What and why

You may be tempted to purchase(or are unable to afford) the $20/month subscription for ChatGPT plus. However, depending on the range of your usage and frequency of usage, it may not be so good of a deal compared to what you can just get from the API, which is pay-per-use.

The OpenAI API(OpenAI Platform) is intended for usage of developers, who may want to add the term "AI" to their products with no actual improvements to user experience but makes brand sound better somehow. With that being said, you do not need to know how to code to use most of the OpenAI API - the developer platform fortunately provides a playground where you can use it as if it is ChatGPT, with some additional settings you can tweak.

Pricing

Instead of paying a set $20/month, how much it costs depends on your usage. Basic models such as gpt4o/gpt3/gpt4 will likely cost you less than a cent per run. More heavy models such as o1 and gpt4.5 are likely to cost you about 10 cents per run. This is my estimate for the models' response to a simple question (e.g. "what is xxx") - asking it for more complex tasks may, obviously, cost more.

Limits

It may seem like that if you intend to mainly use the heavier models, $20/month may be a better option for you, assuming your API usage will go that much. However, even paid accounts can have limits on how many times a model can be used per day(for the heavy duty ones), and unfortunately, OpenAI doesn't exactly make their limits for ChatGPT users clear. Their limits are dynamically adjusted to fit their needs, hence you can really only figure out the limit when they tell you so. The API on the other hand is subject to their rate limits and how much you have in your wallet.

The fun part

Using the API doesn't mean you need to stop using your free account - in fact you should be using that first. Assuming you are a student that needs to upload pictures to ChatGPT 10-15 times a day, always use your free daily uses on ChatGPT, then switch over to the API for any additional uses. You are then on a pay per use basis for any usage outside of your free access.

Caveats

Not everything available in ChatGPT can translate 1:1 over to the API. Below is a table of what's available(and not) and possible replacements.

ChatGPT Features	OpenAI API
Memory	❓Kinda?*
Custom Instructions	❓Kinda?*
Web Browsing	✅Yes
GPTs	❓Kinda?
Reading image and audio	✅Yes
Reading other files	✅Yes**
Voice	✅Yes
Advanced Voice(video etc.)	❌No
DALL·E	❌No
Sora	❌No

*You can preset them in system instructions. Or upload them in a file and ask it to explicitly go over it if you would like it to understand your entire life up to their point.

**You can't just drag it in like you would in ChatGPT. See below.

Math Equations

The AI agents will write math equations in LaTeX, which the platform does not render. You may then need to paste the output into a markdown editor(such as Obsidian) and modify the equations so that they can be rendered. For example:

A linear transformation is a function between two vector spaces that preserves two operations:

• Addition: ( T(\mathbf{u} + \mathbf{v}) = T(\mathbf{u}) + T(\mathbf{v}) )
• Scalar multiplication: ( T(c\mathbf{v}) = cT(\mathbf{v}) ) for any vectors ( \mathbf{u}, \mathbf{v} ) and any scalar ( c ).

For inline equations like these, you will have to figure out where they start and end, and append a $ to both ends of the equation, like so:

• Addition: ( $\T(\mathbf{u} + \mathbf{v}) = T(\mathbf{u}) + T(\mathbf{v})$ )

You may also encounter full-line equations as follows:

[
T\left(\begin{pmatrix} x \ y \end{pmatrix}\right) = \begin{pmatrix} -y \ x \end{pmatrix}
]

Simply swap the brackets out for $$.

$$
T\left(\begin{pmatrix} x \ y \end{pmatrix}\right) = \begin{pmatrix} -y \ x \end{pmatrix}
$$

Once you make the change and paste it into an editor, you should be able to see the math equations.

Features

Web Browsing

This is only available in the prompts tab, not for assistants.

You will need to manually enable this feature. Go to tools - create and add web search in settings then fill it out(or not).

Reading non-image/audio files

Although images or audio can be used as if it were part of the text input, reading documents is an external feature just like web browsing. In either prompts or assistants, go to tools - file search then drag your document in. Then just ask it like normal(you may need to explicitly ask it to search the file).

GPTs

You can't access GPTs that others have created for ChatGPT. You can however use assistants to create a GPTs-like experience, where you can create multiple presets(simlar to prompts) of agents, each with different settings and system messages. The platform also provides a way to better phrase your responses with AI in the editor(for free !!).

Code Interpreter

(I didn't list this one in the table because I'm poor and not sure if ChatGPT+ actually offers this)

You can access this via Assistants and enabling it in tools.