Gemini 3.5 Flash vs Grok 4.20

Gemini 3.5 Flash leads Grok 4.20 on coding, 39.8 to 33.3 on the Vibe Coding Index, and Grok 4.20 costs 3.6x less per output token ($2.50 vs $9.00 per million). Updated October 21, 2026; 48 benchmarks have a result for both.

Replace Gemini 3.5 Flash Replace Grok 4.20

Gemini 3.5 FlashGoogle

Coding: 39.8
Overall: 63.8
Output $/M: $9.00

Grok 4.20xAI

Coding: 33.3
Overall: 41.0
Output $/M: $2.50

vs boards won of 48 shared

Gemini 3.5 Flash or Grok 4.20: which to pick

Pick Gemini 3.5 Flash for coding: it scores 39.8 on the Vibe Coding Index against 33.3 for Grok 4.20.

Pick Grok 4.20 for output tokens 3.6x cheaper ($2.50 vs $9.00 per million) and a lower cost per solved task ($0.72 against $1.21).

Model AGemini 3.5 FlashGoogle39.8/1004 independent benchmarks$1.21 per solved task Model BGrok 4.20xAI33.3/1002 independent benchmarks$0.72 per solved task

48647

Shared results: 48
Gemini 3.5 Flash only: 64
Grok 4.20 only: 7
Like-for-like categories: 7 of 9

Only benchmarks that tested both models count toward a pick; a result only one model has is shown but not compared.

Which one for your work

Each card is decided by one number both models carry. Where only one has it, the card says so and makes no call.

Coding
Vibe Coding Index, six public coding benchmarks
Gemini 3.5 Flash
Gemini 3.5 Flash scores 39.8 against 33.3.
4 and 2 benchmarks behind the scores
Intelligence
AA Intelligence Index
Gemini 3.5 Flash
Gemini 3.5 Flash leads, 33.6 against 25.7.
Same board, both measured
Reasoning
GPQA Diamond
Gemini 3.5 Flash
Gemini 3.5 Flash leads, 92.7% against 88.6%.
Same board, both measured
Math
AIME
No call
Only Grok 4.20 has a AIME result, 96.5%.
Directional only
Knowledge
MMLU Pro
Gemini 3.5 Flash
Gemini 3.5 Flash leads, 89.5% against 86.3%.
Same board, both measured
Web design
Design Arena: websites
Gemini 3.5 Flash
Gemini 3.5 Flash leads, 1268 against 1229.
Same board, both measured
Long documents
Listed context window
Grok 4.20
Grok 4.20 takes 2M tokens against 1.05M.
Listed by OpenRouter
Everyday cost
1K input + 500 output tokens
Grok 4.20
Gemini 3.5 Flash $0.0060, Grok 4.20 $0.0025 per turn.
List prices
Cost per solved task
One SWE-bench Verified task, solved
Grok 4.20
Gemini 3.5 Flash $1.21, Grok 4.20 $0.72.
Published attempt cost and pass rate

At a glance

Coding index: Gemini 3.5 Flash 39.8 from 4 benchmarks, Grok 4.20 33.3 from 2 benchmarks.
Widest category: Coding, 18.5 points apart on average over 7 shared benchmarks.
Widest single gap: Excel Modeling Benchmark (Vals AI): Gemini 3.5 Flash 63.5% against Grok 4.20 11.7%, 51.8 points apart on a 0 to 100 scale.
Output price: Gemini 3.5 Flash $9.00 against Grok 4.20 $2.50 per million output tokens, 3.6x apart.
Context window: Gemini 3.5 Flash takes 1.05M tokens, Grok 4.20 2M.

Benchmark by benchmark

First the score: boards each model leads, per category, where both have a result. Then every board, a category to a fold; bars are each result on a 0 to 100 scale, so compare the two in a row, not one row with another.

