Question 1

What does this Fugu Ultra vs Step 3.5 Flash 2603 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: Fugu Ultra or Step 3.5 Flash 2603?

Accepted Answer

Fugu Ultra lists $5.00 input and $30.00 output per 1M tokens. Step 3.5 Flash 2603 lists $0.10 input and $0.30 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: Fugu Ultra or Step 3.5 Flash 2603?

Accepted Answer

Fugu Ultra lists 1M tokens and Step 3.5 Flash 2603 lists 256K. Fugu Ultra therefore has the larger recorded context window, but capacity alone is not a quality score.

Question 4

Which is faster: Fugu Ultra or Step 3.5 Flash 2603?

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 Fugu Ultra and Step 3.5 Flash 2603 support?

Accepted Answer

Fugu Ultra records text, image input and text output. Step 3.5 Flash 2603 records text 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 Fugu Ultra or Step 3.5 Flash 2603?

Accepted Answer

Consider Fugu Ultra if you need larger context. Consider Step 3.5 Flash 2603 if you need a lower listed input rate or a lower listed output rate. Step 3.5 Flash 2603 offers downloadable weights; Fugu Ultra 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	Fugu Ultra	Step 3.5 Flash 2603
Provider	Sakana AI	StepFun
Listed pricing route	Sakana AI	StepFun
Model family	fugu	—
Accepted inputs	text, image	text
Produced outputs	text	text
Context window	1MHigher	256K
Max output	—	256K
Input price / 1M	$5.00	$0.10Lower
Output price / 1M	$30.00	$0.30Lower
Reasoning mode	Documented	Documented
Tool calling	Documented	Documented
Image input	Documented	Not documented
Audio input	Not documented	Not documented
Structured output	Documented	Not documented
License	Proprietary	Open weights

Fugu Ultra vs Step 3.5 Flash 2603

Fugu Ultra

Step 3.5 Flash 2603

Key differences

Pricing, limits and capabilities

Which model should you choose?

Documentation and model profiles

Questions people ask

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