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A · closed · GPT-5.x

GPT-5.5

OpenAI

B · closed · GPT-5.x

GPT-5.6 Terra

OpenAI

7:8

overall capability wins (2 ties across 17 scored). GPT-5.6 Terra leads overall.

  • Reasoning5:2
  • Coding1:4
  • Arena1:0
  • Agents0:1
  • Tool use0:1
  • Composite indices0:2
  • Pricing0:3
  • Speed0:2

Verdict

GPT-5.6 Terra leads coding (widest gap: +11.1 on WebDev Elo); GPT-5.5 edges reasoning & knowledge; GPT-5.5 ranks higher on LMArena (+10 Elo).

  • GPT-5.6 Terra leads coding (widest gap: +11.1 on WebDev Elo)
  • GPT-5.5 edges reasoning & knowledge
  • GPT-5.5 ranks higher on LMArena (+10 Elo)
  • GPT-5.6 Terra is ~2.5x cheaper on a blended token basis than GPT-5.5

Cost for 1M in + 250K out

Illustrative chat workload at primary-provider list prices.

GPT-5.5
$12.50
GPT-5.6 Terra
$5

GPT-5.6 Terra is about 2.5x cheaper on this workload.

Price per 1M tokens

Full comparison

Organization

OpenAI

OpenAI

Family

GPT-5.x

GPT-5.x

License

Proprietary

Proprietary

Open weights

No

No

Release

Apr 23, 2026

Jul 9, 2026

Knowledge cutoff

-

-

API / provider

OpenAI

OpenAI

Modalities

text, image → text

text, image → text

Specs

Context window

1.1M

1.1M

tie

Max output

128K

128K

tie

Parameters

—

—

—

Pricing

Input $/1M

$5

$2

B +$3

Output $/1M

$30

$12

B +$18

Blended $/1M (3∶1)

$11.25

$4.50

B +$6.75

Speed

tok/s

70

135

B +65

TTFT (s)

0.5

0.3

B +0.20

Reasoning

MMLU-Pro

—

—

—

GPQA Diamond

93.5

92.5

A +1.0 pts

Humanity's Last Exam

45.8

42.9

A +2.9 pts

AIME 2025

—

—

—

MATH-500

—

—

—

Humanity's Last Exam (with tools)

—

—

—

AA-Omniscience Accuracy

58.0

46.8

A +11.2 pts

AA-LCR v1.1

84.3

83.0

A +1.3 pts

CritPt

27.1

30.0

B +2.9 pts

MMMU-Pro

79.9

80.7

B +0.8 pts

IFBench

75.9

71.2

A +4.7 pts

Chartography

—

—

—

Chartography (With Tools)

—

—

—

Coding

SWE-bench Verified

—

—

—

SWE-bench Pro

58.6

63.4

B +4.8 pts

SWE-bench Multilingual

—

—

—

LiveCodeBench

—

—

—

Terminal-Bench 2.1

84.3

88.0

B +3.7 pts

Aider Polyglot

—

—

—

Terminal-Bench 3

—

20.8

—

BigCodeBench

—

—

—

SciCode

55.8

55.0

A +0.8 pts

CursorBench

58.4

64.9

B +6.5 pts

SWE-Rebench

62.7

—

—

NL2Repo-Bench

—

—

—

DeepSWE

67.0

—

—

WebDev Arena

1,510

1,521

B +11 Elo

Terminal-Bench 4.0

—

21.5

—

CursorBench 4.0

—

—

—

FrontierCode v1.1 (Main)

—

—

—

Arena

LMArena Elo

1,476

1,466

A +10 Elo

GPT-5.5

Context
1.1M / 128K out
Parameters
—
Price
$5 / $30
Speed
70 tok/s · 0.5s TTFT
Modalities
text, image → text
License
Proprietary

Prior OpenAI flagship with strong coding and long context; still widely used alongside the newer 5.6 family.

GPT-5.6 Terra

Context
1.1M / 128K out
Parameters
—
Price
$2 / $12
Speed
135 tok/s · 0.3s TTFT
Modalities
text, image → text
License
Proprietary

Balanced GPT-5.6 mid-tier for everyday work; July 30, 2026 API cut brought Standard rates to $2/$12 (20% lower), with strong throughput for the price.

Benchmark charts

Winner bars are emphasized. Per-benchmark deltas sit above each chart.

Reasoning & knowledge

GPQA: A +1.0HLE: A +2.9CritPt: B +2.9AA-LCR: A +1.3Omniscience Acc.: A +11.2MMMU-Pro: B +0.8IFBench: A +4.7

Coding

SWE-Pro: B +4.8TermBench: B +3.7SciCode: A +0.8CursorBench: B +6.5WebDev Elo: B +11

Tool use & function calling

τ³-Banking: B +1.2

Agents & computer use

GDPval-AA: B +84

Arena

Arena Elo: A +10

Composite indices

AA Index: B +8.2AA Index v4.3: B +3.7

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