Boards won, where both have a result
Category	Gemini 3.5 Flash	Grok 4.20
Coding	7	0
Intelligence	2	0
Agentic work	11	1
Reasoning	6	0
Knowledge	6	0
Web design	8	0
General	6	1
All shared boards	46	2

CodingLike-for-likeSix of these boards feed the Vibe Coding Index70

Coding benchmarks for Gemini 3.5 Flash and Grok 4.20
Benchmark	Gemini 3.5 Flash	Grok 4.20	Leader
LMArena WebDev	1499	Not measured	Only Gemini 3.5 Flash measured
LiveCodeBench (Vals AI)	87.6%	84.3%	Gemini 3.5 Flash
SWE-bench Verified (Vals AI)	78.8%	72.2%	Gemini 3.5 Flash
Terminal-Bench 4 (Vals AI)	6.1%	Not measured	Only Gemini 3.5 Flash measured
Vibe Code Bench (Vals AI)	48.7%	4.1%	Gemini 3.5 Flash
Code migration (Vals AI)	26.8%	0.3%	Gemini 3.5 Flash
ProgramBench (Vals AI)	0.0%	Not measured	Only Gemini 3.5 Flash measured
Terminal-Bench 2.1 (Vals AI)	74.2%	44.2%	Gemini 3.5 Flash
SkillsBench (Vals AI)	52.7%	Not measured	Only Gemini 3.5 Flash measured
SciCode	53.9%	Not measured	Only Gemini 3.5 Flash measured
Terminal-Bench Hard (Artificial Analysis run)	46.2%	37.9%	Gemini 3.5 Flash
Terminal-Bench	Not measured	57.3%	Only Grok 4.20 measured
WeirdML	62.6%	52.3%	Gemini 3.5 Flash
ALE-Bench	911.0	Not measured	Only Gemini 3.5 Flash measured
LMArena Text: coding	1493	Not measured	Only Gemini 3.5 Flash measured
LMArena Text: software and IT	1494	Not measured	Only Gemini 3.5 Flash measured
LMArena WebDev: React	1495	Not measured	Only Gemini 3.5 Flash measured
LMArena WebDev: HTML	1522	Not measured	Only Gemini 3.5 Flash measured
LMArena WebDev: from an image	1504	Not measured	Only Gemini 3.5 Flash measured
SciCode	12.3%	Not measured	Only Gemini 3.5 Flash measured
Neither model has a result on the other 19 boards here

IntelligenceLike-for-likePublic boards, shown as published, kept out of the index20

Intelligence benchmarks for Gemini 3.5 Flash and Grok 4.20
Benchmark	Gemini 3.5 Flash	Grok 4.20	Leader
AA Intelligence Index	33.6	25.7	Gemini 3.5 Flash
Epoch Capabilities Index	154.9	152.1	Gemini 3.5 Flash

Agentic workLike-for-likePublic boards, shown as published, kept out of the index111

Agentic work benchmarks for Gemini 3.5 Flash and Grok 4.20
Benchmark	Gemini 3.5 Flash	Grok 4.20	Leader
Design Arena: agents building web apps	1202	1144	Gemini 3.5 Flash
Design Arena: agents building full-stack apps	1197	1054	Gemini 3.5 Flash
Design Arena: agents building mobile apps	1174	1090	Gemini 3.5 Flash
Design Arena: agents building Android apps	1184	1052	Gemini 3.5 Flash
Design Arena: agents building Godot games	1098	1089	Gemini 3.5 Flash
Design Arena: agents building games	1180	Not measured	Only Gemini 3.5 Flash measured
Design Arena: HTML slides	1142	1180	Grok 4.20
Design Arena: PowerPoint slides	1179	Not measured	Only Gemini 3.5 Flash measured
Finance Agent (Vals AI)	57.9%	28.5%	Gemini 3.5 Flash
Tax Agent Bench (Vals AI)	21.6%	7.0%	Gemini 3.5 Flash
Legal Research Bench (Vals AI)	30.8%	13.9%	Gemini 3.5 Flash
Excel Modeling Benchmark (Vals AI)	63.5%	11.7%	Gemini 3.5 Flash
Terminal-Bench-Science (Vals AI)	5.7%	Not measured	Only Gemini 3.5 Flash measured
τ²-Bench Telecom	95.6%	93.0%	Gemini 3.5 Flash
APEX-Agents	27.5%	Not measured	Only Gemini 3.5 Flash measured
Vending-Bench 2	$5,396	$4,663	Gemini 3.5 Flash
Neither model has a result on the other 25 boards here

