I have made the call on both sides of this decision in the past five years. A 40-person engineering team I advised in 2023 lived in Teams for three years and finally migrated to Slack after a Copilot add-on price hike pushed the yearly bill past $60,000. A 60-person product team in 2025 moved from Slack to Teams because Microsoft bundled Teams back into M365 and the TCO dropped in a single quarter.
What changed between those two decisions is what this article is about. In November 2025, Microsoft re-bundled Teams into Microsoft 365 for all business plans. In the same window, Slack folded its AI features into paid plans and moved off standalone AI add-ons. In July 2026, M365 pricing went up across the board. All three changes collapsed the pricing gap.
From a product perspective, the 2026 call is no longer about who is better. It is about which TCO profile fits your team, which AI posture you can actually afford, and whether you can absorb the ecosystem lock-in.
The three dimensions that decide it in 2026
Forget feature checklists. In 2026, three things decide the call, and they line up in this order:
1. AI pricing
Microsoft Teams ships Copilot bundled with M365 Business Premium at $32 per seat per month, which now covers Copilot Chat, Copilot in Teams, and Copilot in Excel. Standalone Teams plus a separate Copilot seat adds roughly $18 per seat on top. Slack, on the other hand, folded AI features into Pro at $8.75, Business+ at $12.50, and Enterprise Grid at custom pricing. There is no standalone Slack AI add-on to buy.
From a product perspective, this is the biggest change in three years. Before 2026 you had to budget for a Copilot add-on; in 2026 the AI cost is embedded in the base seat, and the total cost depends on which base you pick.
2. Ecosystem lock-in
If your team is already paying for M365, Teams is nearly free marginal cost. If your team lives in Slack-native workflows and has custom Slack apps, migrating off means rebuilding integrations. Both directions of the fence are expensive, but the price depends on where you stand.
The practical test: list the top five integrations your team actually uses. If four are M365-native, Teams is the right call. If three are Slack-native, Slack is the right call. If it is a toss-up, look at the third dimension.
3. External collaboration
Slack Connect is the industry default for cross-company collaboration. Customers, agencies, and vendors are more likely to be on Slack than on Teams. If external collaboration is a core part of your business, that single factor can decide the call, regardless of internal preferences.
Concrete example: a SaaS product team I advised in 2025 had 14 active Slack Connect channels with customers and agencies. Moving to Teams would have meant asking each customer to switch tools, which was not feasible. They stayed on Slack.
TCO at 10, 50, and 200 seats
Let us put real numbers on this. All prices are 2026 US list prices. Annual commitment, USD, per-seat annual cost, then multiplied by seat count.
| Component | 10 seats | 50 seats | 200 seats |
|---|---|---|---|
| Slack Pro (base) | $1,050 / year | $5,250 / year | $21,000 / year |
| Slack Business+ (base) | $1,500 / year | $7,500 / year | $30,000 / year |
| Slack AI | included | included | included |
| M365 Business Premium + Teams | $3,840 / year | $19,200 / year | $76,800 / year |
| M365 + Copilot in Teams | included | included | included |
| Copilot add-on (standalone) | $2,160 / year | $10,800 / year | $43,200 / year |
| Effective total with AI | $1,500 / year | $7,500 / year | $30,000 / year |
A few things jump out:
- At 10 seats, Slack is roughly 40% cheaper than Teams. Both platforms are within the same budget band.
- At 50 seats, the gap narrows. Teams cost $19,200 per year versus Slack Business+ at $7,500, but that $11,700 gap only exists if the team does not already pay for M365 elsewhere.
- At 200 seats, the M365 baseline becomes the dominant number. Slack Business+ is $30,000 per year. M365 Business Premium is $76,800 per year, and adding a Copilot add-on on top is $43,200 more. If you do not already pay for M365, do not add Teams for the sake of Copilot.
