note that this is the limit of web version at https://chat.openai.com and not the API.
Yesterday's response: https://chat.openai.com/share/dd8f00db-1ddc-4af0-9a6a-7254e301c4b2
The input character limit for this version of GPT (GPT-4) is 8,192 tokens. Keep in mind that tokens can be parts of words, whole words, or several words, depending on the language and context.
Today: https://chat.openai.com/share/6d2e6753-d15e-4e40-b44b-0582d33953ce
The input size for GPT (including this version, GPT-4) is 4096 tokens. This includes both the prompt and the system's response. Each token can be a word or part of a word, so the actual number of words you can input will vary, but it's usually around 1500-2000 words depending on the complexity and length of the words.