How Much Does It Cost to Run a Coding Agent on GPT-6?
I ran the numbers on my own setup last week and the answer annoyed me: there isn't one. A coding agent's API bill is a function of your workload — repo size, how many tasks you throw at it, how much context it drags along, how many iterations it takes to land a diff. Any article that hands you a single "typical" number is inventing data.
So here's the honest version of this article: given workload X, the API cost is Y. Below are three illustrative scenarios, every number computed from official OpenAI pricing through our pricing data layer. Find the scenario closest to your setup — or better, hit the button under it and replace X with your own workload.
A note on these scenarios. These are illustrative workload scenarios, not estimates of typical coding-agent usage. Actual token usage varies substantially by repository size, context length, tool calls, iteration count, caching, and agent behavior. We don't have reliable industry-average data, and we won't invent any.
The three scenarios
Each scenario assumes 22 workdays per month. Token counts are per task; the calculator links below pre-fill the exact same numbers so you can tweak from there.
Light The weekend tinkerer
Assumptions: 10 tasks/day · 20K fresh + 40K cached input + 5K output tokens per task · 220 tasks/month. Small repo, quick fixes, tight loops.
Medium The daily driver
Assumptions: 20 tasks/day · 50K fresh + 150K cached input + 20K output tokens per task · 440 tasks/month. Mid-size repo, feature work, a few retries per task.
Heavy The fleet operator
Assumptions: 30 tasks/day · 100K fresh + 400K cached input + 50K output tokens per task · 660 tasks/month. Large monorepo, long agentic loops, agents running in parallel.
Monthly cost by scenario (GPT-6 Sol)
Same workload, different model
Hold the Medium scenario fixed and swap the model. This is where model choice dwarfs workload tuning:
| Model | Per task | Per month |
|---|---|---|
| GPT-6 Luna | $0.02 | $7.26 |
| GPT-6 Sol | $0.33 | $145.20 |
| Claude Opus 5.5 | $0.63 | $277.20 |
| GPT-6 Astra | $1.65 | $726.00 |
Luna is cheapest on paper ($7.26/month) but it's the budget generalist, not the coding specialist. Sol is the one built for this job, and it's still 1.91× cheaper than Claude Opus 5.5 ($132/month less) on the same workload. Astra is a 100×-Luna-priced flagship; running a coding agent on it is lighting money on fire. The full head-to-head is in our GPT-6 vs Claude cost comparison.
Caching is the real lever
Coding agents re-read the same files constantly — system prompts, repo context, conversation history. That's exactly what prompt caching discounts. On the Medium scenario with GPT-6 Sol:
| Cached input share | Per month |
|---|---|
| 0% (caching off) | $264.00 |
| 75% | $145.20 |
Going from 0% to 75% cached saves $118.80/month — 45%. That's a bigger swing than switching models, and it costs you nothing but keeping your agent's context stable. More tactics in our GPT-6 cost-saving tips.
Your workload, your number
None of these scenarios is you. Plug in your actual tasks-per-day, context size, and cache share — it takes 30 seconds.
Open the GPT-6 Sol Cost CalculatorOfficial OpenAI pricing · Last verified September 26, 2026
FAQ
Why don't you just give one number for coding-agent cost?
Because token usage varies too much to be captured by one number — it depends on repository size, context length, tool calls, iteration count, caching, and agent behavior. We publish three illustrative scenarios instead of a fake average, and every figure is computed from official pricing.
Which GPT-6 model is best for coding agents?
GPT-6 Sol — it's the coding specialist. On the Medium scenario it costs $0.33 per task ($145.20/month), 1.91× less than Claude Opus 5.5 on the same workload.
How does prompt caching affect coding-agent costs?
Dramatically. On the Medium scenario, 75% cached input costs $145.20/month versus $264.00/month with caching off — a 45% saving ($118.80).
Is Claude Opus 5.5 cheaper than GPT-6 Sol for coding agents?
No. On the same Medium workload, Opus 5.5 costs $277.20/month versus Sol's $145.20 — that's 1.91×, or $132 more per month.
Are the Light/Medium/Heavy scenarios typical usage?
No — they're illustrative reference points, not industry averages. We don't have reliable data on typical coding-agent usage and won't invent any. Use them to orient yourself, then measure your own workload.