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What is the AI cost per token? Definition and business implications
Cost per token is the elementary economic unit of an AI deployment. Providers bill input tokens (your prompt) and output tokens (the model's response) separately, with a typical ratio of 1 to 5. Mastering this cost requires distinguishing unit prices, consumed volumes, and optimisation levers.
Cost per token is expressed in dollars per million tokens (MTok). Anthropic prices as of October 2026 illustrate the orders of magnitude. Claude Haiku 5.5 (lightweight model, released on 7 October 2026): $0.10 input, $0.50 output per MTok for prompts up to 100,000 tokens, $0.50 / $2.50 beyond. Claude Sonnet 5.5 (quality/cost balance): $2 / $10. Claude Opus 5.5 (advanced model): $4 / $20. Claude Fable 5.1 (flagship model): $10 / $50. The output/input ratio is 5:1 across the whole Anthropic line-up. OpenAI applies the same ratio: GPT-6.1 Sol at $2 / $10, GPT-6 Astra at $10 / $50, with a higher rate for very long requests. DeepSeek V4.1 Flash goes down to $0.30 input and $1.20 output at peak hours, half price off-peak. Three optimisation levers exist. Batch API: minus 50% on input and output, for non-interactive uses. Prompt caching: context read back from the cache costs 10% of the normal input price, or even less on the most recent models (repeated contexts, system prompts). Adapted model choice: a Haiku 5.5 costs forty times less than an Opus 5.5, and a hundred times less than a Fable 5.1 (prompts up to 100,000 tokens), for classification, extraction, or routing use cases.
Concrete example
A 90-employee SME uses an AI assistant via the Claude Sonnet 5.5 API for 3,000 requests per day. A typical exchange consumes 800 input tokens and 400 output tokens. Monthly calculation at September 2026 prices: 3,000 × 22 days × 800 input × ($2/MTok) = $106 for input. 3,000 × 22 × 400 × ($10/MTok) = $264 for output. Gross total: $370 per month, or about $4,400 per year. Activating prompt caching on the 600 tokens of common context: those tokens are read back at 5% of the price on Sonnet 5.5, the input bill drops by more than two thirds, an annual saving of about $900 (excluding cache write costs, marginal at this volume). Switching to Haiku 5.5, twenty times cheaper than Sonnet 5.5, for 40% of simple requests (request classification): about $1,350 additional annual saving.
FAQ
How is cost per token billed?
In dollars per million tokens (MTok), and above all by distinguishing input (your prompt) from output (the model's response), billed separately. The typical ratio is 1 to 5: at Anthropic as at OpenAI, an output token costs five times an input token.
Is comparing providers on unit price alone reliable?
No, it is misleading. The displayed price is only an indicator: the actual cost depends on the effective token volume, the model chosen and the use of optimisation levers. A head-to-head comparison on unit price alone leads you astray.
Which levers reduce the bill?
Mainly three. The Batch API, which takes 50% off input and output for non-interactive uses. Prompt caching, where context read back from the cache costs 10% of the normal input price, or even less. And choosing an adapted model: a Haiku 5.5 costs forty times less than an Opus 5.5 for classification, extraction or routing tasks.
Why do long responses cost more than long prompts?
Because of the 5-to-1 ratio between output and input. Long prompts are cheap; long generations are five times more expensive. Outputs therefore weigh more in the bill than inputs.
How do we choose the right model on cost?
The golden rule: Haiku for simple tasks, Sonnet for standard uses, Opus only for critical cases. Per token, Haiku 5.5 costs forty times less than Opus 5.5 (prompts up to 100,000 tokens): keep the most expensive models for the tasks that need them.
See also
Further reading
Sources
- Anthropic documentation, Pricing: Claude rates, Batch API and prompt caching, October 2026. https://platform.claude.com/docs/en/about-claude/pricing
- OpenAI API Pricing: GPT-6 Astra, GPT-6.1 Sol, GPT-6 Luna, September 2026. https://developers.openai.com/api/docs/pricing
- DeepSeek API Docs, Models & Pricing: DeepSeek V4.1 Flash and V4 Pro, September 2026. https://api-docs.deepseek.com/quick_start/pricing