Slack leads messaging core 6.5 to 2.5, encryption and access 5.3 to 2.3, governance and discovery 5.5 to 2.5 and sovereignty 2.8 to 0.7 — each a six-to-zero lean for Slack — and integrations 5.8 to 3.8, five judges leaning Slack with one tie. Microsoft Teams (Chat) is ahead on pricing transparency alone, 4.0 to 3.7: three judges lean Teams, one leans Slack, two tie, and its verdict cites add-on prices published exactly — Teams Premium at 8,70 € per user per month, VAT excluded — where the Slack verdict records no per-user price, leaving the annual invoice not computable. Deployment control nearly ties, 1.0 to 1.3, four ties and two judges leaning Slack. The listed sovereignty attributes match on IE jurisdiction, US by default residency and US CLOUD Act reach exposure, with ownership unknown for Teams and foreign-controlled for Slack. Persona-weighted totals span 1.8 to 3.3 for Teams and 4.0 to 4.9 for Slack.
Choose Microsoft Teams (Chat) if
You must compute the annual invoice before signing — pricing transparency leans Microsoft Teams (Chat) three judges to one, with add-on prices published exactly, while the Slack verdict records no per-user price and an annual invoice that is not computable.
Your finance approval needs exact public per-user prices — Teams Premium at 8,70 € per user per month and Microsoft 365 Copilot Business at 18,20 € per user per month, VAT excluded, are published.
Your vendor policy screens out foreign-controlled ownership — the sovereignty attributes list Slack as foreign-controlled and record Microsoft Teams (Chat)'s ownership as unknown.
Your evaluation weights published pricing most heavily — pricing transparency is the one criterion where Microsoft Teams (Chat) leads on means, 4.0 to 3.7, and on leans, three judges to one.
Choose Slack if
You weigh messaging core first — it leans Slack six judges to zero, mean 6.5 to 2.5, credited for channels, Slack Connect cross-organisation rooms, AI search over stored knowledge and unlimited message history from Pro.
Your security review scores encryption and access heavily — that criterion leans Slack six judges to zero, mean 5.3 to 2.3.
You must run retention, legal hold and DLP — governance and discovery leans Slack six judges to zero, mean 5.5 to 2.5.
Your platform engineers want a buildable surface — integrations leans Slack five judges to one tie, mean 5.8 to 3.8, with the platform engineer crediting 1.7 million weekly active apps.
You need Germany data residency — sovereignty leans Slack six judges to zero, mean 2.8 to 0.7, and the verdict records Germany residency purchasable from Business+.
Read this comparison as one judge. Each weighs the same scores by what they care about.
The Security Officer
Assumes the archive will one day be read by someone it was not meant for. Wants end-to-end encryption that ordinary users survive, device verification, sessions an admin can revoke, and a plain statement of what the vendor cannot decrypt.
Microsoft Teams (Chat)
Slack
This judge's pick
Criterion by criterion
Channels, threads & search
Microsoft Teams (Chat)
The captured pages confirm chat and channels as a solution area, plus file sharing through SharePoint and per-user cloud storage of 1 TB or 10 GB depending on plan. We found no public information in the captures on threading, mentions, full-text search across history, message editing history, or channel lifecycle, so I cannot place the daily surface above the basic channel-and-attachments level.
Slack
Channels, cross-organisation Slack Connect with boundaries, search over all stored company knowledge, and unlimited message history on paid plans with the free tier's 1-year cap documented clear the anchor-5 bar and half of anchor-8. But editing history, pinned/saved items, filtered search and human-readable conversation export are nowhere evidenced, so I stop short of 8.
Encryption & access control
Microsoft Teams (Chat)
Encryption of meetings, chats, calls and files appears only as a feature bullet on a plan comparison page, with no documented mechanism, no statement of who holds the keys, and no end-to-end mode, device verification, or admin-revocable sessions anywhere in the captured pages. The privacy statement says user data may be used to develop and train Microsoft's AI models, which is the opposite of a plain statement of what the vendor cannot read, though it also notes customer agreements for enterprise and developer products take precedence over the statement.
