Slack (software)
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Last reviewed
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Slack is a workplace messaging platform owned by Salesforce. It runs the day to day chatter of a large fraction of software companies, including most of the AI labs that ship the products this wiki covers. The app organizes conversation into persistent channels, threads, and direct messages, layered with file sharing, audio and video huddles, an app marketplace, and a developer platform that has become one of the most common surfaces for plugging in AI agents, LLM assistants, and bots.
Slack was launched publicly on February 12, 2014 by Tiny Speck, a startup founded in 2009 by Stewart Butterfield, Eric Costello, Cal Henderson, and Serguei Mourachov. The team had been building a massively multiplayer online game called Glitch. The game flopped, the internal chat tool the team had built to keep itself coordinated did not, and that pivot ended up creating one of the fastest growing business software companies in history. Slack went public on the New York Stock Exchange in a direct listing on June 20, 2019 under the ticker WORK, and was acquired by Salesforce on July 21, 2021 in a cash and stock deal valued at approximately $27.7 billion.
Since the Salesforce deal closed, Slack has been pulled deeper into the broader Salesforce AI strategy. Slack AI, a paid generative AI add on, became generally available on February 14, 2024 with channel recaps, thread summaries, and AI search answers. Salesforce's Agentforce platform, the company's enterprise AI agent framework, runs inside Slack as one of its primary user surfaces. Outside the Salesforce stack, Slack is also one of the most common third party integration targets for AI products from OpenAI, Anthropic, and frameworks like LangChain, and is one of the reference servers for the Model Context Protocol.
| Field | Value |
|---|---|
| Original developer | Tiny Speck (2009 to 2014) |
| Current owner | Salesforce (since July 21, 2021) |
| Founders | Stewart Butterfield, Eric Costello, Cal Henderson, Serguei Mourachov |
| Headquarters | San Francisco, California |
| Launched | August 2013 (preview), February 12, 2014 (general availability) |
| IPO | NYSE direct listing, June 20, 2019, ticker WORK |
| Acquired | December 1, 2020 announced; July 21, 2021 closed |
| Acquisition value | About $27.7 billion in cash and stock |
| Key product lines | Slack core, Slack Connect, Slack AI, Agentforce in Slack |
Tiny Speck was incorporated in 2009 in Vancouver, British Columbia. Stewart Butterfield was running it. He had co-founded Flickr a few years earlier, sold it to Yahoo in 2005, then left to start something new. Cal Henderson and Serguei Mourachov had also worked on Flickr; Eric Costello was part of the team Butterfield assembled to chase his next idea. The next idea was a game.
The game was called Glitch. It was a browser based 2D massively multiplayer thing with a soft, hand drawn art style and a deliberately weird sense of humor. There was no combat. You collected, crafted, gardened, and gossiped. Tiny Speck raised about $17 million across angel, Series A from Accel and Andreessen Horowitz, and Series B rounds to fund development. Glitch launched on September 27, 2011, then "unlaunched" in November to keep iterating, then officially shut down on December 9, 2012. The team could not get the audience numbers to work. It was, as Butterfield later admitted in his now widely circulated farewell email to investors, a failure.
While building Glitch, the team had been using a homegrown internal communication tool. They had distributed offices in Vancouver, San Francisco, and New York, and IRC and email were not cutting it. The internal tool grew into something the engineers themselves preferred to use. After Glitch died, Butterfield and the founding team looked at what they had left, the internal chat tool, and decided that was the actual company. The pivot is now part of startup folklore, partly because it worked, partly because Butterfield is unusually candid about it.
Slack went into preview release in August 2013. The team avoided the word "beta" because they thought it suggested unreliability. Instead they ran a request for invites approach paired with press coverage. About 8,000 companies signed up in the first 24 hours, a figure Butterfield himself cited at the time and that VentureBeat reported in early coverage. Two weeks in, sign ups passed roughly 15,000.
The official, paid public launch came on February 12, 2014. By that point Slack had a freemium business model: free workspaces with limited message history, and paid tiers for larger teams that wanted full search, more integrations, and admin controls. The product caught on inside small tech teams first, then spread up market.