ReasoningLike-for-likePublic boards, shown as published, kept out of the index60

Reasoning benchmarks for Gemini 3.5 Flash and Grok 4.20
Benchmark	Gemini 3.5 Flash	Grok 4.20	Leader
GPQA Diamond	92.7%	88.6%	Gemini 3.5 Flash
MMMU Pro (Vals AI)	88.3%	83.5%	Gemini 3.5 Flash
GPQA Diamond (Artificial Analysis run)	92.2%	91.1%	Gemini 3.5 Flash
Humanity's Last Exam (Artificial Analysis run)	42.7%	34.5%	Gemini 3.5 Flash
GPQA Diamond (Epoch AI run)	92.8%	Not measured	Only Gemini 3.5 Flash measured
ARC-AGI	92.5%	89.5%	Gemini 3.5 Flash
ARC-AGI-2	72.1%	65.1%	Gemini 3.5 Flash
SimpleBench	76.7%	Not measured	Only Gemini 3.5 Flash measured
Chess puzzles	45.0%	Not measured	Only Gemini 3.5 Flash measured
Mystery game puzzles	32.0%	Not measured	Only Gemini 3.5 Flash measured
EBR-bench	4.8%	Not measured	Only Gemini 3.5 Flash measured
LMArena Text: hard prompts	1488	Not measured	Only Gemini 3.5 Flash measured
LMArena Text: expert	1495	Not measured	Only Gemini 3.5 Flash measured
LMArena Text: hard prompts in English	1483	Not measured	Only Gemini 3.5 Flash measured
LMArena Vision: diagrams	1323	Not measured	Only Gemini 3.5 Flash measured
LMArena Vision: homework	1330	Not measured	Only Gemini 3.5 Flash measured
Kagi LLM Benchmark	Not measured	75.0%	Only Grok 4.20 measured
Neither model has a result on the other 5 boards here

MathDirectional onlyPublic boards, shown as published, kept out of the index7 boards, none shared

Math benchmarks for Gemini 3.5 Flash and Grok 4.20
Benchmark	Gemini 3.5 Flash	Grok 4.20	Leader
AIME	Not measured	96.5%	Only Grok 4.20 measured
OTIS Mock AIME	95.6%	Not measured	Only Gemini 3.5 Flash measured
FrontierMath, tiers 1 to 3	62.8%	Not measured	Only Gemini 3.5 Flash measured
FrontierMath, tier 4	26.8%	Not measured	Only Gemini 3.5 Flash measured
ProofBench	31.0%	Not measured	Only Gemini 3.5 Flash measured
LMArena Text: math	1504	Not measured	Only Gemini 3.5 Flash measured
LMArena Text: mathematical work	1495	Not measured	Only Gemini 3.5 Flash measured
Neither model has a result on the other 6 boards here

KnowledgeLike-for-likePublic boards, shown as published, kept out of the index60

Knowledge benchmarks for Gemini 3.5 Flash and Grok 4.20
Benchmark	Gemini 3.5 Flash	Grok 4.20	Leader
MMLU Pro	89.5%	86.3%	Gemini 3.5 Flash
LegalBench (Vals AI)	83.6%	77.7%	Gemini 3.5 Flash
CaseLaw (Vals AI)	Not measured	54.4%	Only Grok 4.20 measured
CorpFin (Vals AI)	64.7%	63.7%	Gemini 3.5 Flash
TaxEval (Vals AI)	74.4%	74.1%	Gemini 3.5 Flash
MortgageTax (Vals AI)	68.1%	45.4%	Gemini 3.5 Flash
MedQA (Vals AI)	Not measured	94.5%	Only Grok 4.20 measured
MedCode (Vals AI)	55.8%	32.2%	Gemini 3.5 Flash
SimpleQA Verified	66.2%	Not measured	Only Gemini 3.5 Flash measured
LMArena Text: science	1495	Not measured	Only Gemini 3.5 Flash measured
LMArena Text: medicine and healthcare	1483	Not measured	Only Gemini 3.5 Flash measured
LMArena Text: legal and government	1488	Not measured	Only Gemini 3.5 Flash measured
LMArena Text: business and finance	1467	Not measured	Only Gemini 3.5 Flash measured
FACTS Benchmark Suite	63.1%	Not measured	Only Gemini 3.5 Flash measured
Neither model has a result on the other 4 boards here

