The Known Good Updated 2 Sep 2026 Subscribe
OpenAI: GPT-5.1 vs OpenAI: GPT-5.5 ·OpenAI vs OpenAI

OpenAI: GPT-5.1 vs OpenAI: GPT-5.5 — head-to-head comparison

OpenAI: GPT-5.1 profile OpenAI: GPT-5.5 profile All comparisons
OpenAI: GPT-5.1 — OpenAI
Quality
#23 of 65
75based on 6 of 7 evaluations
Known Good Index
Speed
#191 of 339
43.3
Output tokens per second
Price
#341 of 439
$3.44
Blended per 1M tokens
In $1.25 · Out $10.00
Cache hit price
#176 of 322
$0.12
per 1M tokens (−90%)
Context
#169 of 473
400k
tokens (~600 pages)
OpenAI: GPT-5.5 — OpenAI
Quality
#5 of 65
93based on 3 of 7 evaluations
Known Good Index
Speed
#65 of 339
85.0
Output tokens per second
Price
#412 of 439
$11.25
Blended per 1M tokens
In $5.00 · Out $30.00
Cache hit price
#295 of 322
$0.50
per 1M tokens (−90%)
Context
#30 of 473
1.05M
tokens (~1,600 pages)
Summary

On the Known Good Index, OpenAI: GPT-5.1 scores 75 and OpenAI: GPT-5.5 scores 93 — a 19-point lead for OpenAI: GPT-5.5. They share 3 published evaluations, with OpenAI: GPT-5.1 ahead on 1 and OpenAI: GPT-5.5 ahead on 2.

Blended pricing is $3.44 per 1M tokens for OpenAI: GPT-5.1 and $11.25 for OpenAI: GPT-5.5 — OpenAI: GPT-5.1 is about 3.3× cheaper.

Throughput is 43 tokens per second for OpenAI: GPT-5.1 and 85 for OpenAI: GPT-5.5, with time to first token at 1.2s and 4.9s. OpenAI: GPT-5.1 accepts 400k tokens of context against 1.05M.

OpenAI: GPT-5.1 is proprietary; OpenAI: GPT-5.5 is proprietary. 3 tracked hosts serve one or both, and 2 serve both.

Generated from tracked data on 3 Sep 2026 · how these comparisons are computed →

At a glance
MetricOpenAI: GPT-5.1OpenAI: GPT-5.5
Known Good Index 75 based on 6 of 7 evaluations 93 based on 3 of 7 evaluations
Blended $/1M $3.44 $11.25
Output tok/s 43 85
Context window 400k 1.05M
Providers 2 3
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Quality

Known Good Index and the capability indices, side by side

Index scores

Each index is min-max normalised across tracked models and scaled 0–100 from published evaluations. We do not run these evaluations.

MetricOpenAI: GPT-5.1OpenAI: GPT-5.5
Known Good Index 75 93
Coding Index 69 —
Reasoning Index 80 —
Openness Index 5 5
The Known Good

Quality Breakdown

Every evaluation both models report a published score for

Evaluations both models report

Bar = OpenAI: GPT-5.1 · marker = OpenAI: GPT-5.5 · scores ingested from Epoch AI (CC-BY 4.0)

GPQA Diamond88 / 91
Mock AIME 2024–2589 / 84
Terminal-Bench48 / 85

Right-hand figures read OpenAI: GPT-5.1 / OpenAI: GPT-5.5. OpenAI: GPT-5.1 leads on 1 of 3, OpenAI: GPT-5.5 on 2.

The Known Good

Arena Elo

Human preference rating from blind pairwise votes

Arena ratings

Elo from blind pairwise votes, ingested from Arena. Higher is better.

MetricOpenAI: GPT-5.1OpenAI: GPT-5.5
Text Arena 1,422 1,467
Text Arena (style controlled) 1,439 1,477
The Known Good

Price & Cost

Published API pricing by token type

Published pricing

USD per 1M tokens. Blended is a 3:1 input:output mix. Live from OpenRouter, cross-checked against models.dev. Lower is better.

MetricOpenAI: GPT-5.1OpenAI: GPT-5.5
Input $/1M $1.25 $5.00
Output $/1M $10.00 $30.00
Blended $/1M $3.44 $11.25
Cache read $/1M $0.125 $0.500
The Known Good
We publish blended price rather than cost-per-task. Cost-per-task requires token counts from an evaluation suite we do not run. Blended price is computed from published rates and is fully reproducible — see the pricing methodology.

Context Window

Maximum input accepted and maximum output emitted

Context and output limits

Provider-declared limits, from metadata via models.dev and OpenRouter. Higher is better.

MetricOpenAI: GPT-5.1OpenAI: GPT-5.5
Context window 400k 1.05M
Max output tokens 128k 128k
The Known Good

Speed & Latency

Mean throughput and time to first token across hosting providers, over successful measurements from the last 48 hours

Throughput and latency

Means across all tracked providers over successful measurements from the last 48 hours, derived from OpenRouter endpoint telemetry.

MetricOpenAI: GPT-5.1OpenAI: GPT-5.5
Output tokens/s 43 85
Time to first token 1.2s 4.9s
The Known Good

Providers

Which hosts serve each model, and at what price and speed

3 hosts · 2 serve both
Full provider benchmarks →
Provider OpenAI: GPT-5.1 blendedOpenAI: GPT-5.1 tok/s OpenAI: GPT-5.5 blendedOpenAI: GPT-5.5 tok/s
OpenAI · first party $1.72 73 $5.62 70
Azure · first party $3.44 39 $11.25 54
Amazon Bedrock · first party — — $12.38 180

Per-host pricing and telemetry from OpenRouter. A dash means that host does not serve that model.

The Known Good
Sources for this page
Pricing & providers — OpenRouter Metadata — models.dev Benchmarks — Epoch AI (CC-BY 4.0)Elo — Arena Full attribution →