An AI model's context window is the maximum amount of text - measured in tokens - it can read and reason over in a single request. This tool compares context windows across 19 leading LLMs from OpenAI, Anthropic, Google, Meta, Mistral, and more so you can pick the right model for long-document tasks.
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How it works
Use the calculator below to convert your documents to tokens. As a rough rule, 1 token equals about 4 characters of English text, or three-quarters of a word.
Sort the table by context window size or filter by vendor to see which models can fit your full input with headroom for the response.
Larger context windows usually cost more per request and can hurt accuracy. Pick the smallest model that comfortably fits your task, then test with real prompts.
Comparison chart
Showing 19 of 19 models
| Model | Vendor | Context Window | Released | Words | Output cap | Notes |
|---|---|---|---|---|---|---|
| Gemini 1.5 Pro | 2M tokens | 2024 | ~1.5M words | 8,192 out | Largest publicly available context window. | |
| GPT-4.1 | OpenAI | 1M tokens | 2025 | ~750K words | 32,768 out | Long-context variant for big-document workflows. |
| Gemini 1.5 Flash | 1M tokens | 2024 | ~750K words | 8,192 out | Fast, efficient long-context model. | |
| Gemini 2.0 Flash | 1M tokens | 2024 | ~750K words | 8,192 out | Improved Flash with native tool use and multimodal output. | |
| Grok 3 | xAI | 1M tokens | 2025 | ~750K words | Not published | Long-context successor with stronger reasoning. |
| Codestral | Mistral | 256K tokens | 2024 | ~192K words | Not published | Specialized code model, larger context for repos. |
| o1 | OpenAI | 200K tokens | 2024 | ~150K words | 100,000 out | Reasoning model, extended chain-of-thought. |
| o3-mini | OpenAI | 200K tokens | 2025 | ~150K words | 100,000 out | Cost-efficient reasoning model. |
| Claude Opus 4.7 | Anthropic | 200K tokens 1M tokens beta | 2026 | ~150K words | 32,000 out | Frontier model. 1M-token beta context for select customers. |
| Claude Sonnet 4.6 | Anthropic | 200K tokens 1M tokens beta | 2025 | ~150K words | 32,000 out | Balanced performance and price. 1M beta context available. |
| Claude Haiku 4.5 | Anthropic | 200K tokens | 2025 | ~150K words | 8,192 out | Fast, low-cost tier with full 200K context. |
| Grok 2 | xAI | 131K tokens | 2024 | ~98K words | Not published | Available via X Premium and the xAI API. |
| GPT-4o | OpenAI | 128K tokens | 2024 | ~96K words | 16,384 out | Multimodal flagship: text, image, audio input. |
| GPT-4 Turbo | OpenAI | 128K tokens | 2023 | ~96K words | 4,096 out | Predecessor to GPT-4o, still widely available. |
| Llama 3.1 405B | Meta | 128K tokens | 2024 | ~96K words | Not published | Open-weights flagship. Self-hosting possible. |
| Llama 3.3 70B | Meta | 128K tokens | 2024 | ~96K words | Not published | Smaller, faster open-weights model. Cheaper to host. |
| Mistral Large 2 | Mistral | 128K tokens | 2024 | ~96K words | Not published | European frontier model with strong multilingual support. |
| Command R+ | Cohere | 128K tokens | 2024 | ~96K words | Not published | RAG-optimized with native citations and tool use. |
| DeepSeek V3 | DeepSeek | 128K tokens | 2024 | ~96K words | Not published | Open-weights MoE model, strong reasoning at low cost. |
Approximations: 1 token ≈ 4 characters of English text ≈ 0.75 words. One printed page ≈ 500 tokens. Vendor caps and beta tiers change frequently - always confirm in the official API docs before deploying.
Token calculator
Paste any text below to get an instant token estimate (using the standard ~4 characters per token heuristic) and see which models can fit it inside their context window.
Type or paste text to see which models have a large enough context window.
FAQ
An AI model's context window is the maximum amount of text - measured in tokens - that the model can read and reason over in a single request. It includes your prompt, any attached documents, prior conversation, and the model's own output. Once the limit is reached, older content is dropped or the request fails.
Google's Gemini 1.5 Pro currently leads with a 2 million token context window, the largest publicly available. Gemini 1.5 Flash, Gemini 2.0 Flash, GPT-4.1, and Grok 3 each offer 1 million tokens. Claude Opus 4.7 and Sonnet 4.6 ship with 200K standard but have a 1 million token beta tier for enterprise customers.
Roughly 400 pages of English text, or about 150,000 words. As a rule of thumb, 1 token is about 0.75 words and one page of standard prose is around 500 tokens. A 200K context can fit a 600-page novel, a long technical RFC, or a few hours of meeting transcripts.
Not always. Larger windows let you pass more material in a single call, but most models suffer from a 'lost in the middle' effect where information buried deep in the prompt is recalled less reliably. For best results, place the most important context near the top or bottom, and use retrieval augmented generation rather than dumping entire corpora.
The total context window is shared between input (your prompt plus attached files) and output (the model's response). For example, GPT-4o has 128K total context but caps output at 16K tokens, and Claude Opus 4.7 caps output at 32K. If you need long generated responses, check the output limit separately - it is usually much smaller than the input limit.
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