Tested prompt · Coding

Merge overlapping intervals: every AI model's reply, tested

We sent this everyday coding prompt to all 16 models in llmwise, the same way the app sends a message, and checked every reply the same way. Here's each one as it came, with whether it passed, what it cost and how long it took.

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Based on 16 of our test runs on September 28, 2026, through OpenRouter with the app's own prompt and settings. Updated September 28, 2026.

Short answer

All 16 models passed this coding prompt's check (tests). The cheapest reply that passed was GPT-6 Luna's, at $0.00011; the fastest, GLM 5.3's in 0.8 s. The dearest reply, Claude Fable 5.1's, cost 194 times as much ($0.0214).

The prompt, as sent, and its check

Checked by tests, the same way for every model.

Merge overlapping intervals (everyday)

Write a JavaScript function mergeIntervals(intervals) that takes an array of [start, end] pairs (numbers, start ≤ end, in any order) and returns a new array in which overlapping or touching intervals are merged, sorted by start.
[1, 3] and [3, 5] touch, so they merge into [1, 5]. Don't change the input array.
Reply with the whole function in one ```javascript code block: plain JavaScript for Node.js 22, no imports, no TypeScript.

The reply's mergeIntervals runs against these 7 tests; it passes when all of them do.

mergeIntervals([[1, 3], [2, 6], [8, 10], [15, 18]])  // → [[1, 6], [8, 10], [15, 18]]
mergeIntervals([[1, 4], [4, 5]])  // → [[1, 5]]
mergeIntervals([])  // → []
mergeIntervals([[5, 7], [1, 2]])  // → [[1, 2], [5, 7]]
mergeIntervals([[1, 10], [2, 3], [4, 5]])  // → [[1, 10]]
mergeIntervals([[1, 2], [2, 2], [2, 3]])  // → [[1, 3]]
(() => { const input = [[3, 4], [1, 2]]; mergeIntervals(input); return input; })()  // → [[3, 4], [1, 2]]

Exactly what this prompt's replies are checked against, with every other prompt of our test runs.

Every model's result

All 16 models on this prompt, in catalog order.

Every model's reply to “Merge overlapping intervals”
Model	Result	Cost	Time	Reply
Claude Fable 5.1Anthropic	Passed: All 7 tests passed.	$0.0214	5.3 s	275 tokens
Claude Opus 5.5Anthropic	Passed: All 7 tests passed.	$0.0077	3.7 s	234 tokens
Claude Sonnet 5.5Anthropic	Passed: All 7 tests passed.	$0.0033	1.4 s	180 tokens
Claude Sonnet 5Anthropic	Passed: All 7 tests passed.	$0.0034	2.7 s	216 tokens
Claude Haiku 4.5Anthropic	Passed: All 7 tests passed.	$0.0017	2.0 s	239 tokens
GPT-6 AstraOpenAI	Passed: All 7 tests passed.	$0.0108	2.6 s	127 tokens
GPT-6 SolOpenAI	Passed: All 7 tests passed.	$0.0022	1.7 s	130 tokens
GPT-6 LunaOpenAI	Passed: All 7 tests passed.	$0.00011	1.5 s	130 tokens
Gemini 3.1 Pro (preview)Google	Passed: All 7 tests passed.	$0.0103	8.6 s	196 tokens
Gemini 3.8 FlashGoogle	Passed: All 7 tests passed.	$0.0012	3.8 s	229 tokens
DeepSeek V4.1 FlashDeepSeek	Passed: All 7 tests passed.	$0.00014	1.5 s	187 tokens
DeepSeek V4 ProDeepSeek	Passed: All 7 tests passed.	$0.00048	6.6 s	174 tokens
Grok 4.7xAI	Passed: All 7 tests passed.	$0.0025	3.8 s	187 tokens
Kimi K3Moonshot	Passed: All 7 tests passed.	$0.0036	2.0 s	148 tokens
GLM 5.3Z.ai	Passed: All 7 tests passed.	$0.00082	0.8 s	113 tokens
GLM 5.3 FlashZ.ai	Passed: All 7 tests passed.	$0.00024	9.6 s	205 tokens

Cost: what OpenRouter charged us for the reply. Time: from sending to the whole reply. Reply: its length in tokens, thinking not counted. In llmwise you pay per message, not per token: each of these replies counted as one message on Pro.

Every reply

Every reply passed: here they are from the cheapest up.

