AI & LLM
Token, cost & context tools for LLMs
Claude Context Window Checker — Does Your Prompt Fit Claude Opus 4.8?
Claude Opus 4.8 has a 1,000,000-token (1M) context window as of 2026-07-03. The context window covers all tokens in one API turn: system prompt + messages + model response. The max output (128,000 tokens) is a separate, smaller limit — the model cannot generate more than 128,000 tokens in a single response even if the context window has room. With 32,000 tokens reserved for output, the usable input space is 968,000 tokens. An 800,000-token prompt fits within that input space. Paste your prompt to check fit before calling the Anthropic API.
Claude Opus 4.8 context window: 1,000,000 tokens
- Claude Opus 4.8 max output: 128,000 tokens (separate limit)
- Usable input (1,000,000 − 32,000 reserved output): 968,000 tokens
- Example check: 800,000-token prompt → FITS
- Data as of 2026-07-03
Frequently asked questions
What is the context window of Claude Opus 4.8?
Claude Opus 4.8 has a 1,000,000-token (1M) context window. At 0.75 words per token, that is roughly 750,000 words — equivalent to 2–3 full-length novels or a large codebase. The maximum output per response is 128,000 tokens. Note: token counts for Claude are estimated (Anthropic's tokenizer is proprietary); add 10–15% headroom for safety on large prompts. Data as of 2026-07-03.
What is the difference between Claude's context window and max output?
Claude Opus 4.8's context window (1,000,000 tokens) is the total budget for an API call — input + output combined. The max output (128,000 tokens) caps how long a single response can be. If you send 872,000 tokens of input, you have exactly 128,000 tokens of output budget remaining. Exceeding either limit produces an API error.