Overview
On-demand usage is a pay-as-you-go option for all AI features in Heptabase. Once your free credits and included plan credits are used up, you can enable on-demand usage to keep using AI features and pay based on actual usage.
How do I enable it?
Go to Settings → AI features and enable on-demand usage. You will then be asked to set a monthly spending limit, which officially activates it.
How does billing work?
On-demand usage is billed based on actual usage. It is not a prepaid package of credits. You do not buy a fixed batch of extra credits in advance. Instead, you use AI first and are charged afterward based on what you actually used.
Billing is triggered in two situations:
your running on-demand total reaches $10, or
your billing cycle ends, at which point any remaining unpaid usage is charged.
When the $10 threshold is crossed, the AI interaction that pushes you over generates an immediate bill for the running total at that moment (≈ $10) and charges you right then. Your counter then resets to $0, and the same rule applies again from there — the next charge is either when it hits $10 again, or whenever the cycle ends.
Example: your reset day is the 20th, and you start using on-demand on the 12th.
Scenario A — under $10 by cycle end: by the 20th, you've used $8.50 in total. You're charged $8.50 on the 20th when the cycle resets.
Scenario B — crosses $10 mid-cycle: on, say, the 16th, an AI interaction pushes your running total just past $10. That interaction itself triggers an immediate bill for ≈ $10 and your counter resets to $0. You keep using AI from the 16th to the 20th and accumulate, say, another $2.50. That $2.50 is then charged on the 20th with the cycle reset.
What does the monthly spending limit do?
The monthly spending limit caps your additional on-demand charges for the month.
For example, if your limit is set to $10, your pay-as-you-go charges for that month will stay at or close to $10.
Note: an AI interaction that crosses your spending limit will still complete, so the final charge may go slightly above the cap. After that point, on-demand usage is paused until your next billing cycle.
Does on-demand usage expire each month?
No. On-demand usage is not a monthly bundle that needs to be used up. It is simply pay-as-you-go billing for additional AI usage. You are charged only for what you use, up to your monthly spending limit.
Can I top up extra credits in advance?
No. On-demand usage is not a prepaid credit pack — there is no way to buy a bundle of credits ahead of time. You only pay for what you actually use, up to your monthly spending limit.
Will Basic models in the AI agent consume on-demand usage after my plan credits run out?
No. On Premium and Premium+, you can keep using Basic models (currently Gemini 3 Flash, GPT-5.4 mini and GPT-5.6 Luna) in the AI agent after your plan credits run out, and this stays free — it won’t consume on-demand usage even when on-demand is enabled. In this mode, the agent can read, search, and answer, but can’t create or edit content. On-demand billing applies to your other AI usage, such as premium models or AI Tutor.
Do unused monthly plan credits carry over to next month?
No. Plan-included credits reset on each billing cycle and do not accumulate. For more on how plan credits work, see Pro, Premium and Premium+ Plans: Pricing & FAQ.