AI feature availability comparison
AI is where the two products diverge the most in 2026. Below is the AI feature availability comparison table I use with every team.
| AI feature | Microsoft Teams (with Copilot) | Slack (Pro / Business+) |
|---|---|---|
| Meeting recap | Yes, full recap | Yes, via AI huddles |
| Action item extraction | Yes, deep integration with Planner and To Do | Yes, posts to channel |
| Chat summarisation | Yes, Copilot in chat | Yes, thread summary |
| File summarisation | Yes, across Office suite | Yes, across uploaded files |
| Custom AI assistant | Copilot Studio, paid | Slack Assistant, included on Business+ |
| Historical Q&A | Yes, in the tenant context | Yes, over full workspace history |
Teams has the deeper AI surface because Copilot Studio is a real product with a paid developer program. Slack has the faster in-chat experience because its AI is built for messages, not documents. If your team spends more time in chat, Slack wins. If your team spends more time in documents, Teams wins.
Hidden costs nobody tells you about
Three hidden costs come up in every evaluation call:
- Copilot add-on price creep. Before 2025, Copilot was a $30 add-on. In 2026, the add-on is $18 for existing M365 customers, but the base M365 price went up in July 2026 by an average of 11%. The add-on is cheaper, the base is more expensive.
- Slack free-plan history truncation. Slack free plan keeps only the last 90 days of history. Migrating a workspace to free to save on licence cost deletes three to four years of searchable context for free-plan users. If your team needs that history, you cannot save your way out.
- Slack auto price increases. Slack enterprise contracts typically include a year-over-year price escalator of 5-9%, which can exceed $10,000 per year at 200 seats. This is buried in the MSA, not the pricing page. Read the escalator clause carefully before signing.
Pros and cons, side by side
| Tool | Pros | Cons |
|---|---|---|
| Microsoft Teams | Bundled with M365, Copilot included, deep Office integration, enterprise-grade compliance | Requires M365 baseline, less flexible for external collaboration, Copilot add-on is expensive if you are not already paying |
| Slack | Fast chat UX, Slack Connect for external teams, 1000+ integrations, mature workflow automation | AI features only on paid plans, 90-day history truncation on free plan, hidden annual escalator clauses |
Neither tool is objectively better. Both are defensible if the surrounding assumptions hold. What kills a decision is ignoring the surrounding assumptions.
12-step migration checklist
Migration is not a switch. It is a two-month choreography.
Teams to Slack
| Step | Action | Owner |
|---|---|---|
| 1 | Freeze new Teams channel creation for two weeks | IT |
| 2 | Export channel and file inventory from Teams | IT |
| 3 | Map Teams channels to new Slack channels | Team lead |
| 4 | Import file history via Slack importer, or link Drive where feasible | IT |
| 5 | Install GitHub, Jira, Figma, Linear, and Datadog integrations | Dev lead |
| 6 | Pilot with 10 people for one week | Team lead |
| 7 | Publish a one-page Slack cheat sheet | Ops |
| 8 | Run a 15-minute Slack walkthrough for the whole team | Team lead |
| 9 | Full cutover on a Monday morning | IT |
| 10 | Decommission Teams permissions on core integrations | IT |
| 11 | Archive unused Teams channels and revoke licences | IT |
| 12 | Post-migration retro after 30 days | Team lead |
Slack to Teams
The reverse path is similar but takes longer because Teams has a steeper onboarding curve for chat-native teams. Use the same 12-step framework, but expect an additional two-week onboarding sprint where engineers and PMs learn how to do meetings, huddles, and channel announcements in Teams.
Which one should you pick in 2026
Use this decision tree:
- If you already pay for M365 Business Premium and Copilot is not a must-have add-on, keep Microsoft Teams. The bundle is real, the TCO is real, and the switch cost exceeds the savings for most teams under 100 seats.
- If you need Copilot specifically, evaluate the $18 add-on against the $32 all-in M365 Business Premium seat. Sometimes paying $18 on top of $12.50 is cheaper than the $32 bundle.
- If your team lives in Slack-native workflows and external collaboration is high, migrate to Slack Business+. The AI features are included, and the migration cost amortises over 12-18 months.
- If your team is under 20 seats and price-sensitive, pick Slack Pro. $8.75 per seat with AI included is hard to beat in 2026.
The verdict I give in 2026 is not to pick one forever. It is to pick the tool that matches your current TCO profile, revisit every 12 months, and budget for the migration cost regardless of direction.
That is how every serious evaluation ends. The tools converge, but the ecosystem does not.