September Release Surge Across Major AI Labs

The first half of September 2026 saw an unprecedented wave of model releases from the world’s leading AI companies, with Anthropic, OpenAI, Meta, Google, DeepSeek, and Sakana AI all announcing new versions.

Anthropic’s Claude Fable 5.1 and Claude Mythos 5.1

Anthropic released Claude Fable 5.1 on September 1, 2026, alongside Claude Mythos 5.1, described as the trusted-access twin of Fable 5.1.

Claude Fable 5.1 launched at the same price as Claude Fable 5: $10 per 1M input tokens and $50 per 1M output tokens. However, cache reads are priced at $0.25 per 1M tokens, lower than its predecessor.

Performance improvements are notable: Claude Fable 5.1 achieved a self-reported Terminal-Bench-Science score of 52.6, compared to 24.7 for Claude Fable 5.

OpenAI’s GPT-6 Astra and Image Models

OpenAI released GPT-6 Astra on September 3, 2026. The model is priced at $10 per 1M input tokens, $1 per 1M cached tokens, $12.50 per 1M cache-write tokens, and $50 per 1M output tokens. GPT-6 Astra has a context window of 1.05 million tokens and supports 128K output tokens.

Two days earlier, on September 8, 2026, OpenAI released GPT Image 2.5 Flare and GPT Image 2.5 Sunburst.

Meta, Google, and DeepSeek Announcements

Meta released Muse Spark 1.3 and Muse Spark 1.3 Contributor on September 2, 2026. Google released Gemini 3.8 Flash on the same date.

DeepSeek released DeepSeek V4.1 Flash on September 10, 2026.

Sakana AI’s Latest Releases

Sakana AI released Fugu Ultra v2.0 and Fugu Max on September 11, 2026.

Anthropic IPO Plans

In related news, Anthropic has selected the Nasdaq for its potential IPO.

Microsoft’s Code of Conduct for MAI Models

Microsoft CEO Satya Nadella announced a Code of Conduct for Microsoft’s MAI models on September 14, 2026.

Source: LLM Gateway