Slack does not feed your messages to a chatbot, but it does train models on them by default, and for some communities that is reason enough to leave. Here are six alternatives that take the question off the table.
You moderate a 6,000-member community that runs on Slack, a mix of open-source contributors, a few paid maintainers, and a lot of people who joined to ask questions and vent. One Monday a new AI panel appears in the sidebar, offering to summarize channels you never asked it to read. Nobody on your team switched it on with any real intent, and now half the members are asking who else can see those summaries.
That reaction is the whole problem. Slack is not hiding any of this, and its policy is public. The friction is that a default changed under a community that never signed up to be part of an AI feature, and the people running it get almost no granular control over what happens next. If your group handles anything sensitive, from security disclosures to health peer support, or the kind of labor organizing that gets people fired, “trust us” is a thin answer. This guide covers what Slack actually does with your messages, then the alternatives that let a community stop worrying about it.
The Short Version
Slack says it does not train chatbots or large language models on your messages, and that part is true. What it does do is use your workspace’s content to train its own non-generative models, things like search ranking and channel suggestions, and that happens by default unless an admin emails Slack to opt the whole workspace out. Its paid Slack AI add-on also reads message content to build summaries and answers. If your community wants none of that, the reliable fix is to stop handing the data to a vendor at all. Self-hosted, open-source chat does exactly that: Mattermost is the closest thing to a drop-in Slack, Zulip suits busy asynchronous communities, Rocket.Chat scales without a user cap, Element adds end-to-end encryption, and Campfire is a one-time purchase you own outright. Hosted-but-private options exist too, but self-hosting is the version with no asterisks.
Table of Contents
What Slack actually does with your messages
Start with the distinction Slack itself draws, because most “Slack is training AI on you” posts blur it. Slack’s privacy principles say plainly that the company does “not develop generative AI models using Customer Data,” and that it will not use your content to train generative models “unless Customer provides affirmative opt-in consent.” Slack AI, the paid feature that writes summaries, runs on off-the-shelf models that, in Slack’s words, “are not updated by and don’t in other ways retain Customer Data after a request.” The fear that your channel is being poured into the next public chatbot is not the thing that is happening.
Now the part that is real. Slack does use customer data to train its own non-generative machine learning, the models behind search results, channel recommendations, and emoji suggestions. That training runs by default. To stop it, a workspace owner has to email feedback@slack.com with the subject line “Slack Global model opt-out request,” which is not a setting any ordinary member can find and flip.
Two things about that opt-out are worth noticing on your own. It is an all-or-nothing, org-wide email, so you cannot exclude one sensitive channel while leaving the rest in. And it only governs the global training models, doing nothing about Slack AI reading content once someone on the team turns the add-on on. For a small private team, that may be perfectly fine. For a community of thousands who never agreed to any of it, the controls are too coarse to promise anyone real privacy.
| Slack behavior | What it means for a private community |
|---|---|
| Trains chatbots or LLMs on your messages | No, not without affirmative opt-in |
| Trains its own search and recommendation models on your content | Yes, by default; opt out by email |
| Slack AI reads messages to write summaries and answers | Yes, when the paid add-on is enabled |
| Per-channel or per-member privacy control | No; the levers are workspace-wide |
Why self-hosting settles the question
Every opt-out, retention setting, and privacy policy is a promise from a company that also has a commercial reason to use your data. Self-hosting takes the promise out of the equation. When the server sits on infrastructure you control, no vendor holds your plaintext, there is nothing to summarize on a whim, and no model is being trained on the far side of an API. The question of what Slack is doing with your messages stops having an answer, because there is no Slack in the picture. Communities uneasy about software quietly reading their content are part of a wider shift, and it shows up outside chat too, in the same instinct we covered in our look at Google Photos alternatives that skip face grouping.