GPT-6 Luna

Passed: All 7 tests passed.

```javascript
function mergeIntervals(intervals) {
  const sorted = intervals
    .map(([start, end]) => [start, end])
    .sort((a, b) => a[0] - b[0]);

  const merged = [];

  for (const [start, end] of sorted) {
    const last = merged[merged.length - 1];

    if (!last || start > last[1]) {
      merged.push([start, end]);
    } else {
      last[1] = Math.max(last[1], end);
    }
  }

  return merged;
}
```

449 tokens in, 130 out · 1.5 s · $0.0001 · 1 message on Pro · answered by openai/gpt-6-luna via OpenAI · September 27, 2026

DeepSeek V4.1 Flash

Passed: All 7 tests passed.

```javascript
function mergeIntervals(intervals) {
  if (intervals.length === 0) return [];

  const sorted = intervals
    .map(([start, end]) => [start, end])
    .sort((a, b) => a[0] - b[0] || a[1] - b[1]);

  const merged = [sorted[0]];

  for (let i = 1; i < sorted.length; i++) {
    const [start, end] = sorted[i];
    const last = merged[merged.length - 1];

    if (start <= last[1]) {
      // overlapping or touching (start === last[1]) -> extend
      if (end > last[1]) last[1] = end;
    } else {
      merged.push([start, end]);
    }
  }

  return merged;
}
```

489 tokens in, 199 out (12 of them reasoning) · 1.5 s · $0.0001 · 1 message on Pro · answered by deepseek/deepseek-v4.1-flash via Wafer · September 27, 2026

GLM 5.3 Flash

Passed: All 7 tests passed.

```javascript
function mergeIntervals(intervals) {
  // Sort a copy by start so the input array is left unchanged
  const sorted = [...intervals].sort((a, b) => a[0] - b[0]);

  const merged = [];
  for (const [start, end] of sorted) {
    const last = merged[merged.length - 1];
    // Merge when overlapping ([1,4] & [2,5]) or touching ([1,3] & [3,5])
    if (last && start <= last[1]) {
      last[1] = Math.max(last[1], end);
    } else {
      merged.push([start, end]);
    }
  }
  return merged;
}
```

Example: `mergeIntervals([[5, 7], [1, 3], [3, 5], [8, 10]])` → `[[1, 7], [8, 10]]`.

463 tokens in, 287 out (82 of them reasoning) · 9.6 s · $0.0002 · 1 message on Pro · answered by z-ai/glm-5.3-flash via Wafer · September 27, 2026

DeepSeek V4 Pro

Passed: All 7 tests passed.

```javascript
function mergeIntervals(intervals) {
  if (intervals.length === 0) return [];

  const sorted = intervals
    .map(([start, end]) => [start, end])
    .sort((a, b) => a[0] - b[0] || a[1] - b[1]);

  const merged = [sorted[0].slice()];

  for (let i = 1; i < sorted.length; i++) {
    const last = merged[merged.length - 1];
    const [start, end] = sorted[i];

    if (start <= last[1]) {
      if (end > last[1]) last[1] = end;
    } else {
      merged.push([start, end]);
    }
  }

  return merged;
}
```

461 tokens in, 457 out (283 of them reasoning) · 6.6 s · $0.0005 · 1 message on Pro · answered by deepseek/deepseek-v4-pro-0813 via StreamLake · September 27, 2026

GLM 5.3

Passed: All 7 tests passed.

```javascript
function mergeIntervals(intervals) {
  const sorted = [...intervals].sort((a, b) => a[0] - b[0]);
  const result = [];
  for (const [start, end] of sorted) {
    const last = result[result.length - 1];
    if (last && start <= last[1]) {
      last[1] = Math.max(last[1], end);
    } else {
      result.push([start, end]);
    }
  }
  return result;
}
```

486 tokens in, 114 out (1 of them reasoning) · 0.8 s · $0.0008 · 1 message on Pro · answered by z-ai/glm-5.3 via Wafer · September 27, 2026

Gemini 3.8 Flash

Passed: All 7 tests passed.

```javascript
function mergeIntervals(intervals) {
  if (!intervals || intervals.length <= 1) {
    return intervals ? intervals.map(interval => [...interval]) : [];
  }

  // Clone and sort by start time, breaking ties by end time
  const sorted = intervals
    .map(interval => [...interval])
    .sort((a, b) => a[0] - b[0] || a[1] - b[1]);

  const merged = [sorted[0]];

  for (let i = 1; i < sorted.length; i++) {
    const current = sorted[i];
    const lastMerged = merged[merged.length - 1];

    // Overlapping or touching intervals
    if (current[0] <= lastMerged[1]) {
      lastMerged[1] = Math.max(lastMerged[1], current[1]);
    } else {
      merged.push(current);
    }
  }

  return merged;
}
```

