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Model compare

GPT-5.1 vs GPT-5.5

The readout for GPT-5.1 and GPT-5.5, before the detailed comparison sheet.

Model A

GPT-5.1

OpenAI

Contender
vs

Model B

GPT-5.5

OpenAI

Leading

Key Takeaways

Weighted outcome: GPT-5.5. Benchmark capability categories carry 80%, while price, API performance, and availability carry 20%.

Decision read

GPT-5.5

GPT-5.5 has the higher weighted result; Model A / B score 8 to 92.

Evidence depth

129 data points

Includes 32 benchmark rows, 0 audit samples, and 10 provider examples.

Selection signal

Start with GPT-5.5

The charts below split 42 high-signal samples across speed, scores, and audit health.

Change comparison

Switch either side of this report to compare another model with the same LMSpeed data pipeline.

Select a different model to open a new comparison URL.

Comparison sheet

This report only uses LMSpeed data for GPT-5.1 and GPT-5.5: pricing, speed aggregates, third-party benchmark scores, and shared provider samples.

Model compare
GPT-5.1
GPT-5.5
Overall leaderContenderLeading
Weighted overall score8.0 pts92.0 pts
Benchmark category leads0 categories7 categories
Operational advantagesAverage speed, First-token latencyCheapest input price, Free providers, Provider coverage
Context window400K tokens1.1M tokens
Max output128K tokens128K tokens
Modalities

Input

ImageTextFile

Output

Text

Input

FileImageText

Output

Text
Features
Text inputImage inputFile inputText outputTool callingStructured outputsJSON modeReasoning
Text inputImage inputFile inputText outputTool callingStructured outputsJSON modeReasoning

The overall result weights benchmark capability categories at 80% and price, API speed/latency, and availability at 20%. Recent test volume does not affect the winner, and missing benchmark categories are excluded.

Model metadata

Model compare
GPT-5.1
GPT-5.5
DeveloperOpenAIOpenAI
ReleasedNov 2025Apr 2026
ParametersNo dataNo data
TokenizerGPTGPT
Knowledge cutoffNo data2025-12-01
OpenRouter IDopenai/gpt-5.1openai/gpt-5.5
ReferencesNo dataNo data

When to choose each model

This report only uses LMSpeed data for GPT-5.1 and GPT-5.5: pricing, speed aggregates, third-party benchmark scores, and shared provider samples.

GPT-5.1

GPT-5.1 has these operational advantages: Average speed, First-token latency.

GPT-5.5

GPT-5.5 is stronger in benchmark categories (Agents, Coding, Reasoning, Knowledge, Math) and operational dimensions (Cheapest input price, Free providers, Provider coverage).

Benchmark score comparison

Third-party benchmark profile synced into LMSpeed; only metrics available for both models are shown.

Category performance

Compare benchmark category scores on a 0-100 scale. Select a category to inspect the gap.

Model A coverage
7 / 8
Model B coverage
7 / 8
Shared
7 shared categories

Avg. score

GPT-5.1

51.6

Avg. score

GPT-5.5

57.7

Agents

GPT-5.5 leads by 13.6

GPT-5.147.3
GPT-5.560.9

Coding

GPT-5.5 leads by 9.7

GPT-5.149.6
GPT-5.559.3

Reasoning

GPT-5.5 leads by 5.0

GPT-5.153.8
GPT-5.558.8

Knowledge

GPT-5.5 leads by 3.9

GPT-5.154.4
GPT-5.558.3

Math

GPT-5.5 leads by 2.8

GPT-5.153.4
GPT-5.556.2

Multilingual

No data

GPT-5.1-
GPT-5.5-

Multimodal

GPT-5.5 leads by 6.9

GPT-5.148.8
GPT-5.555.7

Instruction following

GPT-5.5 leads by 1.2

GPT-5.153.6
GPT-5.554.8

Professional benchmark details

Metric-level scores with benchmark source, rank depth, confidence, error, and evaluation date where available.

