Claude Opus 4.8 vs GPT-5.6 Terrafor coding

The verdict

GPT-5.6 Terra wins, 93–89

Same 18 coding tasks, marked blind by three rival labs. GPT-5.6 Terra took 4 tasks, Claude Opus 4.8 took 5, 9 tied. Tested 16 Aug 2026.

Where they differed most

The task — Typed debounce

Write a debounce function in TypeScript that preserves the argument types of the wrapped function, returns a function with a .cancel() method, and does not use 'any'. Explain in one sentence why the naive generic signature loses type information.

Claude Opus 4.85/10

# Debounce Function

```typescript
type Debounced<TArgs extends unknown[]> = {
  (...args: TArgs): void;
  cancel(): void;
};

function debounce<TArgs extends unknown[]>(
  fn: (...args: TArgs) => unknown,
  delay: number
): Debounced<TArgs> {
  let timer: ReturnType<typeof setTimeout> | undefined;

  const debounced = (...args: TArgs): void => {
    if (timer !== undefined) {
      clearTimeout(timer);
    }
    timer = setTimeout(() => {
      timer = undefined;
      fn(...args);
    }, delay);
  };

  debounced.cancel = (): void => {
    if…

GPT-5.6 Terra10/10

```ts
type Debounced<Args extends unknown[]> = {
  (...args: Args): void;
  cancel(): void;
};

export function debounce<Args extends unknown[]>(
  callback: (...args: Args) => unknown,
  delayMs: number,
): Debounced<Args> {
  let timer: ReturnType<typeof setTimeout> | undefined;

  const debounced = (...args: Args): void => {
    if (timer !== undefined) {
      clearTimeout(timer);
    }

    timer = setTimeout(() => {
      timer = undefined;
      void callback(...args);
    }, delayMs);
  };

  debounced.cancel = (): void => {
    if (tim…

Task by task

Task	Claude Opus 4.8	GPT-5.6 Terra
Duration parser	9	8
Find the bug	10	10
SQL without window functions	10	10
Infinite useEffect	10	10
Typed debounce	5	10
Leftmost binary search	10	10
Security review	9	10
Safe migration	8	9
Fix the code not the test	10	9
Race condition	9	9
Retry with backoff	9	8
Recursive type	10	9
Bash one-liner	9	9
Explain and cost	10	10
Regex with limits	9	9
Callback to async	9	9
Diagnose from a trace	9	8
Idempotency	6	10

Full receipts: Claude Opus 4.8, GPT-5.6 Terra · judges gemini-3.1-pro-preview, gpt-5.6-terra, grok-4.5

Questions people ask

Which is better for coding: Claude Opus 4.8 or GPT-5.6 Terra?

GPT-5.6 Terra — it scored 93/100 against 89/100 on our 18-task coding suite, winning 4 tasks to 5 with 9 tied. Every answer was marked blind by three judges from three rival AI labs.

How was this tested?

Both models answered the identical published coding tasks. Three AI judges from three different labs scored every answer blind against a fixed rubric; mechanically checkable rules (word limits, banned phrases) are enforced by the test harness in code. The raw outputs and judge verdicts are downloadable.

More coding head-to-heads: GPT-5.6 Luna vs GPT-5.6 Terra · Claude Opus 4.8 vs GPT-5.6 Luna · GPT-5.6 Sol vs GPT-5.6 Terra · Claude Opus 4.8 vs GPT-5.6 Sol · GLM 5.2 vs GPT-5.6 Terra · GPT-5.3-Codex vs GPT-5.6 Terra

Full ranking: Best AI for coding · model pages: Claude Opus 4.8, GPT-5.6 Terra