Standard Compute
Cost per coding-agent request

Is GPT-5.5 or GPT-5.6 Luna cheaper for coding agents?

For coding agents, GPT-5.5 costs 25x as much as GPT-5.6 Luna per request ($0.21 vs $0.0084 on our measured traffic), because GPT-5.5 lists at $5 input, $0.50 cached input and $30 output per million tokens against $0.20, $0.02 and $1.20 for GPT-5.6 Luna, and both charge more for long prompts.

List prices: OpenAI API pricing, checked 2026-10-13. Request costs: Standard Compute gateway data, 79,301 coding-agent requests from 75 users, Sep 13 to Oct 12, 2026. How we compute this

Run GPT-5.6 Luna and GPT-6 Luna in your agent from $19/month

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Cost per coding-agent request, side by side

Cost at list priceGPT-5.6 LunaGPT-5.5
Prompt under 100K tokens50% of requests, 87% of input cached$0.0032$0.081
Prompt of 100K to 272K39% of requests, 88% of input cached$0.0080$0.20
Prompt over 272K tokens11% of requests, 86% of input cached$0.034$0.86
Average request$0.0084$0.21
100 requests$0.84$20.99
Median session16 requests; a session ends after 10 idle minutes$0.092$2.30
A month of regular usemedian of 20 users active on 5+ days$11.83$296

Each logged request priced at the vendor’s list rates for its own token counts, including cache reads and any higher rate for long prompts. Average output: 698 tokens per request.

Benchmarks, speed and latency, side by side

Artificial AnalysisGPT-5.6 LunaGPT-5.5
Intelligence Index10 evaluations, 0 to 1003738
Terminal-Bench 4.0agentic coding in a terminal11.6%14.6%
Output speedmedian123 tokens/s105 tokens/s
Time to first answer tokenincludes thinking time117 s71 s

Source: Artificial Analysis (artificialanalysis.ai). Measured variants: GPT-5.6 Luna (Max), speed on OpenAI; GPT-5.5 (Xhigh), speed on OpenAI. Fetched October 13, 2026. Artificial Analysis runs Terminal-Bench 4.0 in its own setup, so its scores differ from the tbench.ai leaderboard.

What to watch for

GPT-5.5 is superseded: GPT-6.1 Sol costs $0.067 per request. GPT-5.6 Luna is superseded: GPT-6 Luna costs $0.0041 per request. GPT-5.6 Luna scores close to it on the benchmarks above, so the cheaper request is not bought with much lower ability.

FAQ

Is GPT-5.6 Luna cheaper than GPT-5.5 for coding agents?
Yes, at list prices. 100 average coding-agent requests cost $0.84 on GPT-5.6 Luna and $20.99 on GPT-5.5. A median 16-request session costs $0.092 vs $2.30. Measured on 79,301 real coding-agent requests (Sep 13 to Oct 12, 2026).
How much does a month of GPT-5.5 vs GPT-5.6 Luna cost?
For the median regular user in our data (1,478 requests in 30 days), about $296 on GPT-5.5 and $11.83 on GPT-5.6 Luna at list price. Heavier users pay proportionally more.
GPT-5.5 vs GPT-5.6 Luna: which is better for agents?
GPT-5.5 scores higher on output quality (7.6/10 vs 7.4/10), while GPT-5.6 Luna is the cheaper option. GPT-5.5 is best for existing GPT-5.5 setups on an API key until they move to GPT-6.1 Sol; GPT-5.6 Luna is best for cheap subtasks in existing GPT-5.6 setups. Live community votes on this page show what people actually prefer.
Can I switch between GPT-5.5 and GPT-5.6 Luna in the same agent?
Yes. Model-agnostic agents (Cline, Aider, OpenClaw, Hermes Agent, Kilo Code, OpenCode) let you swap models per task. Many people route hard tasks to the stronger model and routine work to the cheaper one.

Community vote

Pick a winner in each dimension. You can change your vote any time. 17 votes cast so far.

Output Quality

Correctness and depth of what it produces

10%10 votes90%

Agentic Ability

Tool calls, instruction-following, and multi-step tasks

0%2 votes100%

Speed

Tokens per second and time-to-first-token

0%2 votes100%

Value for Money

How much capability you get per dollar

0%2 votes100%

Reliability

Consistent results: fewer refusals, loops and format breaks

100%1 vote0%

Related comparisons

Setting it up? GPT-5.6 Luna: model ID, providers and agent config

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