GPT-5.6 Luna vs GPT-5.6 Terra
GPT-5.6 Luna was superseded by GPT-6 Luna. The grades below are the last ones measured, so read them as history rather than as this week's board. See the current roster.
Both grade D overall. GPT-5.6 Luna is the cheaper side per task (at most $0.012). By suite, GPT-5.6 Terra takes real-world issues (D+ to D) and GPT-5.6 Luna takes spec planning (C- to D+). Both agents run the same private suite cut headless through their own tools, each on its own subscription.Measured
Each agent graded on the same private suites, running headless through its own tools. Advantages are oriented so a win is a win, whichever way the metric runs.
Verdict: GPT-5.6 Terra vs GPT-5.6 Luna
Both grade D overall. By suite: GPT-5.6 Terra takes real-world issues, D+ to D (50% vs 45% capability); GPT-5.6 Luna takes spec planning, C- to D+ (57% vs 53% capability); vibe coding is even at F (25% vs 34% capability). GPT-5.6 Luna used <1% of ChatGPT Pro 5x's weekly limit per pass, at most $0.012 per task at the listed price. GPT-5.6 Terra used 8% of ChatGPT Plus's weekly limit per pass, $0.019 per task at the listed price; at the ~$100 tier the board defaults to that is an estimated ~1.6% of ChatGPT Pro 5x's weekly limit (est, about $0.019 per task). Per task, GPT-5.6 Luna costs at most $0.012 against GPT-5.6 Terra's $0.019, so GPT-5.6 Luna is the cheaper side. GPT-5.6 Terra is faster on real-world issues: a median task takes 2m 18s against 3m 7s. Both finished every task on it.
Changed since the previous graded week: GPT-5.6 Luna: spec planning D+ to C-, vibe coding C- to F; GPT-5.6 Terra: real-world issues D to D+, real-world issues usage 9.2% to 7% of the weekly limit, spec planning C- to D+, spec planning usage 2.0% to 1% of the weekly limit, vibe coding F to D, vibe coding usage 0.5% to 0.6% of the weekly limit.
| Dimension | GPT-5.6 Luna | GPT-5.6 Terra | Advantage |
|---|---|---|---|
| Capability | 45% | 50% | +5% (GPT-5.6 Terra leads) |
| Median task time | 3m 7s | 2m 18s | 49s faster (GPT-5.6 Terra leads) |
| Approx. task cost | <$0.015 / task | $0.021 / task | $0.006 / task lower (GPT-5.6 Luna leads) |
GPT-5.6 Luna: under 1% of ChatGPT Pro 5x per run. GPT-5.6 Terra: 7.0% of ChatGPT Plus (46.0% / 5h, 7.0% / 1w) per run. Its weekly limit holds about 6 of the week's 33.6 5h windows. Each figure is a share of that agent's own plan, so there is no delta to draw.
| Dimension | GPT-5.6 Luna | GPT-5.6 Terra | Advantage |
|---|---|---|---|
| Capability | 57% | 53% | +3% (GPT-5.6 Luna leads) |
| Median task time | 3m 25s | 2m 37s | 48s faster (GPT-5.6 Terra leads) |
| Approx. task cost | <$0.057 / task | $0.011 / task | $0.046 / task lower (GPT-5.6 Terra leads) |
GPT-5.6 Luna: under 1% of ChatGPT Pro 5x per run. GPT-5.6 Terra: 1.0% of ChatGPT Plus (10.0% / 5h, 1.0% / 1w) per run. Its weekly limit holds about 6 of the week's 33.6 5h windows. Each figure is a share of that agent's own plan, so there is no delta to draw.
| Dimension | GPT-5.6 Luna | GPT-5.6 Terra | Advantage |
|---|---|---|---|
| Capability | 25% | 34% | +9% (GPT-5.6 Terra leads) |
| Median task time | 3m 40s | 2m 47s | 53s faster (GPT-5.6 Terra leads) |
| Approx. task cost | <$0.230 / task | $0.028 / task | $0.202 / task lower (GPT-5.6 Terra leads) |
GPT-5.6 Luna: under 1% of ChatGPT Pro 5x per good solve. GPT-5.6 Terra: 0.6% of ChatGPT Plus (3.0% / 5h, 0.6% / 1w) per good solve. Its weekly limit holds about 6 of the week's 33.6 5h windows. Each figure is a share of that agent's own plan, so there is no delta to draw.
Grades and deltas are comparable only within a suite version. See methodology.
Frequently asked questions
Which is better for coding, GPT-5.6 Luna or GPT-5.6 Terra?
GPT-5.6 Terra clears higher: tier 2 of 5 versus tier 1 for GPT-5.6 Luna on real-world@v3, our private suite of real-world coding problems. Latest measurement 2026-09-21.
Which is cheaper per task, GPT-5.6 Luna or GPT-5.6 Terra?
GPT-5.6 Luna used <1% of ChatGPT Pro 5x's weekly limit per pass, at most $0.012 per task at the listed price. GPT-5.6 Terra used 8% of ChatGPT Plus's weekly limit per pass, $0.019 per task at the listed price; at the ~$100 tier the board defaults to that is an estimated ~1.6% of ChatGPT Pro 5x's weekly limit (est, about $0.019 per task). Per task, GPT-5.6 Luna costs at most $0.012 against GPT-5.6 Terra's $0.019, so GPT-5.6 Luna is the cheaper side.
What do GPT-5.6 Luna and GPT-5.6 Terra cost a month?
GPT-5.6 Luna runs on ChatGPT Pro 5x at $100/month (public price as of 2026-09-05). GPT-5.6 Terra runs on ChatGPT Plus at $20/month (public price as of 2026-07-20).