The Known Good Updated 29 Jul 2026
Google: Gemini 3.5 Flash vs OpenAI: GPT-5.1 ·Google vs OpenAI

Google: Gemini 3.5 Flash vs OpenAI: GPT-5.1 — head-to-head comparison

Google: Gemini 3.5 Flash profile OpenAI: GPT-5.1 profile All comparisons
Google: Gemini 3.5 Flash — Google
Quality
#3 of 62
95based on 3 of 7 evaluations
Known Good Index
Speed
#25 of 317
126.1
Output tokens per second
Price
#281 of 370
$3.38
Blended per 1M tokens
In $1.50 · Out $9.00
Cache hit price
#153 of 238
$0.15
per 1M tokens (−90%)
Context
#58 of 375
1.05M
tokens (~1,600 pages)
OpenAI: GPT-5.1 — OpenAI
Quality
#24 of 62
74based on 6 of 7 evaluations
Known Good Index
Speed
#140 of 317
52.6
Output tokens per second
Price
#282 of 370
$3.44
Blended per 1M tokens
In $1.25 · Out $10.00
Cache hit price
#122 of 238
$0.12
per 1M tokens (−90%)
Context
#115 of 375
400k
tokens (~600 pages)
Summary

On the Known Good Index, Google: Gemini 3.5 Flash scores 95 and OpenAI: GPT-5.1 scores 74 — a 21-point lead for Google: Gemini 3.5 Flash. They share 3 published evaluations, with Google: Gemini 3.5 Flash ahead on 3 and OpenAI: GPT-5.1 ahead on 0.

Blended pricing is $3.38 per 1M tokens for Google: Gemini 3.5 Flash and $3.44 for OpenAI: GPT-5.1, within 10% of each other.

Throughput is 126 tokens per second for Google: Gemini 3.5 Flash and 53 for OpenAI: GPT-5.1, with time to first token at 1.8s and 1.2s. Google: Gemini 3.5 Flash accepts 1.05M tokens of context against 400k.

Google: Gemini 3.5 Flash is proprietary; OpenAI: GPT-5.1 is proprietary. 4 tracked hosts serve one or both.

Generated from tracked data on 29 Jul 2026 · how these comparisons are computed →

At a glance
MetricGoogle: Gemini 3.5 FlashOpenAI: GPT-5.1
Known Good Index 95 based on 3 of 7 evaluations 74 based on 6 of 7 evaluations
Blended $/1M $3.38 $3.44
Output tok/s 126 53
Context window 1.05M 400k
Providers 2 2
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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.

MetricGoogle: Gemini 3.5 FlashOpenAI: GPT-5.1
Known Good Index 95 74
Coding Index — 68
Mathematics Index 96 89
Reasoning Index — 80
Agentic Index 92 61
Openness Index 5 5
The Known Good

Quality Breakdown

Every evaluation both models report a published score for

Evaluations both models report

Bar = Google: Gemini 3.5 Flash · marker = OpenAI: GPT-5.1 · scores ingested from Epoch AI (CC-BY 4.0)

GPQA Diamond93 / 88
Mock AIME 2024–2596 / 89
SWE-bench Verified79 / 68

Right-hand figures read Google: Gemini 3.5 Flash / OpenAI: GPT-5.1. Google: Gemini 3.5 Flash leads on 3 of 3, OpenAI: GPT-5.1 on 0.

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.

MetricGoogle: Gemini 3.5 FlashOpenAI: GPT-5.1
Text Arena — 1,422
Text Arena (style controlled) — 1,439
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.

MetricGoogle: Gemini 3.5 FlashOpenAI: GPT-5.1
Input $/1M $1.50 $1.25
Output $/1M $9.00 $10.00
Blended $/1M $3.38 $3.44
Cache read $/1M $0.150 $0.125
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.

MetricGoogle: Gemini 3.5 FlashOpenAI: GPT-5.1
Context window 1.05M 400k
Max output tokens 66k 128k
The Known Good

Speed & Latency

Median throughput and time to first token across hosting providers

Output speedTime to first token
Throughput and latency

Medians across all tracked providers, derived from OpenRouter endpoint telemetry.

MetricGoogle: Gemini 3.5 FlashOpenAI: GPT-5.1
Output tokens/s 126 53
Time to first token 1.8s 1.2s
The Known Good

Providers

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

4 hosts
Full provider benchmarks →
Provider Google: Gemini 3.5 Flash blendedGoogle: Gemini 3.5 Flash tok/s OpenAI: GPT-5.1 blendedOpenAI: GPT-5.1 tok/s
Google AI Studio $1.69 191 — —
Google · first party $1.69 108 — —
Azure · first party — — $3.44 66
OpenAI · first party — — $1.72 44

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 →