Is Pi 1.0 free and open source?

Pi 1.0 is open source under the MIT license, with its code in the earendil-works/pi repository on GitHub. Earendil's announcement gives one-line installers for macOS and Linux (a curl script from pi.dev) and for Windows (a PowerShell script), and the docs live at pi.dev. The announcement does not list any paid plan for the harness itself.

What changed in Pi 1.0 compared with Pi 0.99?

Pi 0.99 added MCP and the codemode sandbox. Pi 1.0 makes the full-screen TUI the default, makes codemode leaner with about 40% fewer prompt tokens, adds image generation inside codemode, adds Radius sign-in to /login and a copy-code Anthropic login for headless setups, and hardens MCP OAuth with RFC 9207 iss validation and per-server credentials.

Pi Durable is an experimental framework Earendil released alongside Pi 1.0 for long-running agent applications. Pi Durable checkpoints every task, so an agent can resume after a crash, and it supports forked conversations, multiple clients steering one conversation, and memory, SQLite or JSONL storage. Earendil says its APIs may still change and that the source is about 15,000 lines.

Can I go back to the old Pi interface?

Pi 1.0 turns on the full-screen TUI by default, but the v1.0.0 release notes say users can switch back to the regular mode in settings. The release also adds a quieter header-only startup option that still shows the version and key hints, for people who prefer less output when Pi starts.

Earendil · 2026-10-01 · major

Pi 1.0 — Earendil's minimal coding agent reaches its first stable release

Pi 1.0 is the first stable release of Earendil's open-source, MIT-licensed agent harness. It makes the full-screen TUI the default, cuts codemode prompt tokens by about 40% and ships an experimental Pi Durable package.

Earendil announcement card for the Pi 1.0 release

Earendil calls Pi 1.0 a hardened, minimal, extensible agent harness that you can make your own.

Quick facts

Maker	Earendil
Version	v1.0.0
License	MIT
Codemode prompt	~5,300 → ~3,300 tokens (GPT-5.6)
Install (Windows)	powershell -c "irm https://pi.dev/install.ps1 \| iex"
Companion	Pi Durable (experimental, npm)

What is it?

Pi 1.0, released on 1 October 2026, is the first stable version of Earendil's terminal coding agent and agent toolkit. Earendil says hundreds of thousands of weekly users gave feedback over months of work toward it. The release builds on the MCP and codemode support that arrived in 0.99 and adds deferred tool loading, virtual model extensions and cache warming for Anthropic models.

How does it work?

Codemode lets the model write JavaScript that calls tools from a sandbox instead of one tool per turn; in v1.0.0 it is leaner, dropping a GPT-5.6 request from about 5,300 to about 3,300 prompt tokens, and it can generate images through models.generateImages(). Mid-conversation system messages let Pi change prompts and tools while staying aware of the transcript. On the security side, MCP OAuth now validates the RFC 9207 iss parameter and stores credentials per server.

Why does it matter?

A 1.0 tag signals that the harness is stable enough to build on, which matters because Pi is also used as a library by other agent projects. The companion Pi Durable package checkpoints every model call and tool call, so long-running agents can survive crashes and resume, and several clients can watch and steer the same conversation.

Who is it for?

developers who use or build coding agents

Frequently asked questions

Is Pi 1.0 free and open source?: Pi 1.0 is open source under the MIT license, with its code in the earendil-works/pi repository on GitHub. Earendil's announcement gives one-line installers for macOS and Linux (a curl script from pi.dev) and for Windows (a PowerShell script), and the docs live at pi.dev. The announcement does not list any paid plan for the harness itself.
What changed in Pi 1.0 compared with Pi 0.99?: Pi 0.99 added MCP and the codemode sandbox. Pi 1.0 makes the full-screen TUI the default, makes codemode leaner with about 40% fewer prompt tokens, adds image generation inside codemode, adds Radius sign-in to /login and a copy-code Anthropic login for headless setups, and hardens MCP OAuth with RFC 9207 iss validation and per-server credentials.
What is Pi Durable?: Pi Durable is an experimental framework Earendil released alongside Pi 1.0 for long-running agent applications. Pi Durable checkpoints every task, so an agent can resume after a crash, and it supports forked conversations, multiple clients steering one conversation, and memory, SQLite or JSONL storage. Earendil says its APIs may still change and that the source is about 15,000 lines.
Can I go back to the old Pi interface?: Pi 1.0 turns on the full-screen TUI by default, but the v1.0.0 release notes say users can switch back to the regular mode in settings. The release also adds a quieter header-only startup option that still shows the version and key hints, for people who prefer less output when Pi starts.

Try it

curl -fsSL https://pi.dev/install.sh | sh