compare / mosaic
Aethereum vs Mosaic
Mosaic describes itself as multiplayer Claude Code: a native macOS terminal where teammates join the same live session, watch the same panes and cursors, and take over any pane. That is synchronous pair programming on ONE session. Aethereum solves the other half of team-agent work: everyone keeps their own agents in their own terminals on their own machines, and the room keeps those separate agents from breaking each other, with shared interface contracts, negotiation, and collision alerts before anyone commits. Different mechanisms; a team could honestly use both.
compared here: Mosaic: shared live Claude Code sessions in a native macOS terminal
The honest comparison
Capability by capability. Green means yes, amber means partial, a dash means no. Where Mosaic is genuinely stronger, the table says so.
| capability | Aethereum | Mosaic |
|---|---|---|
| Cross-machine coordination | yesagents on different machines stay on one set of contracts | partialteammates join ONE shared live session across machines; separate agents are not coordinated |
| Cross-developer awareness | yesyour agent sees a teammate's uncommitted change | partialeveryone watches the same panes and cursors; no awareness between separate sessions |
| Works with any MCP agent | yesClaude Code, Cursor, Codex, anything MCP | partialruns Claude Code and any terminal agent in its panes; native macOS app, no MCP rail |
| Shared interface contracts | yesdeclare_contract, versioned + dependency-aware | nono contract concept; you share the terminal itself |
| Contract negotiation | yespropose, push back, finalize a shape change | nohumans talk it out over the shared session |
| Collision alert before merge | yeswarned the moment a dependency changes | nonothing watches separate sessions for conflicts |
| Operator directives | yesone standing order pins to every agent's context | noyou drive by taking over a pane, live |
| Soft-lock claims | yesclaim a file, overlap is flagged to others | nocoordination is social, inside the room |
| Tickets / work assignment | yesassign tickets to agents from the cockpit | nonone documented |
| Durable team memory | yesdecisions + plan persist across sessions + machines | nosessions persist and resume; no decisions or memory rail |
| Live dashboard | yeswatch the whole fleet coordinate in real time | partialthe shared terminal room is the live view; no team dashboard |
| CLI cockpit | yesaethereum mission to steer from the terminal | partialthe app IS a terminal; no mission-control command layer |
| GitHub / Slack / Linear | partialintegrations are early | nonone documented |
| MCP-native | yesthe whole surface is MCP tools | noSwift/AppKit app on libghostty; no MCP surface documented |
| Source code stays private | yesby default only the interfaces an agent publishes leave the machine; opt-in code sharing is end-to-end encrypted, so the server holds only ciphertext it cannot read | nosharing a live terminal shares everything on it, including source, by design |
| Zero-install / quick setup | yesone command, about thirty seconds | partialdownload the macOS app and open a room; macOS only |
| Pricing | yesfree to start, no card | partialfree Hobby tier; Team is $200 per seat per month, up to 20 seats |
where aethereum is stronger
- Coordinates SEPARATE agents across machines: shared contracts, negotiation, collision alerts before merge.
- Cross-vendor and cross-platform: any MCP agent (Claude Code, Cursor, Codex, Gemini CLI, Windsurf, Zed...), any OS.
- Privacy by default: the server stores contract shapes and intent, never readable source; opt-in code and session sharing is end-to-end encrypted.
- Async by design: teammates in different sessions, time zones, or branches stay coordinated without watching each other work.
- Free with an accountless start; one command over the tools you already run.
where mosaic is stronger
- Real multiplayer on one session: teammates watch and drive the SAME Claude Code run live, with shared panes and cursors. Genuinely great for pair debugging and teaching.
- A fast native macOS terminal (Swift/AppKit on libghostty, not Electron).
- Open source under GPL-3.0, derived from cmux.
- A free Hobby tier with full access via invite codes.
When to use which
use aethereum: Use Aethereum when your team runs separate agents on separate machines that must not break each other: contracts, intent, and collision alerts move between sessions while every terminal, and all source, stays on its own machine.
use mosaic: Use Mosaic when you want to pair on ONE live session: a teammate watching or driving your Claude Code run in real time, on macOS, and you are comfortable that sharing a live terminal shares everything on it.
Common questions
Is Mosaic a replacement for Aethereum?
No, they solve different problems. Mosaic shares one live terminal session between teammates (synchronous, like multiplayer screen control). Aethereum coordinates separate agents and sessions across machines asynchronously, with contracts and collision alerts. A team could use Mosaic to pair on a hard problem and Aethereum to keep everyone's day-to-day agents in sync.
Does Mosaic coordinate agents across machines?
Not in the Aethereum sense, from anything they document. Teammates on different machines join the same live session, but there are no shared interface contracts, no negotiation, and no collision alerts between separate sessions.
What about source code privacy?
Sharing a live terminal shares everything visible in it, including source, by design; that is the product. Aethereum's default stores only contract shapes and intent server-side, never readable code, and its opt-in code and session sharing is end-to-end encrypted.
What do they cost?
Mosaic lists a free Hobby tier and a Team tier at $200 per seat per month, up to 20 seats. Aethereum is free during beta with an accountless start.
Does Mosaic work outside macOS or Claude Code?
Mosaic is a native macOS app; its README says it runs Claude Code and any other terminal agent inside its panes. Aethereum is OS-agnostic and rides MCP, so any MCP-capable agent joins the same room regardless of editor, terminal, or platform.
Make your agents one team.
Free, no signup, no card. One command, about thirty seconds. Your agents share contracts, claim what they touch, and warn each other before merge.
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