Claude Fable 5 vs GPT-5.6 Terra
Claude Fable 5 was superseded by Claude Fable 5.1. The grades below are the last ones measured, so read them as history rather than as this week's board. See the current roster.
Claude Fable 5 leads overall, C to D. GPT-5.6 Terra is about 8.7x cheaper per task. By suite, Claude Fable 5 takes real-world issues (C- to D+) and spec planning (C to D+). Take GPT-5.6 Terra 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-5.6 Terra vs Claude Fable 5
Claude Fable 5 leads overall, C to D. By suite: Claude Fable 5 takes real-world issues, C- to D+ (60% vs 50% capability); Claude Fable 5 takes spec planning, C to D+ (63% vs 53% capability); Claude Fable 5 takes vibe coding, C+ to F (74% vs 34% capability). Claude Fable 5 used 7% of Claude Max 20x's weekly limit per pass, $0.169 per task at the listed price; at the ~$100 tier the board defaults to that is an estimated ~14% of Claude Max 5x's weekly limit (est, about $0.169 per task). 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 Terra is about 8.7x cheaper ($0.019 vs $0.169). GPT-5.6 Terra is faster on real-world issues: a median task takes 2m 18s against 2m 37s. Both finished every task on it. Reasons to pick GPT-5.6 Terra anyway: it is cheaper per task ($0.019 vs $0.169) and it is faster on real-world issues (2m 18s vs 2m 37s median).
Changed since the previous graded week: Claude Fable 5: real-world issues C+ to C-, vibe coding C to C+; 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 Fable 5 | GPT-5.6 Terra | Advantage |
|---|---|---|---|
| Capability | 60% | 50% | +10% (Claude Fable 5 leads) |
| Median task time | 2m 37s | 2m 18s | 19s faster (GPT-5.6 Terra leads) |
| Approx. task cost | $0.153 / task | $0.021 / task | $0.132 / task lower (GPT-5.6 Terra leads) |
Claude Fable 5: 33.0% of Claude Max 20x (33.0% / 5h, 5.0% / 1w) per run. Its weekly limit holds about 7 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 Fable 5 | GPT-5.6 Terra | Advantage |
|---|---|---|---|
| Capability | 63% | 53% | +10% (Claude Fable 5 leads) |
| Median task time | 5m 32s | 2m 37s | 2m 55s faster (GPT-5.6 Terra leads) |
| Approx. task cost | $0.230 / task | $0.011 / task | $0.218 / task lower (GPT-5.6 Terra leads) |
Claude Fable 5: 10.0% of Claude Max 20x (10.0% / 5h, 2.0% / 1w) per run. Its weekly limit holds about 7 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 Fable 5 | GPT-5.6 Terra | Advantage |
|---|---|---|---|
| Capability | 74% | 34% | +40% (Claude Fable 5 leads) |
| Median task time | 5m 28s | 2m 47s | 2m 41s faster (GPT-5.6 Terra leads) |
| Approx. task cost | $0.184 / task | $0.028 / task | $0.156 / task lower (GPT-5.6 Terra leads) |
Claude Fable 5: 2.8% of Claude Max 20x (2.8% / 5h, 0.4% / 1w) per good solve. Its weekly limit holds about 7 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 Fable 5 or GPT-5.6 Terra?
Claude Fable 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 2026-08-30.
Which is cheaper per task, Claude Fable 5 or GPT-5.6 Terra?
Claude Fable 5 used 7% of Claude Max 20x's weekly limit per pass, $0.169 per task at the listed price; at the ~$100 tier the board defaults to that is an estimated ~14% of Claude Max 5x's weekly limit (est, about $0.169 per task). 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 Terra is about 8.7x cheaper ($0.019 vs $0.169).
What do Claude Fable 5 and GPT-5.6 Terra cost a month?
Claude Fable 5 runs on Claude Max 20x at $200/month (public price as of 2026-08-05). GPT-5.6 Terra runs on ChatGPT Plus at $20/month (public price as of 2026-07-20).