Aggregatereported

BenchLM overall score

SourceGPT-5.1

GPT-5.1

66.0

Rank #32/112 · confidence 2 · eval date 2025-11-13

+3.0

GPT-5.5

winner

69.0

Rank #20/112 · confidence 4 · eval date 2026-04-23

Pricingverified

Input price

SourceGPT-5.1 (high)

GPT-5.1

winner

$1.25/M

Rank #123/186 · confidence 4

+$3.75/M

GPT-5.5

$5.00/M

Rank #168/186 · confidence 4

Pricingverified

Blended price

SourceGPT-5.1 (high)

GPT-5.1

winner

$3.44/M

Rank #139/186 · confidence 4

+$7.81/M

GPT-5.5

$11.25/M

Rank #174/186 · confidence 4

Pricingverified

Output price

SourceGPT-5.1 (high)

GPT-5.1

winner

$10.00/M

Rank #142/186 · confidence 4

+$20.00/M

GPT-5.5

$30.00/M

Rank #174/186 · confidence 4

Reasoningreported

AA-LCR

SourceGPT-5.1

GPT-5.1

80.0

Rank #24/106 · confidence 2 · eval date 2025-11-13

+4.3

GPT-5.5

winner

84.3

Rank #3/106 · confidence 4 · eval date 2026-04-23

Reasoningverified

GPQA

SourceGPT-5.1 (high)

GPT-5.1

87.3%

Rank #52/218 · confidence 4

+6.2%

GPT-5.5

winner

93.5%

Rank #8/218 · confidence 4

Reasoningreported

CritPt

SourceGPT-5.1

GPT-5.1

4.9

Rank #48/88 · confidence 2 · eval date 2025-11-13

+22.2

GPT-5.5

winner

27.1

Rank #9/88 · confidence 4 · eval date 2026-04-23

Reasoningverified

HLE

SourceGPT-5.1 (high)

GPT-5.1

28.5%

Rank #61/216 · confidence 4

+17.3%

GPT-5.5

winner

45.8%

Rank #16/216 · confidence 4

Reasoningreported

BenchLM Reasoning score

SourceGPT-5.1

GPT-5.1

winner

76.0

Rank #17/67 · confidence 2 · eval date 2025-11-13

+12.0

GPT-5.5

64.0

Rank #43/67 · confidence 4 · eval date 2026-04-23

Codingreported

Vibe Code Bench

SourceGPT-5.1

GPT-5.1

24.6

Rank #18/33 · confidence 2 · eval date 2025-11-13

+45.2

GPT-5.5

winner

69.8

Rank #2/33 · confidence 4 · eval date 2026-04-23

Codingreported

AA Coding Index

SourceGPT-5.1

GPT-5.1

49.4

Rank #47/75 · confidence 2 · eval date 2025-11-13

+25.5

GPT-5.5

winner

74.9

Rank #12/75 · confidence 4 · eval date 2026-04-23

Codingreported

AA-SciCode

SourceGPT-5.1

GPT-5.1

43.3

Rank #60/113 · confidence 3 · eval date 2025-11-13

+12.5

GPT-5.5

winner

55.8

Rank #16/113 · confidence 4 · eval date 2026-04-23

Mathreported

FrontierMath v2 (Tiers 1-3)

SourceGPT-5.1

GPT-5.1

31.0

Rank #19/47 · confidence 2 · eval date 2025-11-13

+20.7

GPT-5.5

winner

51.7

Rank #4/47 · confidence 4 · eval date 2026-04-23

Mathreported

FrontierMath v2 (Tier 4)