Web designLike-for-likePublic boards, shown as published, kept out of the index80

Web design benchmarks for Gemini 3.5 Flash and Grok 4.20
Benchmark	Gemini 3.5 Flash	Grok 4.20	Leader
Design Arena: websites	1268	1229	Gemini 3.5 Flash
Design Arena: UI components	1273	1199	Gemini 3.5 Flash
Design Arena: game dev	1263	1192	Gemini 3.5 Flash
Design Arena: data viz	1236	1217	Gemini 3.5 Flash
Design Arena: 3D	1244	1193	Gemini 3.5 Flash
Design Arena: all code categories	1266	1221	Gemini 3.5 Flash
Design Arena: SVG	1254	1164	Gemini 3.5 Flash
Design Arena: ASCII art	1254	1174	Gemini 3.5 Flash
Neither model has a result on the other 1 board here

GeneralLike-for-likePublic boards, shown as published, kept out of the index61

General benchmarks for Gemini 3.5 Flash and Grok 4.20
Benchmark	Gemini 3.5 Flash	Grok 4.20	Leader
Public Benefits Bench (Vals AI)	59.5%	Not measured	Only Gemini 3.5 Flash measured
SAGE (Vals AI)	49.9%	38.2%	Gemini 3.5 Flash
MedScribe (Vals AI)	76.6%	63.4%	Gemini 3.5 Flash
Vals Multimodal Index	62.9%	39.1%	Gemini 3.5 Flash
IFBench	76.3%	81.2%	Grok 4.20
Long context reasoning (AA-LCR)	74.3%	69.0%	Gemini 3.5 Flash
DTBench	94.7%	90.1%	Gemini 3.5 Flash
LMCA	47.1%	38.7%	Gemini 3.5 Flash
CL-bench	Not measured	22.2%	Only Grok 4.20 measured
Surface Evolver Bench	58.1%	Not measured	Only Gemini 3.5 Flash measured
CL-bench Life	Not measured	11.9%	Only Grok 4.20 measured
LMArena Text	1482	Not measured	Only Gemini 3.5 Flash measured
LMArena Text: instruction following	1467	Not measured	Only Gemini 3.5 Flash measured
LMArena Text: creative writing	1470	Not measured	Only Gemini 3.5 Flash measured
LMArena Vision	1308	Not measured	Only Gemini 3.5 Flash measured
LMArena Text: English	1481	Not measured	Only Gemini 3.5 Flash measured
LMArena Text: non-English	1475	Not measured	Only Gemini 3.5 Flash measured
LMArena Text: Chinese	1527	Not measured	Only Gemini 3.5 Flash measured
LMArena Text: German	1494	Not measured	Only Gemini 3.5 Flash measured
LMArena Text: Japanese	1486	Not measured	Only Gemini 3.5 Flash measured
LMArena Text: Korean	1448	Not measured	Only Gemini 3.5 Flash measured
LMArena Text: French	1490	Not measured	Only Gemini 3.5 Flash measured
LMArena Text: Spanish	1480	Not measured	Only Gemini 3.5 Flash measured
LMArena Text: Russian	1493	Not measured	Only Gemini 3.5 Flash measured
LMArena Text: Polish	1516	Not measured	Only Gemini 3.5 Flash measured
LMArena Text: multi-turn	1481	Not measured	Only Gemini 3.5 Flash measured
LMArena Text: longer queries	1483	Not measured	Only Gemini 3.5 Flash measured
LMArena Text: writing and language	1478	Not measured	Only Gemini 3.5 Flash measured
LMArena Text: entertainment and media	1459	Not measured	Only Gemini 3.5 Flash measured
LMArena Vision: English	1305	Not measured	Only Gemini 3.5 Flash measured
LMArena Vision: Chinese	1377	Not measured	Only Gemini 3.5 Flash measured
LMArena Vision: reading text	1317	Not measured	Only Gemini 3.5 Flash measured
LMArena Vision: humor	1321	Not measured	Only Gemini 3.5 Flash measured
LMArena Vision: creative writing	1301	Not measured	Only Gemini 3.5 Flash measured
LMArena Document	1463	Not measured	Only Gemini 3.5 Flash measured
Neither model has a result on the other 11 boards here

