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

> ## Agent Instructions
> To build and serve your own model, start at /deploy/development/quickstart and /deploy/development/overview. Model code imports reactor_runtime; Python client code imports reactor_sdk. The runtime overview explains the model interface. /deploy/development/local-testing pairs a complete brightness model with a Python client test in a separate brightness-test workspace, without weights, a GPU, or a browser. Rebuild after edits: reactor run reuses the existing image. Check deployment access and capacity before deploying.
> Reactor hosts multiple models, each with its own connect slug (modelName) and command/event schema. The catalog of every model — slug, typed SDK package, and links to its schema — is at /model-api-reference/overview. Some models expose one slug per experience (e.g. HappyOyster); always take the slug from the model's own pages, never guess it.
> Fastest path to a working app: `npx create-reactor-app my-app --model=<slug>` scaffolds a complete app with secure auth wired up. Typed TypeScript SDKs are published as @reactor-models/<model>; Python uses the base reactor-sdk package.
> Auth: exchange an API key (rk_...) for a JWT via POST https://api.reactor.inc/tokens from your server. Never put the API key in client-side code.
> Append .md to any docs URL for clean Markdown. Search these docs via the MCP server at https://docs.reactor.inc/mcp.

# Changelog

> Release notes for the Helios model API.

Changes to Helios's commands, messages, tracks, and defaults, newest first. SDK and platform
releases are in [Release Notes](/changelog/overview).

<Update label="July 31, 2026" description="Rewind">
  ### New

  * **Rewind.** Helios saves snapshots of the scene and returns to them on demand. [`save_snapshot`](/model-api-reference/helios/schema#save_snapshot) captures the world state, [`rewind`](/model-api-reference/helios/schema#rewind) restores it, and [`list_snapshots`](/model-api-reference/helios/schema#list_snapshots) reports what the buffer holds. The buffer keeps up to 50 snapshots per session and evicts the oldest once full; a `reset` empties it, and it is released when the session ends. Each snapshot records the one it descends from, so a save after a rewind branches off the restored snapshot while a save without one extends the branch in progress, and `current_snapshot_id` on the `state` message says which branch is live. Rewinding restores the scene but not the prompt, so send the prompt you want to continue with after the rewind. Available in `@reactor-models/helios` as `saveSnapshot`, `rewind`, and `listSnapshots`, with the matching `useHeliosSnapshotSaved`, `useHeliosRewindComplete`, `useHeliosRewindFailed`, and `useHeliosSnapshotList` hooks.
</Update>

<Update label="March 18, 2026" description="Image conditioning">
  ### New

  * **Image conditioning for Helios.** `set_image()` accepts a reference image to steer generation, with cut or blend transitions for swapping mid-stream. See [Helios](/model-api-reference/helios/overview).

  ### Improved

  * Image size guidance clarified: 64KB limit with JPEG quality 0.5 recommended for set-image calls.
</Update>

<Update label="March 10, 2026" description="Launch">
  ### New

  * **Helios launch.** Reactor's first interactive real-time video generation model, built on a 14B-parameter Diffusion Transformer. Produces a continuous infinite stream you can steer with prompts and reference images.
  * **Helios prompt guide.** A dedicated [Prompt Guide](/model-api-reference/helios/prompt-guide) covering scene composition, transitions, and steering techniques.
</Update>