GPT-5 Nano
o200k_base
Structural tokenization analysis engine. Optimized for GPT-5 Nano inputs. Calibrate context windows and compute precise API economics in real-time.
Context
400k
Type
LLM
Encoding
o 200k base
CH44
WORD9
ENCODINGo200k_base
// HAPPYTOKENIZER: WAITING FOR INPUT STREAM
Quick Answers
What is the GPT-5 Nano token limit?
GPT-5 Nano supports a 400,000 token context window. Paste your text above to see how much of that window your prompt fills.
What tokenizer does GPT-5 Nano use?
GPT-5 Nano uses OpenAI's o200k_base encoding. This page counts tokens with the vendor's real vocabulary, so the numbers match what the API sees.
How much does GPT-5 Nano cost per million tokens?
GPT-5 Nano costs $0.05 per million input tokens and $0.40 per million output tokens, with cached input at $0.01 per million.
Model Insights
Modalities
InTextImage
OutText
Supported Features
StreamingStructured OutputsFunction CallingWeb SearchPrompt CachingReasoning Tokens
Supported Endpoints
ResponsesBatch
Cost Manifest
Input / 1M$0.05
Output / 1M$0.40
Cached Write$0.01
* Rates are estimated based on OpenAI standard tier. Actual billing may vary based on batch processing and enterprise agreements.
// Technical Specifications
- ARCHITECTURE ID
- gpt-5-nano
- TOKEN ENCODING
- o200k_base
- MAX CONTEXT
- 400,000TOKENS