Slack
Encryption at rest and in transit with vendor-held keys, plus SSO, 2FA, SCIM, information barriers and channel posting permissions — that is anchor-5 territory with an EKM add-on as partial key custody. No end-to-end encryption, no device verification, no session management an admin can revoke, and no statement of what Slack cannot decrypt: an archive anyone at the vendor with the keys can read is not the one I want.
Retention, discovery & co-determination
Microsoft Teams (Chat)
Compliance and data protection are routed to the Microsoft Purview suite, which requires a Microsoft 365 E3 licence, and the captured pages document none of its mechanisms — no per-channel retention, no discovery export format, no audit trail, and no organisation-wide switch for presence or activity analytics. The only retention-adjacent statements are that all associated data is deleted on subscription cancellation and that time, date and participants of communications are collected as metadata.
Slack
Retention configurable at workspace, channel or other level, legal hold and audit logs named, DLP on every plan — good bones for a legal object. But the evidence never evidences a discovery export format, capture of edits and deletions, or any switch for activity analytics, so I cannot certify the subpoena half of anchor-8.
Deployment & data custody
Microsoft Teams (Chat)
Everything captured describes cloud subscription plans; we found no public information on a self-hosted edition, an open-source or source-available server, federation, or a documented export of the workspace archive including files and metadata. Custody is further concentrated by the statement that personal data may be stored and processed in the United States and in any jurisdiction where Microsoft or its service providers operate.
Slack
Cloud-only and proprietary, from a San Francisco vendor; the evidence documents no self-hosting, no federation and no archive export format at all — the only data-getting-out rights are GDPR access requests. Custody of the archive never leaves the vendor, and an exit path is entirely unevidenced, which is close to the anchor-0 floor.
Integrations & extensibility
Microsoft Teams (Chat)
Over 250 integrated business apps and the ability to build custom chatbots with Copilot Studio are shown, with a free version of Microsoft Entra ID in all three plans for identity. We found no public information in the captures on a documented REST API, incoming or outgoing webhooks, slash commands, event subscriptions with retries, SCIM provisioning, rate limits, or a sandbox, which keeps this below a documented developer platform.
Slack
A genuine platform: buildable solutions by click or code, 1.7 million weekly active apps with named native integrations, SCIM provisioning, SSO, and workspace-level control over third-party services. Rate limits, a sandbox, API versioning and auditable app permissions are unevidenced, which keeps it below anchor-8.
European sovereignty
Microsoft Teams (Chat)
Microsoft is a United States vendor, and the privacy statement says personal data may be stored and processed in the user's region, in the United States and in any jurisdiction where Microsoft, its affiliates, subsidiaries or service providers operate. We found no public information on EU data residency, an EU contracting entity, or a published subprocessor list; the only cross-border safeguards named are the EU-US, UK-extension and Swiss-US data privacy frameworks.
Slack
Germany data residency exists but only as an upsell from Business+, the contracting entity is US-based Salesforce, the LLM processing sits in a Slack AWS private cloud with no region named, and the subprocessor list is unpublished — that is precisely the anchor-3 shape: content residency offered while the rest of the chain stays opaque and non-EU.
Pricing transparency
Microsoft Teams (Chat)
Add-on prices are public and exact — Teams Premium at 8,70 € per user per month and Microsoft 365 Copilot Business at 18,20 € per user per month, annual billing with automatic renewal, prices excluding VAT — with storage limits, a 7-day pro-rated refund right and trial auto-conversion all stated. But we found no public information on per-user prices for the base plans, and the compliance and data-protection capabilities sit in the Microsoft Purview suite requiring Microsoft 365 E3, whose price we found no public information on, so the invoice for a compliance-minded buyer is not computable from these pages.
Slack
The tier map is documented — SSO on every plan including free, Germany residency from Business+, unlimited history from Pro — but not one per-user price, billing period, VAT treatment or Enterprise Key Management add-on price appears in the evidence. A buyer can see which tier they need but cannot compute the annual invoice, and retention controls are explicitly plan-dependent with Enterprise+ pricing absent.
Sovereignty, side by side
Dimension
Microsoft Teams (Chat)
Slack
Legal entity
Not determined
Not determined
Ownership
Not determined
Not determined
Data residency
Not determined
Not determined
Subprocessors
Not determined
Not determined
Facts, side by side
Only facts both products carry under the same definition — anything else would not be a fair row.