Gemini 3.8 Flash vs Grok 4.20

Gemini 3.8 Flash leads Grok 4.20 on coding, 61.6 to 33.3 on the Vibe Coding Index, and Grok 4.20 costs 1.5x less per output token ($2.50 vs $3.75 per million). Updated October 21, 2026; 42 benchmarks have a result for both.

Replace Gemini 3.8 Flash Replace Grok 4.20

Gemini 3.8 FlashGoogle

Coding: 61.6
Overall: 69.0
Output $/M: $3.75

Grok 4.20xAI

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

vs boards won of 42 shared

Gemini 3.8 Flash or Grok 4.20: which to pick

Pick Gemini 3.8 Flash for coding: it scores 61.6 on the Vibe Coding Index against 33.3 for Grok 4.20.

Pick Grok 4.20 for output tokens 1.5x cheaper ($2.50 vs $3.75 per million) and a lower cost per solved task ($0.72 against $2.74).

Model AGemini 3.8 FlashGoogle61.6/1006 independent benchmarks$2.74 per solved task Model BGrok 4.20xAI33.3/1002 independent benchmarks$0.72 per solved task

428613

Shared results: 42
Gemini 3.8 Flash only: 86
Grok 4.20 only: 13
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 3.8 Flash
Gemini 3.8 Flash scores 61.6 against 33.3.
6 and 2 benchmarks behind the scores
Intelligence
AA Intelligence Index
Gemini 3.8 Flash
Gemini 3.8 Flash leads, 40.9 against 25.7.
Same board, both measured
Agentic work
AA Agentic Index
No call
Only Gemini 3.8 Flash has a AA Agentic Index result, 40.2.
Directional only
Reasoning
GPQA Diamond
Gemini 3.8 Flash
Gemini 3.8 Flash leads, 94.4% 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 3.8 Flash
Gemini 3.8 Flash leads, 90.2% against 86.3%.
Same board, both measured
Web design
Design Arena: websites
Gemini 3.8 Flash
Gemini 3.8 Flash leads, 1300 against 1229.
Same board, both measured
General
Vals Index
No call
Only Gemini 3.8 Flash has a Vals Index result, 56.0%.
Directional only
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 3.8 Flash $0.0026, Grok 4.20 $0.0025 per turn.
List prices
Cost per solved task
One SWE-bench Verified task, solved
Grok 4.20
Gemini 3.8 Flash $2.74, Grok 4.20 $0.72.
Published attempt cost and pass rate

At a glance

Coding index: Gemini 3.8 Flash 61.6 from 6 benchmarks, Grok 4.20 33.3 from 2 benchmarks.
Widest category: Coding, 32.2 points apart on average over 6 shared benchmarks.
Widest single gap: Vibe Code Bench (Vals AI): Gemini 3.8 Flash 78.7% against Grok 4.20 4.1%, 74.6 points apart on a 0 to 100 scale.
Output price: Gemini 3.8 Flash $3.75 against Grok 4.20 $2.50 per million output tokens, 1.5x apart.
Context window: Gemini 3.8 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 3.8 Flash	Grok 4.20
Coding	6	0
Intelligence	2	0
Agentic work	10	0
Reasoning	6	0
Knowledge	5	0
Web design	8	0
General	4	1
All shared boards	41	1

