What kinds of examples are included?

The playground tutorial covers basics up through demos like filtering Hacker News for posts not about AI, joining a chatroom that only lets 'posh' messages through, monitoring a GitHub discussion and filing an issue when it becomes actionable, and classifying how your day is going.

Cryo is made by Endothermic Labs; the playground tutorial is signed by Zach Wade and Endothermic Labs.

The playground links to a GitHub repository, but the site doesn't state a license or make an explicit open-source claim.

How much does Cryo cost?

No pricing information is given on the site; the playground itself is free to use in the browser.

Cryolang — Run, freeze, and thaw programs in your browser

Cryo is a new programming language from Endothermic Labs, designed for long-running tasks like agents and workflows. Programs run on the Freeze/Thaw Virtual Machine (FTVM), which can freeze a running program, kill the process, and thaw it later so it picks up exactly where it left off — keeping a program going for an indefinite period of time. The cryolang playground runs a small version of the language directly in your browser, complete with an interactive tutorial and example plugins.

Key Features

Freeze/Thaw Virtual Machine (FTVM)

Run a program, freeze it, kill the process, and thaw it later — the program resumes as if nothing happened, built to keep long-running tasks (agents, workflows) alive indefinitely.

In-browser playground

A small version of Cryo runs entirely in your browser, with Run / Freeze / Thaw / Reset controls and a guided tutorial (with a built-in example editor and 'Try it out' buttons for each demo).

Example plugins

Programs can import capabilities from plugins such as 'hn' (Hacker News stories), 'github' (authenticate, users, discussions, comments, issues), 'rooms' (chatrooms), 'llm' (completion), and 'jev'.

Jev: typed LLM classification

The 'jev' plugin classifies text into types you declare, so the answer can only be one of the type's members and match statements are compile-checked for every case. It also provides 'noul', a probability (in thousandths) that a proposition is true.

Coroutines and select

The language includes coroutines and a select statement for waiting on multiple sources (e.g., room messages and stdio) at once, plus pipes for streaming values between tasks.

Modern type system

Cryo supports unions, generics, and higher-kinded types, as showcased in the playground's example list.

Durable chat / event replay semantics

A frozen-and-thawed bot in a chatroom 'hears everything it missed, in order' — the runtime handles what happened while the process was dead.

How It Works

Write and run Cryo code in the browser

The playground provides an editor with examples (Hacker News filtering, chatroom bots, GitHub discussion monitoring, mood classification, and more) that you can run with a single click.

Freeze and thaw to survive process death

While a program is waiting (e.g., asking for input or listening to a room), you can freeze it, kill the process, and thaw it — the program resumes and picks up everything it missed.

Compose with plugins

Programs import functionality from plugins ('hn', 'github', 'rooms', 'llm', 'jev') and coordinate results through pipes, selects, and coroutines.

Pros & Cons

Pros

Novel freeze/thaw execution model purpose-built for long-lived agents and workflows that outlive processes
Typed LLM classification (Jev) catches missing match cases and invalid classifications at compile time
Runs directly in the browser with zero setup and a step-by-step tutorial
Concrete, working example plugins (Hacker News, GitHub, chatrooms, LLM) rather than toy demos
Modern language features including unions, generics, and higher-kinded types

Cons

Who It's For

Best for

Developers curious about a persistence-first language for agents and long-running workflows
Engineers building bots or automation that must survive restarts and pick up missed events in order
People experimenting with LLM integration that is checked by the type system rather than free-form strings

Not ideal for

Teams that need a mature language with an established ecosystem, libraries, and long-term support
Workloads requiring floating-point math or fine-grained numeric precision
Anyone unwilling to experiment with an early-stage language and runtime

Use Cases

Building fleets of tiny agents that need to survive restarts and run indefinitely

Long-running workflows that wait on external events (chat messages, HN posts, GitHub discussions) and resume after freeze/thaw

LLM-assisted classification and decision making with compile-checked result types (via Jev)

Bots that monitor Hacker News and filter posts by topic using LLM judgment

Interactive GitHub automation, e.g., starting a discussion and filing an issue once a thread becomes actionable

FAQ

What is Cryo?

Cryo is a new programming language from Endothermic Labs for building fleets of tiny agents. It's designed for long-running tasks like agents and workflows and runs on the Freeze/Thaw Virtual Machine (FTVM), which is built to keep a program going for an indefinite period of time.

How does freeze/thaw work?

You run a program, freeze it, kill the process, and later thaw it — the program resumes where it left off. For example, a chatroom bot that is frozen while the room talks will 'hear everything it missed, in order' when thawed.

Do I need to install anything to try it?

No. The playground runs a small version of Cryo right in your browser, with Run, Freeze, Thaw, and Reset controls and a guided tutorial. Some examples ask you to sign in with GitHub or use Cloudflare to prevent abuse.

How does Cryo handle LLM output?

Cryolang