> ## Documentation Index
> Fetch the complete documentation index at: https://docs.usesynth.ai/llms.txt
> Use this file to discover all available pages before exploring further.

# Connect Synth

> Sign in to unlock hosted SMR, Factories, hosted optimizers, and Synth inference from Stack.

<Note>
  Documents the Stack **`0.2.0-dev.20260702.3`** hosted-connect surface. Synth
  sign-in is optional; local Stack continues to work without it.
</Note>

Connect Stack when you want cloud-backed Synth features. The same environment
selector in the cockpit can target dev, staging, or prod, and each environment
uses its configured API base URL and auth variable.

## Get a key

Create a key at [usesynth.ai/keys](https://usesynth.ai/keys), then export it in
your shell or configure an `authEnvFile`.

```bash theme={null}
export SYNTH_API_KEY="sk_..."
stack doctor
```

For staging, use the environment variable configured in your `stack.config.json`
for staging, usually `SYNTH_STAGING_API_KEY`.

## Auth commands

```bash theme={null}
stack auth urls --json
stack auth open signup
stack auth open signin
stack auth open keys
stack auth verify --json
```

The browser URLs carry Stack attribution for product activation. They do not
paste credentials into Stack prompts or logs.

## What unlocks

| Feature           | What changes after connect                                                           |
| ----------------- | ------------------------------------------------------------------------------------ |
| Hosted SMR        | List runs, inspect questions/approvals, message runs, preview outputs                |
| Factories         | List Factories, inspect linked projects/runs, wake or pause/resume with confirmation |
| Hosted optimizers | List jobs, preview/download artifacts, cancel jobs                                   |
| Remote sync       | Record push/pull receipts and remote gardener narration                              |
| Synth inference   | Read catalog/usage and use opt-in aux or billed GLM profiles                         |

If auth is missing or rejected, hosted surfaces show a point-of-need connect
prompt. Local work remains available.

## Keep keys out of prompts

Use environment variables or `authEnvFile`; do not paste raw keys into prompts,
tickets, screenshots, or logs.

Next: [Hosted ops](/stack/hosted-ops) and [Hosted inference](/stack/inference).