asciinema CLI 3.0 Release Announcement Published on 15 Sep 2025 by Marcin Kulik --- Overview asciinema CLI 3.0 is a complete rewrite in Rust. It upgrades the recording file format, introduces terminal live streaming, and brings many improvements. The rewrite in Rust improves startup speed, installation ease (static binary), and enables new features by integrating the Rust-based asciinema virtual terminal. For full details, see the release notes and changelog. --- asciicast v3 File Format Evolution of asciicast v2 format to fix prior shortcomings. Uses intervals (deltas) for timing session events instead of absolute timestamps. Makes editing recordings easier without adjusting all timestamps. Header is reorganized; terminal metadata grouped under term. New event type: "x" to store session exit status. Allows line comments with #. Example format snippet shows clear event streams with timing deltas. Supported by both asciinema server and player. --- Live Terminal Streaming Two streaming modes introduced: Local mode: Uses built-in HTTP server for streaming on trusted networks (LAN). No data leaves the machine except to browser clients. CLI bundles latest asciinema player for viewing. Remote mode: Streams via asciinema server (asciinema.org or self-hosted) to shareable URLs. Modes can be used simultaneously. Example live stream demo running btop provided. Streaming architecture and protocols details: docs. asciinema player adapts buffering dynamically for smooth viewing. asciinema server can record live streams into regular recordings. Currently, asciinema.org disables stream recording and limits 1 concurrent stream. Self-hosted servers have no such limits by default. Thanks to Brightbox for cloud services supporting asciinema.org. --- Local-First Approach Changes Historical behavior: asciinema rec uploaded by default unless saving locally was specified. Problems addressed: Misconception that uploading to asciinema.org is mandatory. Security risk of accidentally uploading sensitive terminal data. To improve safety and clarity: In 3.0, filename argument is required. asciinema rec no longer uploads recordings automatically. For uploads, users must explicitly use asciinema upload <filename>. Encourages users to save locally or self-host their servers. Aims to reduce accidental data leaks and misconceptions about data sharing. --- More Self-Hosting Friendly New server URL prompt enables users to specify/ascii an asciinema server when using commands like upload, stream, or auth. Defaults to https://asciinema.org for convenience but is fully user selectable and saved for future use. Eases use in interactive and containerized environments. Provides an extra safeguard against unintended uploads to asciinema.org. --- Summary asciinema CLI 3.0 is a significant update centered on Rust rewrite, new file format, live streaming, and better user control over data sharing. The release is available now but may take time to appear in package repos. Prebuilt binaries for Linux/macOS available on the GitHub release page. Source code and build instructions also available. The author welcomes feedback and can be contacted via Mastodon @ku1ik@hachyderm.io. --- Links of Importance: Getting Started Explore Recordings Forum [Live