As of August 20, 2026, Grok 4.5 is 29% cheaper per million tokens than GPT-5.1 Thinking. GPT-5.1 Thinking is $1.25 / $10.00 per million input/output tokens versus Grok 4.5 at $2.00 / $6.00. Sources: https://developers.openai.com/api/docs/pricing and https://docs.x.ai/docs/models
Sources: OpenAI API pricing (https://developers.openai.com/api/docs/pricing); xAI API pricing (https://docs.x.ai/docs/models)
GPT-5.1 Thinking
OpenAI
Input
$1.25
Output
$10.00
Grok 4.5
xAI
Input
$2.00
Output
$6.00
Token pricing, specs, and benchmarks side by side
GPT-5.1 ThinkingGrok 4.5Verdict
Grok 4.5 offers both lower pricing and stronger benchmark performance across the board, making it the clear value leader in this comparison.
As of August 20, 2026, Grok 4.5 is 29% cheaper on blended LLM API pricing. Grok 4.5 costs $2.00 per million input tokens and $6.00 per million output tokens ($8.00 blended 1M-in + 1M-out). GPT-5.1 Thinking costs $1.25 / $10.00 per million tokens ($11.25 blended). Sources: https://developers.openai.com/api/docs/pricing and https://docs.x.ai/docs/models. The cheapest LLM for your app still depends on how many output tokens you generate.
GPT-5.1 Thinking OpenAI API pricing is $1.25 input and $10.00 output per million tokens via OpenAI. Grok 4.5 xAI API pricing is $2.00 input and $6.00 output per million tokens via xAI. Use those four numbers, not ChatGPT Plus or Claude Pro subscription prices, when you are comparing APIs.
Grok 4.5 leads on SWE-bench Verified: GPT-5.1 Thinking at 76.3% vs Grok 4.5 at 86.6%. SWE-bench measures real GitHub fixes; LiveCodeBench measures contest programming.
GPT-5.1 Thinking supports a 400K token context window, while Grok 4.5 supports 500K tokens. Grok 4.5 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.
Grok 4.5 leads on 3 of 4 shared benchmarks versus GPT-5.1 Thinking's 1 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 GPT-5.1 Thinking and Grok 4.5 are production API models. For cost-sensitive production traffic, Grok 4.5 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 GPT-5.1 Thinking through OpenAI and Grok 4.5 through xAI 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 OpenAI API pricing and xAI API pricing, quoted per million tokens. Official rate sheets: https://developers.openai.com/api/docs/pricing and https://docs.x.ai/docs/models. 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.
GPT-5.1 Thinking supports up to 128K output tokens per request, while Grok 4.5 supports up to an unspecified number of output tokens. Output tokens are usually the expensive half of API pricing, so a higher max output cap is a capability, not a discount.
GPT-5.1 Thinking runs at approximately 80 tokens/second while Grok 4.5 runs at 80 tokens/second. Grok 4.5 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.
Use the model pickers at the top of this LLM comparison. Search any model in the index and the URL updates. Open GPT-5.1 Thinking or Grok 4.5 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. GPT-5.1 Thinking costs $1.25/M input and $10.00/M output. Grok 4.5 costs $2.00/M input and $6.00/M output.
Rank both on the LLM leaderboard, SWE-bench, and Humanity's Last Exam.
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