That control comes with a bill, and it is worth saying out loud. You take on updates, backups, storage, and the security work Slack otherwise does for you. A community with no technical volunteer will feel that weight quickly. The tools below fall into two groups for exactly that reason: ones a small team can stand up on a $6 virtual server in an afternoon, and ones that expect steady operations attention.
Six Slack alternatives that keep AI out of the room
All six are open source or source-available, and none of them trains anything on your conversations, because the conversations never leave your servers. Where they differ is in shape and in how much operational effort they ask of you.
Mattermost — closest to a Slack you can move into
Mattermost maps almost one-to-one onto Slack: channels, threads, webhooks, slash commands, the same muscle memory your members already have. The free Team Edition is open source under an MIT license, carries no message-history cap, and runs up to 250 users as a single Linux binary with PostgreSQL behind it. Watch one 2025 change here. The newer “Entry” free tier limits visible history to 10,000 messages across the whole server, so a community that wants an uncapped archive should deploy Team Edition on purpose rather than accept whatever the installer defaults to. Mattermost’s own editions documentation spells out which free build is which.
Zulip — built for communities that never stop talking
Zulip’s real difference is topic threading. Every message lives under a named topic inside a channel, so a 4,000-person community reads like a forum you can actually catch up on instead of a wall you scroll and give up on. It is fully open source, free to self-host with every feature included, and run by the nonprofit Zulip Foundation as of 2026. If you would rather not host it yourself, Zulip Cloud gives open-source projects and similar communities its paid Standard plan at no cost; otherwise the free cloud tier keeps 10,000 messages of history and Standard runs $8 per user per month. For a distributed group spread across time zones, the threading does more for daily sanity than any single privacy setting.
Rocket.Chat — no user ceiling when you self-host
Rocket.Chat’s Community Edition is the option that refuses to put a number on your membership: unlimited users, unlimited history, self-hosted, with an MIT-licensed core. It ships more than most communities will touch, including voice, video, and omnichannel inboxes, which reads as either generous or heavy depending on your appetite for a bigger install. Once your community is past a few hundred people and still growing, the absence of a seat cap matters more than a slick setup wizard.
Element — when private has to mean encrypted
Element runs on the Matrix protocol with end-to-end encryption on by default, so even the server operator cannot read the messages. That is a firmer guarantee than “we promise not to look,” and it is why the French government (through its Tchap system), the German Bundeswehr, and NATO run on Matrix rather than a commercial chat app, as Element documents. The cost is real: federation plus encryption make Element the most involved of these to deploy and maintain, and self-hosters have historically hit “unable to decrypt” errors across devices, though longtime users report that has largely settled down. Choose Element when encryption is the requirement rather than a nice-to-have.
Campfire — pay once, own the code, no AI
Campfire, from the team behind Basecamp, is the outlier. It is a one-time $299 purchase with no subscription, and you get all the source code to run on your own server for unlimited users. It is deliberately small, with rooms, direct messages, search, and file sharing, and nothing resembling an AI assistant anywhere in it. For a community that wants boring, permanent, and fully owned, the Campfire model is the least fussy answer on this list.
If your community looks more like Discord or a forum
Real-time team chat is not the only shape a community takes. If yours feels like Discord, Stoat (the open-source project formerly called Revolt) is self-hostable and familiar to that crowd. If it is really a slow-moving discussion board, a forum tool such as Discourse fits better than any chat app while keeping the same “your server, your data” property. Match the tool to how people actually talk, not to the product you happen to be replacing.
How the six compare
| Platform | Best for | Hosting | AI on your data | Cost to start |
|---|---|---|---|---|
| Mattermost | Slack-style teams up to 250 | Self-hosted (Team Edition) | None | Free, open source |
| Zulip | Busy asynchronous communities | Self-host or free cloud for OSS | None | Free self-host; $8/user cloud |
| Rocket.Chat | Large, growing memberships | Self-hosted | None | Free, unlimited users |
| Element | Encryption-first groups | Self-host (Matrix) | None; end-to-end encrypted | Free, open source |
| Campfire | Own-it-forever simplicity | Self-hosted | None | $299 one-time |
| Discourse / Stoat | Forums or Discord-style groups | Self-hosted | None | Free, open source |
The questions to ask before you switch
Leaving Slack over privacy and then landing on a tool with the same problems is an easy mistake to make. Before you commit a community to any platform, get concrete answers to these. They also work as a script for testing a hosted option that claims to be private.
