If you're even a moderate user of chatGPT, the equivalent cost of using the smallest GPT4 model would run you a
hell of a lot more. Let's actually run the numbers.
The cost of the GPT-4 API is ballpark around $0.05 / 1000 tokens. If you want to include a rolling context window, you will easily hit 1000+ tokens if not a huge amount more.
ChatGPT pro gives you 50 GPT-4 queries every three hours. If you're using it all day you might average about 100 daily queries. Using a dedicated GPT4 API would run you approximately five dollars a day for the same thing - that's $150 a month as opposed to flat cost of $20.
How hard is it to hit 100 queries in a day? Pretty damn easy when you realize that most queries aren't usually standalone - instead they involve a back and forth approach which necessitates a rolling context window and you explore the problem space.
When a query (plus back and forth) might cost as much as $0.25, paying for GPT-4 via the API would only net you a whopping 80-100 queries per month before you exceeded the cost of a pro subscription.
The API certainly has its advantages over the web based ChatGPT, but price is definitely not one of them.