As of August 20, 2026, Grok 4 Fast is 81% cheaper per million tokens than Kimi K2.5. Grok 4 Fast is $0.20 / $0.50 per million input/output tokens versus Kimi K2.5 at $0.59 / $3.09. Sources: https://docs.x.ai/docs/models and https://platform.kimi.com/docs/pricing/chat
Sources: xAI API pricing (https://docs.x.ai/docs/models); Moonshot AI pricing (https://platform.kimi.com/docs/pricing/chat)
Grok 4 Fast
xAI
Input
$0.20
Output
$0.50
Kimi K2.5
Moonshot AI
Input
$0.59
Output
$3.09
Token pricing, specs, and benchmarks side by side
Grok 4 FastKimi K2.5Verdict
Grok 4 Fast offers significantly lower pricing, while Kimi K2.5 leads on benchmark performance. Your choice depends on whether cost efficiency or raw capability matters more for your use case.
As of August 20, 2026, Grok 4 Fast is 81% cheaper on blended LLM API pricing. Grok 4 Fast costs $0.20 per million input tokens and $0.50 per million output tokens ($0.70 blended 1M-in + 1M-out). Kimi K2.5 costs $0.59 / $3.09 per million tokens ($3.68 blended). Sources: https://docs.x.ai/docs/models and https://platform.kimi.com/docs/pricing/chat. The cheapest LLM for your app still depends on how many output tokens you generate.
Grok 4 Fast xAI API pricing is $0.20 input and $0.50 output per million tokens via xAI. Kimi K2.5 Moonshot AI API pricing is $0.59 input and $3.09 output per million tokens via Moonshot AI. Use those four numbers, not ChatGPT Plus or Claude Pro subscription prices, when you are comparing APIs.
Kimi K2.5 has a published SWE-bench Verified score of 76.8%. Grok 4 Fast does not have that eval on this page yet.
Grok 4 Fast supports a 2M token context window, while Kimi K2.5 supports 262K tokens. Grok 4 Fast 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.
Kimi K2.5 leads on 9 of 9 shared benchmarks versus Grok 4 Fast'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.
Both Grok 4 Fast and Kimi K2.5 are production API models. For cost-sensitive production traffic, Grok 4 Fast 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.
Yes. Call Grok 4 Fast through xAI and Kimi K2.5 through Moonshot AI 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.
List rates are the latest published xAI API pricing and Moonshot AI API pricing, quoted per million tokens. Official rate sheets: https://docs.x.ai/docs/models and https://platform.kimi.com/docs/pricing/chat. 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.
Grok 4 Fast supports up to 30K output tokens per request, while Kimi K2.5 supports up to 262K output tokens. Output tokens are usually the expensive half of API pricing, so a higher max output cap is a capability, not a discount.
Grok 4 Fast has a measured throughput of approximately 90 tokens/second. Throughput data for Kimi K2.5 is not yet available. 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.
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 or Kimi K2.5 from the sidebar for the single-model API pricing page, or go back to the LLM pricing table to sort by cheapest blended cost.
This comparison covers API pricing, context window, throughput, and benchmark scores. Grok 4 Fast costs $0.20/M input and $0.50/M output. Kimi K2.5 costs $0.59/M input and $3.09/M output.
Rank both on the LLM leaderboard, SWE-bench, and Humanity's Last Exam.
The index
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