Aion 3.5 and Aion 3.5 Mini

What Aion 3.5 is

Aion 3.5 and Aion 3.5 Mini are large language models for roleplay and storytelling, released on 23 September 2026 by AionLabs, a company that sells AI models through its own API and through OpenRouter. Both are built on the GLM family of models from the Chinese lab Z.ai, and both are sold as aion-labs/aion-3.5 and aion-labs/aion-3.5-mini.

AionLabs’ model list describes both the same way: “A multi-model system built on the GLM family of models. Aion 3.5 employs a collaborative generation process in which multiple specialized models contribute to each response.” The company says the result is “stronger narrative structure, more compelling tension and conflict, and a nuanced treatment of mature and darker themes.”

AionLabs, at aionlabs.ai, sells what its site calls “Intelligence On Demand”: an OpenAI-compatible API for “creative writing, roleplay, research, and production” work. It is a separate business from AION Labs, the Israeli drug-discovery venture studio at aionlabs.com.

What they cost

Aion 3.5 costs $3 per million input tokens and $6 per million output tokens, and Aion 3.5 Mini costs $0.70 and $1.40. The figures are the same on AionLabs’ own model list and on OpenRouter’s catalogue, read on 23 September 2026.

Both models carry the prices of the Aion 3.0 generation they follow: Aion 3.0 at $3 and $6, and Aion 3.0 Mini at $0.70 and $1.40.

Specifications

Aion 3.5 and Aion 3.5 Mini share one specification: a 262,144-token context window, which AionLabs lists as 256K, up to 32,768 tokens of output, and text in and text out. The figures come from OpenRouter’s model catalogue and AionLabs’ model list.

Reasoning cannot be switched off. OpenRouter’s catalogue marks it as mandatory for both models, with three effort levels and high as the default.

The Aion models before 3.5

Aion 3.5 is AionLabs’ fifth generation of writing models, and the first to move both its sizes onto GLM. Each earlier Aion model was a version of an open model from another lab, tuned for fiction.

All the release dates are AionLabs’ own. The 3.5 generation doubles the context window of Aion 3.0 at the same price.

Only the first model, Aion-RP 1.0, has public weights: it is on Hugging Face under the Apache 2.0 licence, where AionLabs describes it as “trained to excel at roleplaying and creative writing”. Aion 2.0, 3.0 and 3.5 are sold through the API only.

Who it is for

Aion 3.5 is built for interactive fiction: character roleplay, long-running stories and writing that deals with dark or adult themes. The 256K context gives a long story room to keep its earlier chapters in view, and the Mini version brings the price to under a quarter of the full model’s.

AionLabs’ launch material is its model list and the two OpenRouter entries, so the way to judge the models is to try them. Both are live on OpenRouter, where a single API key reaches them alongside other creative-writing models.

For the model family Aion 3.5 is built on, see GLM-5.3 and GLM-5.3 Flash.