What a 24/7 AI Agent Actually Costs: API vs Subscription
A 30-day worked scenario at three volumes: $239 to $7,155 a month on metered GPT-5 pricing, against flat ChatGPT plan setups at $149 to $329. Estimates, math shown.
An always-on agent costs between roughly $240 and $7,200 a month at June 2026 GPT-5 API rates, depending on volume. The same three workloads run flat at $149 to $329 a month on ChatGPT plans through a subscription-backed endpoint, using capacity estimates rather than guarantees. Here is the 30-day arithmetic at three volumes, both ways.
The reference agent
To make the numbers honest, fix the shape first. Our reference 24/7 agent (monitoring, triage, scheduled jobs, event-driven tasks) averages:
- 12 model calls per task
- 5,000 input / 700 output tokens per call, so 60,000 input and 8,400 output tokens per task
- GPT-5 at $1.25 input / $10 output per million tokens (June 2026, live prices at openai.com/api/pricing)
Per task: 0.06 x $1.25 + 0.0084 x $10 = $0.075 + $0.084 = $0.159. If your agent is shaped differently, the formula to rebuild this table is in how to calculate AI agent costs.
The 30-day API arithmetic
| Volume | Tasks/day | Monthly tokens (in / out) | GPT-5 API cost |
|---|---|---|---|
| Light | 50 | 90M / 12.6M | $238.50 |
| Medium | 300 | 540M / 75.6M | $1,431 |
| Heavy | 1,500 | 2.7B / 378M | $7,155 |
Checking the medium row by hand: 9,000 tasks x 60k input = 540M input tokens, which is 540 x $1.25 = $675. Output is 9,000 x 8.4k = 75.6M tokens, which is 75.6 x $10 = $756. Total $1,431 a month, every month, for as long as the agent runs.
Model choice moves the whole table: on GPT-5.5 ($5/$30) multiply by roughly 3.5x, on GPT-5 Mini ($0.25/$2) divide by 5. Prompt caching and batch discounts shave the metered number but never change its shape: it scales with every task the agent takes on.
The subscription math
ChatGPT plans include Codex, and Codex Hosted runs OpenAI’s official Codex CLI signed into your own account, exposed as an OpenAI-compatible endpoint. The workload then bills against the flat plan instead of the meter. Our planning estimates for plan capacity: Plus ($20) absorbs roughly $700 of API-equivalent work a month, Pro 5x ($100) roughly $3,500, Pro 20x ($200) roughly $14,000. These are estimates from observed usage windows; OpenAI adjusts limits over time.
| Volume | API cost | Covering setup | Flat cost | Monthly difference |
|---|---|---|---|---|
| Light | $238.50 | Plus + ProxyLLM | $20 + $129 = $149 | ~$90 |
| Medium | $1,431 | Pro 5x + ProxyLLM | $100 + $129 = $229 | ~$1,200 |
| Heavy | $7,155 | Pro 20x + ProxyLLM | $200 + $129 = $329 | ~$6,800 |
At medium volume, the same 24/7 agent costs $1,431 on the meter and about $229 against a Pro plan. The $129 is our flat SaaS fee; we add no inference markup, so the flat cost does not grow with task count. Five more scenarios with full tables are in Codex Hosted savings examples.
Why always-on agents suit usage windows
A 24/7 agent is the friendliest workload a usage window will ever see: steady draw around the clock, no burst that slams a window in an afternoon. Bursty workloads (a launch-day backfill, a batch migration) are the ones that exhaust windows early.
The honest caveats, so the flat number stays trustworthy:
- Windows, not budgets. Capacity arrives in rolling windows. A heavy day can exhaust one early; requests then fall back to a second connected account, then to your own API key until the reset. The mechanics are in what happens when you hit the Codex usage limit.
- Complete responses on the Codex lane. No token streaming; the response arrives whole. Background agents do not care. A live chat UI does, so keep that on the API lane.
- Estimates are estimates. Size against the middle of the capacity range. If your metered bill sits near a tier’s ceiling, plan for the next tier or a second account ($100 steps, not linear growth).
- Programmatic Codex use is documented OpenAI functionality, but OpenAI has the final call on its accounts and services.
What moves your number
Four inputs dominate: tasks per day (linear), calls per task (linear, and the easiest to trim), model choice (5x to 20x swings), and retry rate (a silent 10 to 25% tax). Get those four from a week of logs and the 30-day projection is usually within 15%.
Put your own volumes into the calculator; it runs this table for your numbers and picks the covering tier, including multi-account setups past Pro 20x.
Frequently asked questions
How much does it cost to run an AI agent 24/7?
At June 2026 GPT-5 API rates, a light always-on agent (50 tasks/day) costs about $239 a month, a medium one (300 tasks/day) about $1,431, and a heavy one (1,500 tasks/day) about $7,155. The same workloads map to flat subscription-backed setups at roughly $149, $229, and $329 a month, based on capacity estimates.
Is the API or a ChatGPT subscription cheaper for an always-on agent?
Below roughly $150 a month of API spend, stay on the meter. Above it, a ChatGPT plan run through Codex Hosted is cheaper: a medium-volume 24/7 agent costs about $1,431 metered versus about $229 flat. Plan capacity figures are estimates from observed usage windows, not guarantees.
What happens when a 24/7 agent hits the plan's usage limit?
Plan capacity arrives in rolling windows. When a window is exhausted, requests fall back to a second connected ChatGPT account, then to your own OpenAI API key until the window resets, so the agent keeps running and the request log shows which lane served each call.
Are the plan capacity numbers guaranteed?
No. Plus at roughly $700, Pro 5x at roughly $3,500, and Pro 20x at roughly $14,000 of API-equivalent work per month are planning estimates derived from observed usage windows. OpenAI publishes and adjusts limits on its pricing page, so size against the middle of the range, not the top.