CodingLike-for-likeSix of these boards feed the Vibe Coding Index60

Coding benchmarks for Gemini 3.8 Flash and Grok 4.20
Benchmark	Gemini 3.8 Flash	Grok 4.20	Leader
LiveBench coding	82.2%	Not measured	Only Gemini 3.8 Flash measured
LMArena WebDev	1585	Not measured	Only Gemini 3.8 Flash measured
AA Coding Index	76.3	Not measured	Only Gemini 3.8 Flash measured
LiveCodeBench (Vals AI)	89.5%	84.3%	Gemini 3.8 Flash
SWE-bench Verified (Vals AI)	80.0%	72.2%	Gemini 3.8 Flash
Terminal-Bench 4 (Vals AI)	19.7%	Not measured	Only Gemini 3.8 Flash measured
Vibe Code Bench (Vals AI)	78.7%	4.1%	Gemini 3.8 Flash
Code migration (Vals AI)	36.5%	0.3%	Gemini 3.8 Flash
ProgramBench (Vals AI)	1.0%	Not measured	Only Gemini 3.8 Flash measured
IOI (Vals AI)	56.9%	Not measured	Only Gemini 3.8 Flash measured
Terminal-Bench 2.1 (Vals AI)	81.3%	44.2%	Gemini 3.8 Flash
SWE-bench Multimodal (Vals AI)	40.8%	Not measured	Only Gemini 3.8 Flash measured
Vibe Code Bench 1-100 (Vals AI)	18.8%	Not measured	Only Gemini 3.8 Flash measured
SkillsBench (Vals AI)	58.0%	Not measured	Only Gemini 3.8 Flash measured
CyberBench (Vals AI)	43.8%	Not measured	Only Gemini 3.8 Flash measured
SciCode	56.6%	Not measured	Only Gemini 3.8 Flash measured
Terminal-Bench Hard (Artificial Analysis run)	Not measured	37.9%	Only Grok 4.20 measured
Terminal-Bench	Not measured	57.3%	Only Grok 4.20 measured
FrontierCode	41.2%	Not measured	Only Gemini 3.8 Flash measured
FrontierSWE	19.6%	Not measured	Only Gemini 3.8 Flash measured
WeirdML	84.8%	52.3%	Gemini 3.8 Flash
ALE-Bench	1269.7	Not measured	Only Gemini 3.8 Flash measured
LMArena Text: coding	1508	Not measured	Only Gemini 3.8 Flash measured
LMArena Text: software and IT	1507	Not measured	Only Gemini 3.8 Flash measured
LMArena WebDev: React	1577	Not measured	Only Gemini 3.8 Flash measured
LMArena WebDev: HTML	1616	Not measured	Only Gemini 3.8 Flash measured
LMArena WebDev: from an image	1593	Not measured	Only Gemini 3.8 Flash measured
SciCode	12.3%	Not measured	Only Gemini 3.8 Flash measured
Neither model has a result on the other 11 boards here

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

Intelligence benchmarks for Gemini 3.8 Flash and Grok 4.20
Benchmark	Gemini 3.8 Flash	Grok 4.20	Leader
AA Intelligence Index	40.9	25.7	Gemini 3.8 Flash
Epoch Capabilities Index	157.4	152.1	Gemini 3.8 Flash

Agentic workLike-for-likePublic boards, shown as published, kept out of the index100

Agentic work benchmarks for Gemini 3.8 Flash and Grok 4.20
Benchmark	Gemini 3.8 Flash	Grok 4.20	Leader
AA Agentic Index	40.2	Not measured	Only Gemini 3.8 Flash measured
Design Arena: agents building web apps	1238	1144	Gemini 3.8 Flash
Design Arena: agents building full-stack apps	1244	1054	Gemini 3.8 Flash
Design Arena: agents building mobile apps	1236	1090	Gemini 3.8 Flash
Design Arena: agents building Android apps	1074	1052	Gemini 3.8 Flash
Design Arena: agents building Godot games	1273	1089	Gemini 3.8 Flash
Design Arena: HTML slides	Not measured	1180	Only Grok 4.20 measured
Design Arena: PowerPoint slides	1177	Not measured	Only Gemini 3.8 Flash measured
Design Arena: spreadsheets	1056	Not measured	Only Gemini 3.8 Flash measured
LiveBench research	79.1%	Not measured	Only Gemini 3.8 Flash measured
LiveBench browser	64.0%	Not measured	Only Gemini 3.8 Flash measured
LiveBench long agentic	30.1%	Not measured	Only Gemini 3.8 Flash measured
SREBench (Vals AI)	11.1%	Not measured	Only Gemini 3.8 Flash measured
Finance Agent (Vals AI)	61.4%	28.5%	Gemini 3.8 Flash
Tax Agent Bench (Vals AI)	32.1%	7.0%	Gemini 3.8 Flash
Legal Research Bench (Vals AI)	38.9%	13.9%	Gemini 3.8 Flash
Harvey's Legal Agent Benchmark (Vals AI)	12.1%	Not measured	Only Gemini 3.8 Flash measured
Excel Modeling Benchmark (Vals AI)	72.2%	11.7%	Gemini 3.8 Flash
BioMysteryBench (Vals AI)	62.2%	Not measured	Only Gemini 3.8 Flash measured
Terminal-Bench-Science (Vals AI)	8.6%	Not measured	Only Gemini 3.8 Flash measured
Vals Science Index	35.8%	Not measured	Only Gemini 3.8 Flash measured
Time Horizon Index (Vals AI)	18.8%	Not measured	Only Gemini 3.8 Flash measured
CUA-bench (Vals AI)	4.2%	Not measured	Only Gemini 3.8 Flash measured
τ²-Bench Telecom	Not measured	93.0%	Only Grok 4.20 measured
APEX-Agents	64.3%	Not measured	Only Gemini 3.8 Flash measured
Remote Labor Index	5.8%	Not measured	Only Gemini 3.8 Flash measured
Vending-Bench 2	$5,094	$4,663	Gemini 3.8 Flash
Neither model has a result on the other 14 boards here