- Is AI processing off by default, or do you have to hunt for a setting to disable it? A tool that ships an AI summarizer switched on has already told you its priorities.
- Can you turn AI features off per channel, or only for the whole workspace? Coarse controls are how members get surprised.
- Where does the data physically live, and can you export all of it in an open format if you leave? “Your data” is only true when you can walk out with it.
- If it is hosted, is the training opt-out a checkbox or a support-ticket email? The harder it is to find, the more the default matters.
- Is message history genuinely uncapped, or does the free tier bury everything past 10,000 messages? Communities live and die on their archive.
- Who is legally responsible for the server, and are you ready for backups and updates? For self-hosting, this is the question people skip and later regret.
How to choose
For most communities leaving Slack over AI, start with Mattermost. It is the smallest jump for your members, it holds up to 250 users, which covers a lot of groups, and there is nothing to train because you host it. Expect to cross that user count and Rocket.Chat’s uncapped Community Edition becomes the cleaner path. If your community is loud and asynchronous, spread across time zones, Zulip’s threading will do more for daily sanity than any privacy checkbox, and it happens to be private anyway. Reach for Element only when end-to-end encryption is a hard requirement and someone will own the deployment, because it asks the most of you. And if you are a small group that wants to buy one thing and never think about a vendor again, Campfire is $299 well spent. The one answer I would push back on is staying on Slack and telling members that the opt-out email covers them. It does not touch Slack AI, and it is not something they can verify for themselves.
Frequently asked questions
Does Slack train AI on my messages?
Not generative AI or chatbots. Slack states it does not build generative AI or large language models from customer data without opt-in consent. It does use your workspace content to train its own non-generative models for search and recommendations, and that runs by default until an owner emails Slack to opt out.
How do I opt a Slack workspace out of AI training?
A workspace owner or admin emails feedback@slack.com with the subject line “Slack Global model opt-out request” and the workspace URL. It applies to the whole workspace rather than a single channel, and it does not disable the Slack AI add-on when that has been enabled.
What is the best self-hosted Slack alternative for a community?
For a near drop-in feel, Mattermost. For large or fast-growing memberships with no user cap, Rocket.Chat. For busy asynchronous communities, Zulip. For encryption, Element. All four keep conversations on your own servers, so there is nothing for a vendor to train on.
Are open-source Slack alternatives actually free?
Self-hosting the software is free for Mattermost Team Edition, Zulip, Rocket.Chat Community Edition, and Element. You still pay for the server they run on, usually a few dollars a month for a small community, plus your own time for updates and backups. Campfire is the exception at $299 once, after which it is yours.
Can I keep my Slack message history when I move?
You can export Slack data, and several of these tools offer importers, though fidelity varies by plan and export format. Export your Slack workspace first, confirm the target platform can read that format, and run a test import before you ask members to switch.
Is self-hosting secure enough for a community?
It can be, but security becomes your job. You take on updates, patching, and backups that Slack would otherwise handle. Element adds end-to-end encryption on top, which protects messages even if the server itself is compromised. If nobody in the group can own basic server maintenance, a private hosted option may be the safer real-world choice.
Practical takeaway
Pick the tool that matches how your community already talks, then export your Slack history and run one test import before you announce anything. Stand the new server up, invite a handful of trusted members, and give it a week of real use. Once the archive imports cleanly and notifications work on people’s phones, send the invite to everyone. For more coverage of tools and the tradeoffs behind them, browse YouGottaRead’s Tech section. From that point on, no vendor is reading your community’s messages, because no vendor has them.