SourceGPT-5.1

GPT-5.1

12.5

Rank #17/36 · confidence 2 · eval date 2025-11-13

+22.9

GPT-5.5

winner

35.4

Rank #7/36 · confidence 4 · eval date 2026-04-23

Mathreported

BenchLM Math score

SourceGPT-5.1

GPT-5.1

49.2

Rank #37/63 · confidence 2 · eval date 2025-11-13

+20.4

GPT-5.5

winner

69.6

Rank #21/63 · confidence 4 · eval date 2026-04-23

Knowledgereported

AA-Omniscience Accuracy

SourceGPT-5.1

GPT-5.1

37.7

Rank #43/106 · confidence 2 · eval date 2025-11-13

+20.3

GPT-5.5

winner

58.0

Rank #6/106 · confidence 4 · eval date 2026-04-23

Knowledgereported

AA-GPQA Diamond

SourceGPT-5.1

GPT-5.1

87.3

Rank #48/113 · confidence 2 · eval date 2025-11-13

+6.2

GPT-5.5

winner

93.5

Rank #8/113 · confidence 4 · eval date 2026-04-23

Knowledgereported

AA-HLE

SourceGPT-5.1

GPT-5.1

28.5

Rank #52/114 · confidence 2 · eval date 2025-11-13

+17.3

GPT-5.5

winner

45.8

Rank #13/114 · confidence 4 · eval date 2026-04-23

Knowledgereported

AA-Omniscience Index

SourceGPT-5.1

GPT-5.1

5.4

Rank #29/45 · confidence 2 · eval date 2025-11-13

+15.1

GPT-5.5

winner

20.5

Rank #18/45 · confidence 4 · eval date 2026-04-23

Knowledgereported

AA-Omniscience Hallucination Rate

SourceGPT-5.1

GPT-5.1

51.9

Rank #74/106 · confidence 2 · eval date 2025-11-13

+37.1

GPT-5.5

winner

89.0

Rank #22/106 · confidence 4 · eval date 2026-04-23

Knowledgereported

BenchLM Knowledge score

SourceGPT-5.1

GPT-5.1

63.6

Rank #55/83 · confidence 2 · eval date 2025-11-13

+15.2

GPT-5.5

winner

78.8

Rank #22/83 · confidence 4 · eval date 2026-04-23

Knowledgereported

Artificial Analysis Intelligence Index

SourceGPT-5.1

GPT-5.1

24.7

Rank #67/117 · confidence 2 · eval date 2025-11-13

+13.9

GPT-5.5

winner

38.6

Rank #31/117 · confidence 4 · eval date 2026-04-23

Multimodalreported

AA-MMMU-Pro

SourceGPT-5.1

GPT-5.1

75.5

Rank #30/68 · confidence 2 · eval date 2025-11-13

+4.4

GPT-5.5

winner

79.9

Rank #15/68 · confidence 4 · eval date 2026-04-23

Multimodalreported

BenchLM Multimodal Grounded score

SourceGPT-5.1

GPT-5.1

71.2

Rank #25/56 · confidence 2 · eval date 2025-11-13

+0.1

GPT-5.5

winner

71.3

Rank #24/56 · confidence 4 · eval date 2026-04-23

Multimodalreported

Design Arena Website

SourceGPT-5.1

GPT-5.1

1199.0

Rank #51/78 · confidence 2 · eval date 2025-11-13

+70.0

GPT-5.5

winner

1269.0

Rank #30/78 · confidence 4 · eval date 2026-04-23

Instruction followingreported

BenchLM Instruction Following score

SourceGPT-5.1

GPT-5.1

89.3

Rank #20/52 · confidence 2 · eval date 2025-11-13

+3.9

GPT-5.5

winner

93.2

Rank #5/52 · confidence 4 · eval date 2026-04-23

Instruction followingreported

AA-IFBench

SourceGPT-5.1

GPT-5.1

72.9

Rank #26/84 · confidence 2 · eval date 2025-11-13

+3.0

GPT-5.5

winner

75.9

Rank #13/84 · confidence 4 · eval date 2026-04-23

Agentsreported

Gert Labs

SourceGPT-5.1

GPT-5.1

41.2

Rank #34/49 · confidence 2 · eval date 2025-11-13

+31.7

GPT-5.5

winner

72.9

Rank #2/49 · confidence 4 · eval date 2026-04-23

Agentsreported

τ²-bench results

SourceGPT-5.1

GPT-5.1

81.9