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

Reasoning benchmarks for Gemini 3.8 Flash and Grok 4.20
Benchmark	Gemini 3.8 Flash	Grok 4.20	Leader
GPQA Diamond	94.4%	88.6%	Gemini 3.8 Flash
LiveBench reasoning	89.3%	Not measured	Only Gemini 3.8 Flash measured
MysteryMechanism (Vals AI)	36.5%	Not measured	Only Gemini 3.8 Flash measured
MMMU Pro (Vals AI)	89.1%	83.5%	Gemini 3.8 Flash
GPQA Diamond (Artificial Analysis run)	95.3%	91.1%	Gemini 3.8 Flash
Humanity's Last Exam (Artificial Analysis run)	47.8%	34.5%	Gemini 3.8 Flash
GPQA Diamond (Epoch AI run)	95.4%	Not measured	Only Gemini 3.8 Flash measured
ARC-AGI	98.5%	89.5%	Gemini 3.8 Flash
ARC-AGI-2	89.2%	65.1%	Gemini 3.8 Flash
Chess puzzles	58.0%	Not measured	Only Gemini 3.8 Flash measured
Mystery game puzzles	47.0%	Not measured	Only Gemini 3.8 Flash measured
LMArena Text: hard prompts	1509	Not measured	Only Gemini 3.8 Flash measured
LMArena Text: expert	1526	Not measured	Only Gemini 3.8 Flash measured
LMArena Text: hard prompts in English	1504	Not measured	Only Gemini 3.8 Flash measured
LMArena Vision: diagrams	1345	Not measured	Only Gemini 3.8 Flash measured
LMArena Vision: homework	1351	Not measured	Only Gemini 3.8 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 3.8 Flash and Grok 4.20
Benchmark	Gemini 3.8 Flash	Grok 4.20	Leader
AIME	Not measured	96.5%	Only Grok 4.20 measured
OTIS Mock AIME	98.9%	Not measured	Only Gemini 3.8 Flash measured
FrontierMath, tiers 1 to 3	68.4%	Not measured	Only Gemini 3.8 Flash measured
FrontierMath, tier 4	22.0%	Not measured	Only Gemini 3.8 Flash measured
ProofBench	48.0%	Not measured	Only Gemini 3.8 Flash measured
LMArena Text: math	1532	Not measured	Only Gemini 3.8 Flash measured
LMArena Text: mathematical work	1519	Not measured	Only Gemini 3.8 Flash measured
Neither model has a result on the other 6 boards here

