Overview
Gemini 4 Argon is Google's flagship reasoning model, generally available since October 13, 2026 through the Gemini API, AI Studio and the Gemini app. Claude Fable 5.1, released September 1, 2026, is the current version of Anthropic's Fable line and the model Anthropic recommends for its most demanding reasoning and long-horizon agentic work.
What the vendors publish
Gemini 4 Argon (model ID gemini-4-argon): text, image, video, audio and PDF input with text output; a unified 1,048,576-token context window; 65,536 output tokens by default and up to 1,048,576 with long decode; thinking levels low, medium (default) and high.Argon pricing: $2 per 1M input tokens and $10 per 1M output tokens at an introductory rate through November 30, 2026, rising to $4 and $20 from December 1. Implicit caching discounts cached input by 95%. Argon is not on the Gemini API free tier.Claude Fable 5.1 (model ID claude-fable-5-1): text and image input with text output, a 1M-token context window, 128K max output, adaptive thinking that is always on, default effort high, and a June 2026 reliable knowledge cutoff.Fable 5.1 pricing: $10 per 1M input tokens and $50 per 1M output tokens, with cache reads at $0.25 per 1M. Anthropic lists its comparative latency as slower than the rest of the current Claude lineup.Benchmarks
Google says Argon ranks first on the Vals Index, which covers finance, coding, legal and tax work. Anthropic does not publish a matching figure for Fable 5.1 on that index, and neither vendor publishes a shared head-to-head benchmark, so we do not rank one above the other.
How to choose
Choose Argon if you need native video, audio or PDF input, very long outputs through long decode, or lower per-token cost during the introductory period.Choose Fable 5.1 if your workload is already built on Claude tooling and you need Anthropic's strongest generally available model for long-running agentic work, and the higher token price is acceptable.No hands-on testing was conducted for this comparison. Every figure above comes from the official pages listed under Research sources, as published on or before October 22, 2026. Where a vendor has not published a number, we say so instead of estimating it.