GPT-5.6 Terra vs GPT-6 Astra
GPT-6 Astra leads overall, C to D. GPT-5.6 Terra is about 2.7x cheaper per task. By suite, GPT-5.6 Terra takes real-world issues (D+ to D) and GPT-6 Astra takes spec planning (C+ to D+). Take GPT-5.6 Terra anyway when you want the side that is cheaper per task and ahead 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 Astra vs GPT-5.6 Terra
GPT-6 Astra leads overall, C to D. By suite: GPT-5.6 Terra takes real-world issues, D+ to D (50% vs 43% capability); GPT-6 Astra takes spec planning, C+ to D+ (74% vs 53% capability); GPT-6 Astra takes vibe coding, C+ to F (74% vs 34% capability). 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). GPT-6 Astra used 22% of ChatGPT Plus's weekly limit per pass, $0.053 per task at the listed price; at the ~$100 tier the board defaults to that is an estimated ~4.4% of ChatGPT Pro 5x's weekly limit (est, about $0.053 per task). Per task, GPT-5.6 Terra is about 2.7x cheaper ($0.019 vs $0.053). GPT-6 Astra is faster on real-world issues: a median task takes 2m 13s against 2m 18s. Both finished every task on it. Reasons to pick GPT-5.6 Terra anyway: it is cheaper per task ($0.019 vs $0.053) and it leads on real-world issues (D+ to D).
Changed since W36: 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; GPT-6 Astra has one graded week under this version (W40).
| Dimension | GPT-5.6 Terra | GPT-6 Astra | Advantage |
|---|---|---|---|
| Capability | 50% | 43% | +7% (GPT-5.6 Terra leads) |
| Median task time | 2m 18s | 2m 13s | 4s faster (GPT-6 Astra leads) |
| Approx. task cost | $0.021 / task | $0.052 / task | $0.031 / task lower (GPT-5.6 Terra leads) |
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. GPT-6 Astra: 17.0% of ChatGPT Plus (112.0% / 5h, 17.0% / 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 Astra | Advantage |
|---|---|---|---|
| Capability | 53% | 74% | +21% (GPT-6 Astra leads) |
| Median task time | 2m 37s | 3m 5s | 28s faster (GPT-5.6 Terra leads) |
| Approx. task cost | $0.011 / task | $0.057 / task | $0.046 / task lower (GPT-5.6 Terra leads) |
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. GPT-6 Astra: 5.0% of ChatGPT Plus (27.0% / 5h, 5.0% / 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 Astra | Advantage |
|---|---|---|---|
| Capability | 34% | 74% | +40% (GPT-6 Astra leads) |
| Median task time | 2m 47s | 2m 40s | 7s faster (GPT-6 Astra leads) |
| Approx. task cost | $0.028 / task | $0.046 / task | $0.018 / task lower (GPT-5.6 Terra leads) |
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. GPT-6 Astra: 1.0% of ChatGPT Plus (7.2% / 5h, 1.0% / 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 Terra or GPT-6 Astra?
Both clear tier 2 of 5, but GPT-5.6 Terra scores higher on capability: 50% versus 43% on real-world@v3, our private suite of real-world coding problems. Latest measurement 2026-09-28.
Which is cheaper per task, GPT-5.6 Terra or GPT-6 Astra?
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). GPT-6 Astra used 22% of ChatGPT Plus's weekly limit per pass, $0.053 per task at the listed price; at the ~$100 tier the board defaults to that is an estimated ~4.4% of ChatGPT Pro 5x's weekly limit (est, about $0.053 per task). Per task, GPT-5.6 Terra is about 2.7x cheaper ($0.019 vs $0.053).
What do GPT-5.6 Terra and GPT-6 Astra cost a month?
GPT-5.6 Terra runs on ChatGPT Plus at $20/month (public price as of 2026-07-20). GPT-6 Astra runs on ChatGPT Plus at $20/month (public price as of 2026-07-20).