Tinker: a training API for researchers and developers - Tinker Documentation

Tinker: a training API for researchers and developers

Tinker lets you focus on what matters in LLM post-training — your data and algorithms — while we handle the heavy lifting of distributed training.

You write a simple loop that runs on your CPU-only machine, including the data or environment and the loss function. We figure out how to make the training work on a bunch of GPUs, doing the exact computation you specified, efficiently. To change the model you're working with, you only need to change a single string in your code.

Tinker gives you full control over the training loop and all the algorithmic details. It's not a magic black box that makes fine-tuning "easy". It's a clean abstraction that shields you from the complexity of distributed training while preserving your control.

Here's how the division of responsibilities works in practice:

You focus on	You write	We handle
Datasets and RL environments Your custom training data	Simple Python script Runs on your CPU	Efficient distributed training of large models Qwen3.5-397B, Kimi K2.6
Training logic Your loss functions, training loop, and evals	API calls `forward_backward()` `optim_step()` `sample()` `save_state()`	Reliability Hardware failures handled transparently

Features

What the Tinker service currently supports:

Tinker lets you fine-tune open-weight models ranging from 1B to 1T+ parameters, including both dense and mixture-of-experts architectures. See Models & Pricing for the full list.
Tinker supports vision-language models (VLMs) like Qwen3.6-35B-A3B for image understanding tasks. See the Rendering tutorial for details.
Tinker implements low-rank adaptation (LoRA) fine-tuning, not full fine-tuning. However, we believe that LoRA gives the same performance as full fine-tuning for many important use cases, especially in RL (see LoRA Without Regret).
You can download the weights of your trained model to use outside of Tinker, for example with your inference provider of choice.

A quick look at functionality

Tinker's main functionality is contained in a few key functions:

forward_backward: feed in your data and loss function, and we'll compute and accumulate the gradients for you.
optim_step: update your model using the accumulated gradients
sample: Generate outputs from your trained model
other functions for saving and loading weights and optimizer state