Growth was steep. In April 2015 Slack reported 750,000 daily active users, with about 200,000 of those on paid plans. By mid 2015 the platform crossed roughly one million daily active users. By April 2017, the company put daily active users at around 8 million, with about 2 million paid. In May 2018 Slack reported 8 million daily active users with 3 million paid, and at IPO filing in April 2019 it claimed more than 10 million daily active users across more than 600,000 organizations in over 150 countries.
The name, Butterfield said in 2012 and has repeated since, comes from a backronym: Searchable Log of All Conversation and Knowledge. The codename during development was "linefeed." Slack Technologies, the new corporate name, was adopted in August 2014.
On June 20, 2019, Slack listed its shares directly on the New York Stock Exchange under the ticker WORK. The NYSE set a reference price of $26 per share. The stock opened the next morning at $38.50, almost 50% above that reference, and closed its first day around $38.62, putting Slack's market capitalization at about $19.5 billion.
The direct listing was unusual. In a traditional IPO, a startup hires investment banks to underwrite an offering, line up new buyers, and raise fresh capital. Slack did not raise new capital at listing. Existing shareholders, employees, and early investors simply became free to sell, with banks acting as advisors rather than underwriters. Spotify had used the same approach in 2018. After Slack, direct listings became a more visible, if still rare, alternative for well known consumer or enterprise tech companies that did not need new cash.
The public market years were short and not entirely smooth. Slack had ridden into the listing with strong growth, but Microsoft had launched Microsoft Teams in November 2016 and was bundling it into Office 365 at no extra cost. By the time Slack was on the NYSE, Microsoft was claiming Teams had passed Slack on daily active users, a claim Butterfield publicly disputed using different definitions of "active." The pandemic in early 2020 accelerated remote work and helped both products, but the bundling math kept favoring Microsoft.
On December 1, 2020, Salesforce announced a definitive agreement to acquire Slack Technologies for approximately $27.7 billion in cash and stock. The deal closed on July 21, 2021, after the U.S. Department of Justice ended its antitrust review without action. It was the largest acquisition in Salesforce's history.
Slack continued to operate as a Salesforce subsidiary, retaining its brand and headquarters. Butterfield stayed on as CEO until December 5, 2022, then departed. Lidiane Jones ran Slack from December 2022 until November 2023. Denise Dresser took the role from November 2023 until December 2025. Rob Seaman has held the position since.
Salesforce CEO Marc Benioff has consistently framed Slack as the new "interface" or "front end" for the Salesforce stack: a place where workers receive notifications, query data, and increasingly hand off tasks to AI agents that act on Salesforce customer relationship management records behind the scenes.
The core unit in Slack is the channel: a persistent, named room that anyone in the workspace (or invited to it) can read, search, and post in. Channels can be public or private, with the difference visible from the channel icon. Replies can be threaded under a parent message so a side conversation does not flood the main channel. Direct messages are one to one or small group chats, also persistent and searchable.
This sounds simple, but the choice to default to persistent, searchable, channel based communication was a sharp departure from the email and instant messenger norms of the early 2010s. Companies that adopted Slack typically migrated a lot of internal email volume into channels, with mixed effects on attention and information overload that engineers and managers still argue about today.
Huddles are Slack's lightweight audio and video calls. They started as audio only in 2021, then added video, screen sharing, drawing, and reactions. Paid plans support up to 50 people in a huddle. Huddles intentionally compete with quick Zoom or Meet calls for ad hoc team conversations, and Slack has been adding AI features specifically tuned to them.
Canvas is a long form document surface inside Slack, launched in 2023. A canvas can be attached to a channel, direct message, or huddle, and lives alongside the chat. It supports rich text, embedded files, checklists, and live data from connected apps. Canvas is positioned as competition for tools like Notion or Confluence for short, work in progress documents, with the idea that the document and the conversation about it should live in the same place.
Workflow Builder lets non developer users wire up multi step automations: a form submission triggers a message, a message triggers a follow up question, an approval routes back to a manager, and so on. It originally shipped in 2019 with simple branching, and has been expanded over time with more steps, conditional logic, and connectors to Salesforce and third party apps.