KnowledgeLike-for-likePublic boards, shown as published, kept out of the index50

Knowledge benchmarks for Gemini 3.8 Flash and Grok 4.20
Benchmark	Gemini 3.8 Flash	Grok 4.20	Leader
MMLU Pro	90.2%	86.3%	Gemini 3.8 Flash
LegalBench (Vals AI)	87.0%	77.7%	Gemini 3.8 Flash
CaseLaw (Vals AI)	Not measured	54.4%	Only Grok 4.20 measured
CorpFin (Vals AI)	Not measured	63.7%	Only Grok 4.20 measured
TaxEval (Vals AI)	74.5%	74.1%	Gemini 3.8 Flash
MortgageTax (Vals AI)	65.3%	45.4%	Gemini 3.8 Flash
MedQA (Vals AI)	Not measured	94.5%	Only Grok 4.20 measured
MedCode (Vals AI)	48.1%	32.2%	Gemini 3.8 Flash
SimpleQA Verified	69.7%	Not measured	Only Gemini 3.8 Flash measured
LMArena Text: science	1523	Not measured	Only Gemini 3.8 Flash measured
LMArena Text: medicine and healthcare	1508	Not measured	Only Gemini 3.8 Flash measured
LMArena Text: legal and government	1497	Not measured	Only Gemini 3.8 Flash measured
LMArena Text: business and finance	1479	Not measured	Only Gemini 3.8 Flash measured
FACTS Benchmark Suite	69.4%	Not measured	Only Gemini 3.8 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 3.8 Flash and Grok 4.20
Benchmark	Gemini 3.8 Flash	Grok 4.20	Leader
Design Arena: websites	1300	1229	Gemini 3.8 Flash
Design Arena: UI components	1319	1199	Gemini 3.8 Flash
Design Arena: game dev	1305	1192	Gemini 3.8 Flash
Design Arena: data viz	1269	1217	Gemini 3.8 Flash
Design Arena: 3D	1295	1193	Gemini 3.8 Flash
Design Arena: all code categories	1304	1221	Gemini 3.8 Flash
Design Arena: SVG	1295	1164	Gemini 3.8 Flash
Design Arena: ASCII art	1265	1174	Gemini 3.8 Flash
LiveBench design	72.7%	Not measured	Only Gemini 3.8 Flash measured

GeneralLike-for-likePublic boards, shown as published, kept out of the index41

General benchmarks for Gemini 3.8 Flash and Grok 4.20
Benchmark	Gemini 3.8 Flash	Grok 4.20	Leader
Vals Index	56.0%	Not measured	Only Gemini 3.8 Flash measured
LiveBench data analysis	54.0%	Not measured	Only Gemini 3.8 Flash measured
Public Benefits Bench (Vals AI)	65.3%	Not measured	Only Gemini 3.8 Flash measured
SAGE (Vals AI)	35.1%	38.2%	Grok 4.20
MedScribe (Vals AI)	84.5%	63.4%	Gemini 3.8 Flash
Vals Multimodal Index	Not measured	39.1%	Only Grok 4.20 measured
IFBench	Not measured	81.2%	Only Grok 4.20 measured
Long context reasoning (AA-LCR)	84.0%	69.0%	Gemini 3.8 Flash
DTBench	95.7%	90.1%	Gemini 3.8 Flash
LMCA	52.9%	38.7%	Gemini 3.8 Flash
CL-bench	Not measured	22.2%	Only Grok 4.20 measured
Surface Evolver Bench	76.9%	Not measured	Only Gemini 3.8 Flash measured
Furniture assembly	31.7%	Not measured	Only Gemini 3.8 Flash measured
CL-bench Life	Not measured	11.9%	Only Grok 4.20 measured
LMArena Text	1499	Not measured	Only Gemini 3.8 Flash measured
LMArena Text: instruction following	1492	Not measured	Only Gemini 3.8 Flash measured
LMArena Text: creative writing	1488	Not measured	Only Gemini 3.8 Flash measured
LMArena Vision	1315	Not measured	Only Gemini 3.8 Flash measured
LMArena Text: English	1498	Not measured	Only Gemini 3.8 Flash measured
LMArena Text: non-English	1491	Not measured	Only Gemini 3.8 Flash measured
LMArena Text: Chinese	1553	Not measured	Only Gemini 3.8 Flash measured
LMArena Text: German	1501	Not measured	Only Gemini 3.8 Flash measured
LMArena Text: Japanese	1507	Not measured	Only Gemini 3.8 Flash measured
LMArena Text: Korean	1464	Not measured	Only Gemini 3.8 Flash measured
LMArena Text: French	1496	Not measured	Only Gemini 3.8 Flash measured
LMArena Text: Spanish	1487	Not measured	Only Gemini 3.8 Flash measured
LMArena Text: Russian	1514	Not measured	Only Gemini 3.8 Flash measured
LMArena Text: Polish	1497	Not measured	Only Gemini 3.8 Flash measured
LMArena Text: multi-turn	1503	Not measured	Only Gemini 3.8 Flash measured
LMArena Text: longer queries	1507	Not measured	Only Gemini 3.8 Flash measured
LMArena Text: writing and language	1494	Not measured	Only Gemini 3.8 Flash measured
LMArena Text: entertainment and media	1480	Not measured	Only Gemini 3.8 Flash measured
LMArena Vision: English	1318	Not measured	Only Gemini 3.8 Flash measured
LMArena Vision: Chinese	1416	Not measured	Only Gemini 3.8 Flash measured
LMArena Vision: reading text	1333	Not measured	Only Gemini 3.8 Flash measured
LMArena Vision: humor	1321	Not measured	Only Gemini 3.8 Flash measured
LMArena Vision: creative writing	1299	Not measured	Only Gemini 3.8 Flash measured
Neither model has a result on the other 9 boards here

