Which is cheaper, Grok-4 Fast Reasoning or Step-3.5-Flash?
As of August 25, 2026, Step-3.5-Flash is 29% cheaper on blended LLM API pricing. Step-3.5-Flash costs $0.10 per million input tokens and $0.40 per million output tokens ($0.50 blended 1M-in + 1M-out). Grok-4 Fast Reasoning costs $0.20 / $0.50 per million tokens ($0.70 blended). Sources: https://docs.x.ai/docs/models and https://anotherwrapper.com/tools/llm-pricing. The cheapest LLM for your app still depends on how many output tokens you generate.
How much does Grok-4 Fast Reasoning vs Step-3.5-Flash cost per million tokens?
Grok-4 Fast Reasoning xAI API pricing is $0.20 input and $0.50 output per million tokens via xAI. Step-3.5-Flash StepFun API pricing is $0.10 input and $0.40 output per million tokens via StepFun. Use those four numbers, not ChatGPT Plus or Claude Pro subscription prices, when you are comparing APIs.
Which is better for coding, Grok-4 Fast Reasoning or Step-3.5-Flash?
Step-3.5-Flash leads on SWE-bench Verified: Grok-4 Fast Reasoning at 45.4% vs Step-3.5-Flash at 74.4%. SWE-bench measures real GitHub fixes; LiveCodeBench measures contest programming.
What is the context window for Grok-4 Fast Reasoning vs Step-3.5-Flash?
Grok-4 Fast Reasoning supports a 2M token context window, while Step-3.5-Flash supports 66K tokens. Grok-4 Fast Reasoning offers a larger context window. Filling a larger window bills more input tokens, so the cheaper-per-million model can still cost more on long documents.
Which model performs better on benchmarks, Grok-4 Fast Reasoning or Step-3.5-Flash?
Step-3.5-Flash leads on 3 of 3 shared benchmarks versus Grok-4 Fast Reasoning's 0 wins. Check the comparison table for GPQA Diamond, SWE-bench, MMLU, HLE, and the other evals we track. Token price and benchmark score together are the usual LLM comparison, not either number alone.
Is Grok-4 Fast Reasoning or Step-3.5-Flash better for production use?
Both Grok-4 Fast Reasoning and Step-3.5-Flash are production API models. For cost-sensitive production traffic, Step-3.5-Flash has better economics on the blended 1M-in + 1M-out scale. For maximum capability, weight the benchmark table for your domain. Many production stacks route cheap models for drafts and a frontier model for the hard turn, which is usually cheaper than sending everything to the expensive API.
Can I switch between Grok-4 Fast Reasoning and Step-3.5-Flash in my app?
Yes. Call Grok-4 Fast Reasoning through xAI and Step-3.5-Flash through StepFun with separate API keys, or through a gateway that already wraps both. Keep prompts in tokens, not characters, when you estimate the invoice. AnotherWrapper templates can swap providers without rewriting auth and billing.
How accurate is this Grok-4 Fast Reasoning vs Step-3.5-Flash pricing data?
List rates are the latest published xAI API pricing and StepFun API pricing, quoted per million tokens. Official rate sheets: https://docs.x.ai/docs/models and https://anotherwrapper.com/tools/llm-pricing. Prompt caching, batch APIs, and committed-use discounts can change the invoice. Benchmark scores are from official publications and independent evals, updated as new numbers land.
What is the output token limit for Grok-4 Fast Reasoning and Step-3.5-Flash?
Grok-4 Fast Reasoning supports up to 30K output tokens per request, while Step-3.5-Flash supports up to 8K output tokens. Output tokens are usually the expensive half of API pricing, so a higher max output cap is a capability, not a discount.
Which model has better throughput, Grok-4 Fast Reasoning or Step-3.5-Flash?
Grok-4 Fast Reasoning runs at approximately 90 tokens/second while Step-3.5-Flash runs at 150 tokens/second. Step-3.5-Flash is faster in raw throughput. Throughput (tokens per second) and time-to-first-token are why two models with the same per-million-token price can still feel different in chat and agents.
How do I switch the models in this Grok-4 Fast Reasoning vs Step-3.5-Flash comparison?
Use the model pickers at the top of this LLM comparison. Search any model in the index and the URL updates. Open Grok-4 Fast Reasoning or Step-3.5-Flash from the sidebar for the single-model API pricing page, or go back to the LLM pricing table to sort by cheapest blended cost.
