IRC vs Slack: what got reinvented and what got lost

Slack's debt to IRC is right there in the interface: channels prefixed with #, /commands, @mentions, integrations posting into rooms. Early Slack even shipped an IRC gateway. The comparison is really a story about what polish costs.

What Slack added #

• Zero-setup persistence. History, search, file uploads and notifications work instantly for non-technical users — the single biggest thing plain IRC lacks out of the box.
• Workspace administration: SSO, compliance exports, user provisioning. This is why companies pay for it.
• Rich integrations with a polished (if rate-limited and ToS-bound) API.
• Threads, for better or worse.

What got lost #

• Openness. Slack is one vendor's closed service; the IRC gateway was shut down in 2018. Your client, your data and your message history exist at the vendor's pleasure, under the vendor's pricing — and the free tier's history limits have repeatedly tightened.
• Cross-organization community. A Slack workspace is a silo with invites. An IRC network is a commons: thousands of channels, one connection, no gatekeeper. "Community Slacks" reinvent this badly, one workspace and one account per community.
• Lightweight clients. Slack in a terminal, over SSH, on a decade-old machine? IRC does that natively.
• Automation without permission. An IRC bot needs no app review, no OAuth scopes and no admin approval — a socket and a loop suffice.

Different jobs #

In truth they rarely compete head-on anymore. Slack (and Teams) won internal company chat, where admin features matter and someone else pays. IRC remains strong where Slack is structurally wrong: open communities that no single organization owns, support channels anyone can join without an invite link, and infrastructure chat that must work when everything else is down.

If your open source project is choosing between a community Slack and an IRC channel: the Slack invite-link dance, history paywall and account requirement all add friction precisely for the drive-by contributors you want. The pragmatic modern stack is an IRC channel on Libera.Chat, with a bouncer or web client for the regulars — and Slack left for the office.