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

Image generation benchmarks for Gemini 3.8 Flash and Grok 4.20
Benchmark	Gemini 3.8 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 3.8 Flash$0.0026Fits in one request

Grok 4.20$0.0025Fits in one request

Grok 4.20 costs less

Repository review

50K input + 3K output tokens

Gemini 3.8 Flash$0.049Fits in one request

Grok 4.20$0.070Fits in one request

Gemini 3.8 Flash costs less

Agent loop

200K input + 10K output tokens

Gemini 3.8 Flash$0.188Fits in one request

Grok 4.20$0.275Fits in one request

Gemini 3.8 Flash 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 3.8 Flash and Grok 4.20
Specification	Google Gemini 3.8 Flash	SpaceXAI Grok 4.20
Maker	Google	xAI
Weights	No public weights listed	No public weights listed
Released	September 2, 2026	March 31, 2026
Context window	1.05M	2M
Input $/Mtok	$0.75	$1.25
Output $/Mtok	$3.75	$2.50
Coding index	61.6	33.3
Independent measurements behind it	6	2
Cost per solved task	$2.74	$0.72
Source	OpenRouter listing	OpenRouter listing

Questions

Is Gemini 3.8 Flash better than Grok 4.20 for coding?

Pick Gemini 3.8 Flash for coding: it scores 61.6 on the Vibe Coding Index against 33.3 for Grok 4.20. Pick Grok 4.20 for output tokens 1.5x cheaper ($2.50 vs $3.75 per million) and a lower cost per solved task ($0.72 against $2.74).

Which is cheaper, Gemini 3.8 Flash or Grok 4.20?

Gemini 3.8 Flash costs $0.75 per million input tokens and $3.75 per million output tokens; Grok 4.20 costs $1.25 and $2.50. Per solved SWE-bench Verified task, Gemini 3.8 Flash costs $2.74 and Grok 4.20 $0.72.

Which has the bigger context window, Gemini 3.8 Flash or Grok 4.20?

Grok 4.20, with 2M tokens against 1.05M.

How many benchmarks is the Gemini 3.8 Flash vs Grok 4.20 comparison based on?

42 benchmarks have a result for both models as of October 21, 2026. Gemini 3.8 Flash's coding index rests on 6 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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Gemini 3.8 Flash or Grok 4.20: which to pick

Which one for your work

Coding

Intelligence

Agentic work

Reasoning

Math

Knowledge

Web design

General

Long documents

Everyday cost

Cost per solved task