Image generationNot comparablePublic boards, shown as published, kept out of the index0 boards, none shared

Image generation benchmarks for Gemini 3.5 Flash and Grok 4.20
Benchmark	Gemini 3.5 Flash	Grok 4.20	Leader
Neither model has a result on 5 boards here

What each workload costs

Three fixed token mixes at each model's listed price, so per-token rates become a bill.

Chat turn

1K input + 500 output tokens

Gemini 3.5 Flash$0.0060Fits in one request

Grok 4.20$0.0025Fits in one request

Grok 4.20 costs less

Repository review

50K input + 3K output tokens

Gemini 3.5 Flash$0.102Fits in one request

Grok 4.20$0.070Fits in one request

Grok 4.20 costs less

Agent loop

200K input + 10K output tokens

Gemini 3.5 Flash$0.390Fits in one request

Grok 4.20$0.275Fits in one request

Grok 4.20 costs less

Listed OpenRouter rates, without cache or batch discounts. A workload that does not fit a model's context window would need splitting.

Specification differences

The leading value in a row is marked; a row with a missing value names no leader. Our two rows are marked in red.

Specifications of Gemini 3.5 Flash and Grok 4.20
Specification	Google Gemini 3.5 Flash	SpaceXAI Grok 4.20
Maker	Google	xAI
Weights	No public weights listed	No public weights listed
Released	May 19, 2026	March 31, 2026
Context window	1.05M	2M
Input $/Mtok	$1.50	$1.25
Output $/Mtok	$9.00	$2.50
Coding index	39.8	33.3
Independent measurements behind it	4	2
Cost per solved task	$1.21	$0.72
Source	OpenRouter listing	OpenRouter listing

Questions

Is Gemini 3.5 Flash better than Grok 4.20 for coding?

Pick Gemini 3.5 Flash for coding: it scores 39.8 on the Vibe Coding Index against 33.3 for Grok 4.20. Pick Grok 4.20 for output tokens 3.6x cheaper ($2.50 vs $9.00 per million) and a lower cost per solved task ($0.72 against $1.21).

Which is cheaper, Gemini 3.5 Flash or Grok 4.20?

Gemini 3.5 Flash costs $1.50 per million input tokens and $9.00 per million output tokens; Grok 4.20 costs $1.25 and $2.50. Per solved SWE-bench Verified task, Gemini 3.5 Flash costs $1.21 and Grok 4.20 $0.72.

Which has the bigger context window, Gemini 3.5 Flash or Grok 4.20?

Grok 4.20, with 2M tokens against 1.05M.

How many benchmarks is the Gemini 3.5 Flash vs Grok 4.20 comparison based on?

48 benchmarks have a result for both models as of October 21, 2026. Gemini 3.5 Flash's coding index rests on 4 independent benchmarks and Grok 4.20's on 2. Where only one model has a result, the page says so instead of naming a winner.

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<iframe src="https://llmbenchmark.ai/embed/compare/gemini-3-5-flash-vs-grok-4-20" title="Gemini 3.5 Flash vs Grok 4.20, LLMBenchmark.ai" width="100%" height="360" style="border:0;max-width:100%" loading="lazy"></iframe>
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Gemini 3.5 Flash or Grok 4.20: which to pick

Which one for your work

Coding

Intelligence

Reasoning

Math

Knowledge

Web design

Long documents

Everyday cost

Cost per solved task

At a glance

Benchmark by benchmark

What each workload costs

Chat turn

Repository review

Agent loop

Specification differences

Questions

Compare next