477 tokens in, 229 out · 3.8 s · $0.0012 · 1 message on Pro · answered by google/gemini-3.8-flash via Google · September 27, 2026

Claude Haiku 4.5

Passed: All 7 tests passed.

```javascript
function mergeIntervals(intervals) {
  if (intervals.length === 0) return [];

  // Sort intervals by start time, then by end time
  const sorted = intervals.map(interval => [...interval]).sort((a, b) => {
    return a[0] - b[0] || a[1] - b[1];
  });

  const merged = [sorted[0]];

  for (let i = 1; i < sorted.length; i++) {
    const current = sorted[i];
    const last = merged[merged.length - 1];

    // If current interval overlaps or touches the last merged interval
    if (current[0] <= last[1]) {
      // Merge by extending the end of the last interval
      last[1] = Math.max(last[1], current[1]);
    } else {
      // No overlap, add as new interval
      merged.push(current);
    }
  }

  return merged;
}
```

481 tokens in, 239 out · 2.0 s · $0.0017 · 1 message on Pro · answered by anthropic/claude-haiku-4.5 via Amazon Bedrock · September 27, 2026

GPT-6 Sol

Passed: All 7 tests passed.

```javascript
function mergeIntervals(intervals) {
  const sorted = intervals
    .map(([start, end]) => [start, end])
    .sort((a, b) => a[0] - b[0]);

  const merged = [];

  for (const [start, end] of sorted) {
    const last = merged[merged.length - 1];

    if (last && start <= last[1]) {
      last[1] = Math.max(last[1], end);
    } else {
      merged.push([start, end]);
    }
  }

  return merged;
}
```

449 tokens in, 130 out · 1.7 s · $0.0022 · 1 message on Pro · answered by openai/gpt-6-sol via OpenAI · September 27, 2026

Grok 4.7

Passed: All 7 tests passed.

```javascript
function mergeIntervals(intervals) {
  if (!intervals || intervals.length === 0) return [];

  const sorted = intervals
    .map(([start, end]) => [start, end])
    .sort((a, b) => a[0] - b[0] || a[1] - b[1]);

  const merged = [[sorted[0][0], sorted[0][1]]];

  for (let i = 1; i < sorted.length; i++) {
    const [start, end] = sorted[i];
    const last = merged[merged.length - 1];
    if (start <= last[1]) {
      if (end > last[1]) last[1] = end;
    } else {
      merged.push([start, end]);
    }
  }

  return merged;
}
```

1,683 tokens in, 306 out (119 of them reasoning) · 3.8 s · $0.0025 · 1 message on Pro · answered by x-ai/grok-4.7 via xAI · September 27, 2026

Claude Sonnet 5.5

Passed: All 7 tests passed.

```javascript
function mergeIntervals(intervals) {
  const sorted = intervals
    .map(([start, end]) => [start, end])
    .sort((a, b) => a[0] - b[0] || a[1] - b[1]);

  const result = [];
  for (const [start, end] of sorted) {
    const last = result[result.length - 1];
    if (last && start <= last[1]) {
      if (end > last[1]) last[1] = end;
    } else {
      result.push([start, end]);
    }
  }
  return result;
}
```

623 tokens in, 180 out · 1.4 s · $0.0033 · 1 message on Pro · answered by anthropic/claude-sonnet-5.5 via Anthropic · September 28, 2026

Claude Sonnet 5

Passed: All 7 tests passed.

```javascript
function mergeIntervals(intervals) {
  if (!intervals || intervals.length === 0) return [];

  const sorted = intervals
    .map(([a, b]) => [a, b])
    .sort((x, y) => x[0] - y[0]);

  const result = [sorted[0]];

  for (let i = 1; i < sorted.length; i++) {
    const [start, end] = sorted[i];
    const last = result[result.length - 1];

    if (start <= last[1]) {
      last[1] = Math.max(last[1], end);
    } else {
      result.push([start, end]);
    }
  }

  return result;
}
```

619 tokens in, 216 out · 2.7 s · $0.0034 · 1 message on Pro · answered by anthropic/claude-sonnet-5 via Claude Platform on AWS · September 27, 2026

