Context Window

Compare

Claude Fable 5 Default vs GPT-5.1-Codex-Max

This page is context-first: how much text each model can take in one request. Full specs adds capabilities and limits; the pricing matrix below is only about $/million tokens from hosts that list both models.

Anthropic

Model

Claude Fable 5 Default

Image inputTool calling

Context window

1M

1,000,000 tokens · ~750K words

Model page
Openai

Model

GPT-5.1-Codex-Max

Image inputTool calling

Context window

400K

400,000 tokens · ~300K words

Model page

Context window · side by side

Bar length is relative to the larger of the two windows (100% = max of this pair). This is not pricing.

Claude Fable 5 Default1M
GPT-5.1-Codex-Max400K

Claude Fable 5 Default has about 2.5× the context window of the other in this pair.

Token calculator →Memory savings →

Claude Fable 5 Default has 150% more context capacity (1000K vs 400K tokens). GPT-5.1-Codex-Max is 87% cheaper on input.

Quick verdicts

Short takeaways — validate with your own workloads.

  • Long document processing

    Use Claude Fable 5 Default. Its 1000K context fits entire documents without chunking (vs 400K).

  • RAG / high-volume retrieval

    Use GPT-5.1-Codex-Max. Input tokens are 87% cheaper — critical when sending large retrieved contexts.

Full specs

Context, output, capabilities, and dates. Green highlights the favorable value where we compute a winner.

SpecClaude Fable 5 DefaultGPT-5.1-Codex-Max
Context window1,000,000 tokens (1000K)400,000 tokens (400K)
Max output tokens128,000 tokens (128K)128,000 tokens (128K)
Speed tierBalancedBalanced
VisionYesYes
Function callingYesYes
Extended thinkingYesYes
Prompt cachingYesYes
Batch APIYesNo
Release dateN/ADec 2025

Pricing matrix

Dollar rates only: hosts that list both models, per 1M tokens. For how much text fits, use the context section above — not this table.

ProviderClaude Fable 5 Default inClaude Fable 5 Default outGPT-5.1-Codex-Max inGPT-5.1-Codex-Max out
Google Vertex$10.00/M$50.00/M——
Openrouter——$1.25/M$10.00/M

Frequently asked questions

Claude Fable 5 Default has a larger context window: 1000K tokens vs 400K. For long documents, large codebases, or extended agent sessions, the larger context window reduces the need to chunk inputs or summarize history.

Powered by Mem0

Use a smaller model.
Get better results.

Mem0 gives your AI long-term memory so you stop re-sending context on every call. That means you can use a smaller, faster, cheaper model — and still get better answers.

Calculate your savingsLearn about Mem0

Example: a multi-turn chat session

Without Mem0~128K tokens sent
Full history
Repeated info
Old context
With Mem0~20K tokens sent
Key memories
Current turn

80% less to send — works with any model