Question 1

What does this Step 3.5 Flash vs Grok 4.20 (Reasoning) comparison cover?

Accepted Answer

It brings together documented inputs and outputs, token limits, deployment terms and available pricing. When both models have source-linked, verified results on a shared benchmark, those results are shown with their individual sources. The comparison is a starting point for evaluating your own workload.

Question 2

Which is cheaper: Step 3.5 Flash or Grok 4.20 (Reasoning)?

Accepted Answer

Step 3.5 Flash lists $0.10 input and $0.30 output per 1M tokens. Grok 4.20 (Reasoning) lists $1.25 input and $2.50 output. The cheaper workload depends on the mix of input and output. Long-context tiers, caching, batch processing and retries can change the bill.

Question 3

Which has the larger context window: Step 3.5 Flash or Grok 4.20 (Reasoning)?

Accepted Answer

Step 3.5 Flash lists 256K tokens and Grok 4.20 (Reasoning) lists 1M. Grok 4.20 (Reasoning) therefore has the larger recorded context window, but capacity alone is not a quality score.

Question 4

Which is faster: Step 3.5 Flash or Grok 4.20 (Reasoning)?

Accepted Answer

There is no matched speed measurement for both models with the same source, host, region and date. Test the same prompts at your expected concurrency and measure time to the first useful response as well as complete task time.

Question 5

What input and output types do Step 3.5 Flash and Grok 4.20 (Reasoning) support?

Accepted Answer

Step 3.5 Flash records text input and text output. Grok 4.20 (Reasoning) records text, image, pdf input and text output. “Not documented” means the current source record is incomplete; it does not prove that a modality is unsupported.

Question 6

Should I choose Step 3.5 Flash or Grok 4.20 (Reasoning)?

Accepted Answer

Consider Step 3.5 Flash if you need larger maximum output or a lower listed input rate or a lower listed output rate. Consider Grok 4.20 (Reasoning) if you need larger context. Step 3.5 Flash offers downloadable weights; Grok 4.20 (Reasoning) is listed as a proprietary model. Compare licence terms and operating costs before choosing a deployment. Test both on the same representative examples and judge the output against your acceptance criteria. Include tool failures, retries and the time to a completed task.

Specification	Step 3.5 Flash	Grok 4.20 (Reasoning)
Provider	StepFun	xAI
Listed pricing route	StepFun	xAI
Model family	—	grok
Accepted inputs	text	text, image, pdf
Produced outputs	text	text
Context window	256K	1MHigher
Max output	256KHigher	30K
Input price / 1M	$0.10Lower	$1.25
Output price / 1M	$0.30Lower	$2.50
Reasoning mode	Documented	Documented
Tool calling	Documented	Documented
Image input	Not documented	Documented
Audio input	Not documented	Not documented
Structured output	Not documented	Documented
License	Open weights	Proprietary

Step 3.5 Flash vs Grok 4.20 (Reasoning)

Step 3.5 Flash

Grok 4.20 (Reasoning)

Key differences

Pricing, limits and capabilities

Which model should you choose?

Documentation and model profiles

Questions people ask

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