Kimi K3

Passed: All 7 tests passed.

```javascript
function mergeIntervals(intervals) {
  const sorted = intervals
    .map(([start, end]) => [start, end])
    .sort((a, b) => a[0] - b[0] || a[1] - b[1]);

  const merged = [];
  for (const [start, end] of sorted) {
    const last = merged[merged.length - 1];
    if (last && start <= last[1]) {
      last[1] = Math.max(last[1], end);
    } else {
      merged.push([start, end]);
    }
  }
  return merged;
}
```

536 tokens in, 152 out (4 of them reasoning) · 2.0 s · $0.0036 · 1 message on Pro · answered by moonshotai/kimi-k3 via Together · September 27, 2026

Claude Opus 5.5

Passed: All 7 tests passed.

```javascript
function mergeIntervals(intervals) {
  if (!Array.isArray(intervals) || intervals.length === 0) return [];

  const sorted = intervals
    .map(([start, end]) => [start, end])
    .sort((a, b) => a[0] - b[0] || a[1] - b[1]);

  const result = [sorted[0]];

  for (let i = 1; i < sorted.length; i++) {
    const last = result[result.length - 1];
    const [start, end] = sorted[i];

    if (start <= last[1]) {
      if (end > last[1]) last[1] = end;
    } else {
      result.push([start, end]);
    }
  }

  return result;
}
```

621 tokens in, 234 out · 3.7 s · $0.0077 · 1 message on Pro · answered by anthropic/claude-opus-5.5 via Claude Platform on AWS · September 27, 2026

Gemini 3.1 Pro

Passed: All 7 tests passed.

```javascript
function mergeIntervals(intervals) {
  if (!intervals || intervals.length === 0) {
    return [];
  }

  const sorted = [...intervals].sort((a, b) => a[0] - b[0]);
  const result = [];
  
  let current = [sorted[0][0], sorted[0][1]];

  for (let i = 1; i < sorted.length; i++) {
    const next = sorted[i];
    
    if (next[0] <= current[1]) {
      current[1] = Math.max(current[1], next[1]);
    } else {
      result.push(current);
      current = [next[0], next[1]];
    }
  }
  
  result.push(current);
  return result;
}
```

477 tokens in, 780 out (584 of them reasoning) · 8.6 s · $0.0103 · 1 message on Pro · answered by google/gemini-3.1-pro-preview via Google · September 27, 2026

GPT-6 Astra

Passed: All 7 tests passed.

```javascript
function mergeIntervals(intervals) {
  const sorted = intervals.map(([start, end]) => [start, end]);
  sorted.sort((a, b) => a[0] - b[0]);

  const merged = [];

  for (const [start, end] of sorted) {
    const last = merged[merged.length - 1];

    if (last && start <= last[1]) {
      last[1] = Math.max(last[1], end);
    } else {
      merged.push([start, end]);
    }
  }

  return merged;
}
```

449 tokens in, 127 out · 2.6 s · $0.0108 · 1 message on Pro · answered by openai/gpt-6-astra via OpenAI · September 27, 2026

Claude Fable 5.1

Passed: All 7 tests passed.

```javascript
function mergeIntervals(intervals) {
  if (!Array.isArray(intervals) || intervals.length === 0) return [];

  // Copy so the input (and its inner pairs) is never mutated
  const sorted = intervals
    .map(([start, end]) => [start, end])
    .sort((a, b) => a[0] - b[0] || a[1] - b[1]);

  const result = [sorted[0]];

  for (let i = 1; i < sorted.length; i++) {
    const [start, end] = sorted[i];
    const last = result[result.length - 1];

    if (start <= last[1]) {
      // Overlapping or touching: extend the current interval
      if (end > last[1]) last[1] = end;
    } else {
      result.push([start, end]);
    }
  }

  return result;
}
```

621 tokens in, 275 out · 5.3 s · $0.0214 · 1 message on Pro · answered by anthropic/claude-fable-5.1 via Anthropic · September 27, 2026

More coding prompts

The other coding prompts, each with every model's reply, and the results across all five.

Questions

Which AI does best on “Merge overlapping intervals”?

What does a reply to “Merge overlapping intervals” cost?

Through the models' APIs, what OpenRouter charged us ran from $0.00011 (GPT-6 Luna) to $0.0214 (Claude Fable 5.1) for this prompt. In llmwise you don't pay by the token: a reply like these counts as one message on Pro, whichever model answers.

Claude, GPT, Gemini, DeepSeek, Grok, Kimi, and GLM, in one chat.

See what a message costs before you send it. Free is 5 messages to try; sign in with an email link, no password or card.

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