Claude Fable 5.1 vs Gemini 3.1 Pro Preview Custom Tools vs GPT-6 Astra: side-by-side summary

Claude Fable 5.1, Gemini 3.1 Pro Preview Custom Tools, and GPT-6 Astra are available through the OpenRouter API, so switching between them takes a model slug change rather than a new integration.

Claude Fable 5.1, from Anthropic, has a 1,000,000-token context window and is priced at $10/M tokens input, $50/M tokens output on OpenRouter.

Gemini 3.1 Pro Preview Custom Tools, from Google, has a 1,048,576-token context window and is priced at $2/M tokens input, $12/M tokens output on OpenRouter.

GPT-6 Astra, from OpenAI, has a 1,050,000-token context window and is priced at $10/M tokens input, $50/M tokens output on OpenRouter.

Context window

• Claude Fable 5.1: 1,000,000 tokens
• Gemini 3.1 Pro Preview Custom Tools: 1,048,576 tokens
• GPT-6 Astra: 1,050,000 tokens

Price

• Claude Fable 5.1: $10/M tokens input, $50/M tokens output
• Gemini 3.1 Pro Preview Custom Tools: $2/M tokens input, $12/M tokens output
• GPT-6 Astra: $10/M tokens input, $50/M tokens output

Provided by

• Claude Fable 5.1: Anthropic
• Gemini 3.1 Pro Preview Custom Tools: Google
• GPT-6 Astra: OpenAI