GPT-5.6 Terra vs GPT-6 Luna
GPT-5.6 Terra leads overall, D+ to D. GPT-6 Luna is about 10x cheaper per task. By suite, real-world issues is even at D+ and GPT-5.6 Terra takes spec planning (C to C-). Take GPT-6 Luna anyway when you want the side that is cheaper per task and faster on real-world issues.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-6 Luna vs GPT-5.6 Terra
GPT-5.6 Terra leads overall, D+ to D. By suite: real-world issues is even at D+ (50% vs 50% capability); GPT-5.6 Terra takes spec planning, C to C- (68% vs 61% capability); vibe coding is even at F (34% vs 33% capability). GPT-5.6 Terra used 2% of ChatGPT Pro 5x's weekly limit per pass, $0.024 per task at the listed price. GPT-6 Luna used 1% of ChatGPT Plus's weekly limit per pass, $0.002 per task at the listed price; at the ~$100 tier the board defaults to that is an estimated ~0.2% of ChatGPT Pro 5x's weekly limit (est, about $0.002 per task). Per task, GPT-6 Luna is about 10x cheaper ($0.002 vs $0.024). GPT-6 Luna is faster on real-world issues: a median task takes 1m 0s against 3m 29s. Both finished every task on it. Reasons to pick GPT-6 Luna anyway: it is cheaper per task ($0.002 vs $0.024) and it is faster on real-world issues (1m 0s vs 3m 29s median).
Changed since W38: GPT-5.6 Terra: real-world issues usage 1% to 2% of the weekly limit, spec planning C- to C, vibe coding D- to F.
| Dimension | GPT-5.6 Terra | GPT-6 Luna | Advantage |
|---|---|---|---|
| Capability | 50% | 50% | Even |
| Median task time | 3m 29s | 1m 0s | 2m 29s faster (GPT-6 Luna leads) |
| Approx. task cost | $0.031 / task | $0.003 / task | $0.028 / task lower (GPT-6 Luna leads) |
GPT-5.6 Terra: 2.0% of ChatGPT Pro 5x (2.0% / 1w) per run. GPT-6 Luna: 1.0% of ChatGPT Plus (1.0% / 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 Terra | GPT-6 Luna | Advantage |
|---|---|---|---|
| Capability | 68% | 61% | +8% (GPT-5.6 Terra leads) |
| Median task time | 5m 34s | 1m 8s | 4m 26s faster (GPT-6 Luna leads) |
| Approx. task cost | <$0.057 / task | <$0.011 / task | $0.046 / task lower (GPT-6 Luna leads) |
GPT-5.6 Terra: under 1% of ChatGPT Pro 5x per run. GPT-6 Luna: under 1% of ChatGPT Plus 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 Terra | GPT-6 Luna | Advantage |
|---|---|---|---|
| Capability | 34% | 33% | +1% (GPT-5.6 Terra leads) |
| Median task time | 5m 32s | 1m 37s | 3m 55s faster (GPT-6 Luna leads) |
| Approx. task cost | <$0.230 / task | not measured | - |
GPT-5.6 Terra: under 1% of ChatGPT Pro 5x per good solve. GPT-6 Luna: under 1% of ChatGPT Plus (0.4% / 5h) 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 Terra or GPT-6 Luna?
They are even on our ladder: both clear tier 2 of 5 at 50% capability 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 Terra or GPT-6 Luna?
GPT-5.6 Terra used 2% of ChatGPT Pro 5x's weekly limit per pass, $0.024 per task at the listed price. GPT-6 Luna used 1% of ChatGPT Plus's weekly limit per pass, $0.002 per task at the listed price; at the ~$100 tier the board defaults to that is an estimated ~0.2% of ChatGPT Pro 5x's weekly limit (est, about $0.002 per task). Per task, GPT-6 Luna is about 10x cheaper ($0.002 vs $0.024).
What do GPT-5.6 Terra and GPT-6 Luna cost a month?
GPT-5.6 Terra runs on ChatGPT Pro 5x at $100/month (public price as of 2026-09-05). GPT-6 Luna runs on ChatGPT Plus at $20/month (public price as of 2026-07-20).