Claude Sonnet 5.5 vs GPT-5.6 Terra
Claude Sonnet 5.5 leads overall, C- to D. Claude Sonnet 5.5 is about 6.7x cheaper per task. By suite, Claude Sonnet 5.5 takes real-world issues (C- to D+) and spec planning (C+ to D+). The data gives no reason to pick GPT-5.6 Terra over Claude Sonnet 5.5 this week.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 Claude Sonnet 5.5
Claude Sonnet 5.5 leads overall, C- to D. By suite: Claude Sonnet 5.5 takes real-world issues, C- to D+ (60% vs 50% capability); Claude Sonnet 5.5 takes spec planning, C+ to D+ (74% vs 53% capability); Claude Sonnet 5.5 takes vibe coding, D+ to F (48% vs 34% capability). Claude Sonnet 5.5 used <1% of Claude Max 5x's weekly limit per pass, $0.003 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, Claude Sonnet 5.5 is about 6.7x cheaper ($0.003 vs $0.019). Claude Sonnet 5.5 is faster on real-world issues: a median task takes 37s against 2m 18s. Both finished every task on it. The data gives no reason to pick GPT-5.6 Terra over Claude Sonnet 5.5 this week.
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.
| Dimension | Claude Sonnet 5.5 | GPT-5.6 Terra | Advantage |
|---|---|---|---|
| Capability | 60% | 50% | +10% (Claude Sonnet 5.5 leads) |
| Median task time | 37s | 2m 18s | 1m 41s faster (Claude Sonnet 5.5 leads) |
| Approx. task cost | $0.002 / task | $0.021 / task | $0.020 / task lower (Claude Sonnet 5.5 leads) |
Claude Sonnet 5.5: 4.0% of Claude Max 5x (4.0% / 5h) per run. Its weekly limit holds about 13.8 of the week's 33.6 5h windows. 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 | Claude Sonnet 5.5 | GPT-5.6 Terra | Advantage |
|---|---|---|---|
| Capability | 74% | 53% | +21% (Claude Sonnet 5.5 leads) |
| Median task time | 3m 25s | 2m 37s | 47s faster (GPT-5.6 Terra leads) |
| Approx. task cost | $0.007 / task | $0.011 / task | $0.005 / task lower (Claude Sonnet 5.5 leads) |
Claude Sonnet 5.5: 4.0% of Claude Max 5x (4.0% / 5h) per run. Its weekly limit holds about 13.8 of the week's 33.6 5h windows. 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 | Claude Sonnet 5.5 | GPT-5.6 Terra | Advantage |
|---|---|---|---|
| Capability | 48% | 34% | +14% (Claude Sonnet 5.5 leads) |
| Median task time | 56s | 2m 47s | 1m 51s faster (Claude Sonnet 5.5 leads) |
| Approx. task cost | $0.001 / task | $0.028 / task | $0.026 / task lower (Claude Sonnet 5.5 leads) |
Claude Sonnet 5.5: 0.2% of Claude Max 5x (0.2% / 5h) per good solve. Its weekly limit holds about 13.8 of the week's 33.6 5h windows. 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, Claude Sonnet 5.5 or GPT-5.6 Terra?
Claude Sonnet 5.5 clears higher: tier 4 of 5 versus tier 2 for GPT-5.6 Terra on real-world@v3, our private suite of real-world coding problems. Latest measurement 2026-09-28.
Which is cheaper per task, Claude Sonnet 5.5 or GPT-5.6 Terra?
Claude Sonnet 5.5 used <1% of Claude Max 5x's weekly limit per pass, $0.003 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, Claude Sonnet 5.5 is about 6.7x cheaper ($0.003 vs $0.019).
What do Claude Sonnet 5.5 and GPT-5.6 Terra cost a month?
Claude Sonnet 5.5 runs on Claude Max 5x at $100/month (public price as of 2026-07-20). GPT-5.6 Terra runs on ChatGPT Plus at $20/month (public price as of 2026-07-20).