Gemini 3.8 Flash vs Grok 4.5: price, scores, context

Side-by-side comparison

Criterion	Gemini 3.8 Flash	Grok 4.5
Developer	Google DeepMind	xAI
Released	September 2, 2026	July 8, 2026
Capability index	83.7 / 100	79.1 / 100
Input price	$0.75	$2
Output price	$3.75	$6
Cost of a typical task	$0.023	$0.052
Context window	1,048,576 tokens	500,000 tokens
Maximum output	65,536 tokens	500,000 tokens
Reasoning mode	Yes	Yes
Tool calling	Yes	Yes
Accepted inputs	text, image, video, audio, PDF	text, image, PDF
Open weights	No	No
Knowledge cutoff	Not disclosed	Not disclosed

The match-up at a glance

This comparison pits two mid-range models, balancing quality and cost against each other: Gemini 3.8 Flash and Grok 4.5, one from Google DeepMind, the other from xAI. The first dates from September 2, 2026, the second from July 8, 2026.

All figures below come from public sources checked on October 22, 2026: models.dev and OpenRouter for prices and capabilities, Epoch AI for scores.

What the benchmarks say

On our capability index, Gemini 3.8 Flash scores 83.7 out of 100 and Grok 4.5 79.1. Gemini 3.8 Flash leads by 4.6 points.

On the 5 benchmarks reported for both, Gemini 3.8 Flash wins 4 times and Grok 4.5 1:

GPQA Diamond (PhD-level science questions): Gemini 3.8 Flash 95.4%, Grok 4.5 93.4%
OTIS Mock AIME (competition mathematics problems): Gemini 3.8 Flash 98.9%, Grok 4.5 97.8%
FrontierMath (very hard research-level mathematics): Gemini 3.8 Flash 68.4%, Grok 4.5 57.2%
FrontierCode (advanced programming tasks): Gemini 3.8 Flash 41.2%, Grok 4.5 42.4%
APEX-Agents (professional tasks carried out by an agent): Gemini 3.8 Flash 64.3%, Grok 4.5 56.2%

Budget

Gemini 3.8 Flash costs $0.75 per million input tokens and $3.75 per million output tokens; Grok 4.5 costs $2 and $6.

For a typical agent task (read 20,000 tokens, write 2,000), expect $0.023 with Gemini 3.8 Flash versus $0.052 with Grok 4.5. Gemini 3.8 Flash is 2.3 times cheaper, a gap that adds up quickly over 1,000 tasks: $29.5 difference.

Run the numbers with your own volumes in the agent cost calculator.

Features and limits

Gemini 3.8 Flash reads more in one go: 1,048,576 tokens of context (roughly 1,573 pages), versus 500,000 for Grok 4.5.

Reasoning mode: Gemini 3.8 Flash yes, Grok 4.5 yes. Tool calling: Gemini 3.8 Flash yes, Grok 4.5 yes. Image input: Gemini 3.8 Flash yes, Grok 4.5 yes.

Neither publishes its weights: both are used through an API.

In short

Our reading of the data:

Choose Gemini 3.8 Flash for a higher capability index, a lower cost, a larger context window and a more recent release.

This verdict relies on public figures; it does not replace a trial on your own tasks.

Frequently asked questions

Gemini 3.8 Flash or Grok 4.5: which is better?

On our index (Epoch AI data), Gemini 3.8 Flash scores 83.7 and Grok 4.5 79.1 out of 100. The best choice also depends on price and on your use case.

Which one is cheaper?

Gemini 3.8 Flash. To read 20,000 tokens and write 2,000, expect $0.023 with Gemini 3.8 Flash and $0.052 with Grok 4.5 (prices as of October 22, 2026).

Which one has the larger context window?

Gemini 3.8 Flash, with 1,048,576 tokens versus 500,000.

Can I run Gemini 3.8 Flash or Grok 4.5 on my own servers?

No: both are closed models, available through an API.

Gemini 3.8 Flash or Grok 4.5: which to choose?