OpenAITokenCounter

OpenAITokenCounter uses OpenAI's POST /v1/responses/input_tokens endpoint to count the input tokens for a specific model. It supports text, images, files, tool calls, tool results, and tool schemas in the same format used by the Responses API.

Because it calls a remote API, it requires an OpenAI API key and adds network latency. Use it when you need model-specific counts or need to measure non-text inputs and tool schemas accurately. For local estimates, use ApproximateTokenCounter or TiktokenCounter.

python

from haystack.dataclasses import ChatMessage
from haystack.token_counters import OpenAITokenCounter

counter = OpenAITokenCounter("gpt-5-mini")
messages = [ChatMessage.from_user("What's Natural Language Processing?")]

token_count = counter.count(messages)

By default, the counter reads the API key from OPENAI_API_KEY. You can also pass a Haystack Secret explicitly and configure the API base URL, organization, timeout, retry count, and HTTP client options.

See the Token Counters API reference for all constructor parameters and methods.