Which is cheaper, GPT-5.1 Instant or GPT-5.5 Pro?
As of August 20, 2026, GPT-5.1 Instant is 98% cheaper on blended LLM API pricing. GPT-5.1 Instant costs $1.25 per million input tokens and $10.00 per million output tokens ($11.25 blended 1M-in + 1M-out). GPT-5.5 Pro costs $60.00 / $480.00 per million tokens ($540.00 blended). Sources: https://developers.openai.com/api/docs/pricing and https://developers.openai.com/api/docs/pricing. The cheapest LLM for your app still depends on how many output tokens you generate.
How much does GPT-5.1 Instant vs GPT-5.5 Pro cost per million tokens?
GPT-5.1 Instant OpenAI API pricing is $1.25 input and $10.00 output per million tokens via OpenAI. GPT-5.5 Pro OpenAI API pricing is $60.00 input and $480.00 output per million tokens via OpenAI. Use those four numbers, not ChatGPT Plus or Claude Pro subscription prices, when you are comparing APIs.
Which is better for coding, GPT-5.1 Instant or GPT-5.5 Pro?
GPT-5.1 Instant has a published SWE-bench Verified score of 76.3%. GPT-5.5 Pro does not have that eval on this page yet.
What is the context window for GPT-5.1 Instant vs GPT-5.5 Pro?
GPT-5.1 Instant supports a 400K token context window, while GPT-5.5 Pro supports 1M tokens. GPT-5.5 Pro 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, GPT-5.1 Instant or GPT-5.5 Pro?
GPT-5.5 Pro leads on 2 of 2 shared benchmarks versus GPT-5.1 Instant'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 GPT-5.1 Instant or GPT-5.5 Pro better for production use?
Both GPT-5.1 Instant and GPT-5.5 Pro are production API models. For cost-sensitive production traffic, GPT-5.1 Instant 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 GPT-5.1 Instant and GPT-5.5 Pro in my app?
Yes. Call GPT-5.1 Instant through OpenAI and GPT-5.5 Pro through OpenAI 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 GPT-5.1 Instant vs GPT-5.5 Pro pricing data?
List rates are the latest published OpenAI API pricing and OpenAI API pricing, quoted per million tokens. Official rate sheets: https://developers.openai.com/api/docs/pricing and https://developers.openai.com/api/docs/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 GPT-5.1 Instant and GPT-5.5 Pro?
GPT-5.1 Instant supports up to 128K output tokens per request, while GPT-5.5 Pro supports up to 128K 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, GPT-5.1 Instant or GPT-5.5 Pro?
GPT-5.1 Instant has a measured throughput of approximately 100 tokens/second. Throughput data for GPT-5.5 Pro 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.
How do I switch the models in this GPT-5.1 Instant vs GPT-5.5 Pro comparison?
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 Instant or GPT-5.5 Pro from the sidebar for the single-model API pricing page, or go back to the LLM pricing table to sort by cheapest blended cost.
