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

# Environment variables

# Environment Variables

Atomic accepts environment variables for configuration, provider credentials, and subprocess context. Atomic-prefixed application variables take precedence over their legacy Pi aliases when both are set.

## Application configuration

| Atomic variable                   | Legacy alias                  | Purpose                                                                  |
| --------------------------------- | ----------------------------- | ------------------------------------------------------------------------ |
| `ATOMIC_CODING_AGENT_DIR`         | `PI_CODING_AGENT_DIR`         | Agent/config directory; default `~/.atomic/agent`                        |
| `ATOMIC_CODING_AGENT_SESSION_DIR` | `PI_CODING_AGENT_SESSION_DIR` | Session directory; `--session-dir` takes precedence                      |
| `ATOMIC_PACKAGE_DIR`              | `PI_PACKAGE_DIR`              | Package directory override                                               |
| `ATOMIC_OFFLINE`                  | `PI_OFFLINE`                  | Disable startup network operations                                       |
| `ATOMIC_SKIP_VERSION_CHECK`       | `PI_SKIP_VERSION_CHECK`       | Skip automatic startup version checks; explicit self-update still checks |
| `ATOMIC_TELEMETRY`                | `PI_TELEMETRY`                | Enable/disable install/update telemetry                                  |
| `ATOMIC_REDUCED_MOTION`           | `PI_REDUCED_MOTION`           | Use static reduced-motion presentation                                   |

`PI_CACHE_RETENTION=long` is a provider/upstream prompt-cache option and intentionally has no Atomic-prefixed alias. `VISUAL` and `EDITOR` select the Ctrl+G external editor when `externalEditor` is unset.

## Provider credentials

Provider keys include `ANTHROPIC_API_KEY`, `OPENAI_API_KEY`, `AZURE_OPENAI_API_KEY`, `GEMINI_API_KEY`, AWS/Bedrock credentials, and the variables listed in [Providers](/providers#environment-variables-or-auth-file). `ANTHROPIC_AUTH_TOKEN` is a distinct header-only bearer credential for Anthropic-compatible gateways: Atomic sends `Authorization: Bearer …` without requiring or inventing an API key, including normal turns, isolated execution, branch summaries, and Verbatim Compaction. Custom headers remain independent.

## Bash session environment

Every built-in, factory-created, direct, foreground/background, workflow-stage, and isolated bash execution receives one execution-time snapshot:

| Atomic variable          | Exact Pi alias       | Value                                                     |
| ------------------------ | -------------------- | --------------------------------------------------------- |
| `ATOMIC_SESSION_ID`      | `PI_SESSION_ID`      | Active session ID                                         |
| `ATOMIC_SESSION_FILE`    | `PI_SESSION_FILE`    | Active JSONL file; omitted for unsaved/ephemeral sessions |
| `ATOMIC_PROVIDER`        | `PI_PROVIDER`        | Active provider; omitted when no model is selected        |
| `ATOMIC_MODEL`           | `PI_MODEL`           | Active model ID; omitted when no model is selected        |
| `ATOMIC_REASONING_LEVEL` | `PI_REASONING_LEVEL` | Active reasoning level                                    |

Atomic clears these ten reserved names before overlaying the current snapshot, preventing stale metadata from another session or workflow stage. Unrelated inherited/caller variables remain intact. The snapshot is taken when execution begins, so a resumed session or later model change is reflected. SDK `createBashTool()` exposes it by default; set `exposeSessionEnvironment: false` to opt out.

See [Using Atomic](/usage#environment-variables) and [RPC direct bash](/rpc#bash) for execution and streaming behavior.