Rank #53/82 · confidence 2 · eval date 2025-11-13

+16.1

GPT-5.5

winner

98.0

Rank #8/82 · confidence 4 · eval date 2026-04-23

Agentsreported

GDPval-AA

SourceGPT-5.1

GPT-5.1

21.5

Rank #52/66 · confidence 2 · eval date 2025-11-13

+23.3

GPT-5.5

winner

44.8

Rank #22/66 · confidence 4 · eval date 2026-04-23

Agentsreported

GDPval-AA

SourceGPT-5.1

GPT-5.1

930.0

Rank #53/72 · confidence 2 · eval date 2025-11-13

+466.0

GPT-5.5

winner

1396.0

Rank #22/72 · confidence 4 · eval date 2026-04-23

Agentsreported

AA Agentic Index

SourceGPT-5.1

GPT-5.1

21.6

Rank #45/70 · confidence 3 · eval date 2025-11-13

+15.7

GPT-5.5

winner

37.3

Rank #23/70 · confidence 4 · eval date 2026-04-23

API audit comparison

Latest completed audits from shared providers, with four safety and integrity score groups plus report links.

Provider
GPT-5.1
GPT-5.5
No completed audits are available from shared providers yet.

Provider examples

Speed aggregates and input/output pricing share each provider row for real API selection and migration cost checks.

Provider
GPT-5.1
GPT-5.5
6345ywz API35 tests

GPT-5.1

speed / latency

N/A / N/A

input / output

No data

GPT-5.5

speed / latency

38 tok/s / 8937ms

input / output

No data

9527 API10 tests

GPT-5.1

speed / latency

N/A / N/A

input / output

No data

GPT-5.5

speed / latency

52 tok/s / 2732ms

input / output

No data

BUZZ10 tests

GPT-5.1

speed / latency

137 tok/s / 3299ms

input / output

No data

GPT-5.5

speed / latency

N/A / N/A

input / output

No data

DeepKey API10 tests

GPT-5.1

speed / latency

N/A / N/A

input / output

No data

GPT-5.5

speed / latency

43 tok/s / 2874ms

input / output

No data

Fengsili API5 tests

GPT-5.1

speed / latency

N/A / N/A

input / output

No data

GPT-5.5

speed / latency

58 tok/s / 3313ms

input / output

No data

兔子API

GPT-5.1

gpt-5.1-all

speed / latency

No data

input / output

$0/request

GPT-5.5

gpt-5.5-high

speed / latency

No data

input / output

$0/request

初叶🍂Furry API

GPT-5.1

gpt-5-1

speed / latency

No data

input / output

$0/request

GPT-5.5

gpt-5-5

speed / latency

No data

input / output

$0/request

Yun API

GPT-5.1

gpt-5.1

speed / latency

No data

input / output

$0.0014/request

GPT-5.5

gpt-5.5

speed / latency

No data

input / output

$0.171/M/$1.03/M

KFCV50

GPT-5.1

gpt-5.1

speed / latency

No data

input / output

$0.0068/request

GPT-5.5

gpt-5.5-low

speed / latency

No data

input / output

$0.342/M/$2.05/M

Jeniya AI API

GPT-5.1

gpt-5.1

speed / latency

No data

input / output

$0.014/M/$0.109/M

GPT-5.5

gpt-5.5

speed / latency

No data

input / output

$0.055/M/$0.327/M

FAQ

Weighted outcome: GPT-5.5. Benchmark capability categories carry 80%, while price, API performance, and availability carry 20%.

Why is this comparison indexable?
It has 6 verifiable comparison points, and both models have pricing or benchmark data.
Are missing metrics invented?
No. Metrics without LMSpeed data are omitted from this report.

Rankings are based on community-submitted tests and periodic health probes. Advisory only, not official data.