Together AI Launches Together Post-Training Service for Custom Models

Together AI on October 19, 2026, launched Together Post-Training, a service for building custom models through user-defined reinforcement learning and supervised fine-tuning loops, with introductory pricing of $9 per GPU-hour of B200 usage for the first six weeks. The service is designed for building custom models both from environment rewards via RL and from supervision data via SFT.

Customers define the training loop, including data, environments, and agentic harnesses, and can add steps such as logging or external benchmarking, while Together co-optimizes the underlying systems and infrastructure for model quality and training speed. Together said it built the service because RL infrastructure is growing more complex and many companies that could benefit from post-training never start, or start and stall, under the infrastructure burden.

The service launches with open-weight models Muse Spark Open, GLM 5.3, Kimi K3, and Qwen 3.8-27B, and Together said it will expand the selection in the coming weeks to cover both frontier LLMs and efficient smaller models. For the first six weeks, the service is offered at a reduced price of $9 per GPU-hour of B200…