Slack Connect, launched in 2020, lets users create channels that span multiple organizations. Two companies that both use Slack can have a shared channel for their account managers and engineers, instead of routing every interaction through email. It is also the channel through which a lot of B2B virtual assistant and agent collaboration is starting to appear: an external Agentforce agent or partner bot can sit in a Connect channel and act as a shared point of contact between two companies.
The Slack platform is the part most developers interact with. It includes:
| Component | Purpose |
|---|---|
| Web API and Events API | Read and write Slack data, subscribe to events |
| Slash commands | Trigger app actions with /command syntax |
| Block Kit | UI framework for buttons, menus, modals, and message layouts |
| Bolt SDKs | Higher level frameworks for JavaScript, Python, and Java |
| Workflow steps from apps | Custom steps inside Workflow Builder |
| Socket Mode | WebSocket connection for apps behind firewalls |
Block Kit is a JSON UI description language. You declare blocks (sections, dividers, actions, inputs) and Slack renders them as interactive messages or modals. Bolt is the framework that wraps the Slack APIs in idiomatic SDKs and handles OAuth, request signing, retries, rate limits, and event routing for you. Most production Slack apps today are built on Bolt.
The app marketplace, called Slack Marketplace, lists thousands of third party apps. The mix is heavy on enterprise SaaS (GitHub, Jira, Asana, Notion, Salesforce of course), monitoring and incident tools (Datadog, PagerDuty, Opsgenie, FireHydrant), and increasingly AI integrations.
Slack's pricing has shifted several times since the Salesforce acquisition. The current public structure looks roughly like this. Prices are list prices in U.S. dollars, monthly per active user when billed annually, and may differ for enterprise contracts.
| Plan | Approximate price | Notable features |
|---|---|---|
| Free | $0 | 90 days of message history, 10 app integrations, 1:1 huddles |
| Pro | About $7.25 per user per month | Unlimited history, group huddles, Slack Connect, unlimited apps |
| Business+ | About $12.50 per user per month | SAML SSO, data exports, 99.99% uptime SLA |
| Enterprise Grid | Custom | Multi workspace org, advanced compliance, HIPAA, eDiscovery |
| Slack AI add on | Custom (paid add on) | Channel recaps, thread summaries, AI search answers |
| Agentforce in Slack | Custom (Salesforce contract) | Salesforce agents in Slack flow of work |
The free tier originally offered access to a rolling 10,000 message history. Slack changed it in 2022 to a 90 day window of full history instead, which was unpopular with hobbyist and open source users but more straightforward to explain.
Slack's first major generative AI launch was Slack AI, announced in 2023 and made generally available on February 14, 2024 as a paid add on for Pro, Business+, and Enterprise Grid plans.
Slack AI shipped with three core features:
A notable design choice is that Slack AI runs on infrastructure managed by Slack itself, with prompts and customer content not sent to external LLM providers in a way that would let those providers train on customer data. Slack is fairly explicit about this in its trust and data management documentation.
Later additions have included translations, huddle notes (an automatic written summary of a huddle's discussion and action items, expanded in mid 2025), and tighter integration with Salesforce records via Agentforce.
Slack AI is positioned somewhat differently from a horizontal assistant like ChatGPT or Microsoft Copilot. The pitch is narrower: it answers questions about your own Slack workspace, with permissions inherited from the workspace itself. The trade off is less flexibility but a much cleaner story on data boundaries.
In May 2023, before Slack AI itself shipped, Salesforce announced a broader umbrella called Slack GPT. The branding has shifted since then, but the core idea was that Slack would integrate Salesforce's Einstein GPT (later Einstein 1) and partner LLMs, letting customers wire conversations and workflows to whichever model they wanted. ChatGPT for Slack, an OpenAI app sitting inside Slack, was demoed in March 2023 and was an early example of that direction.
In 2024, Salesforce rebranded much of its agent strategy as Agentforce, which Marc Benioff has called the company's third major platform shift after Sales Cloud and Einstein. Agentforce in Slack went into beta in October 2024, and Agentforce 2.0 in early 2025 made Slack the default user facing surface for those agents.
Agentforce in Slack works roughly like this. An admin sets up a Salesforce agent (e.g. a customer support agent or an employee help desk agent), grants it permissions, and exposes it inside Slack. Employees can @mention the agent in a channel or direct message, and the agent can answer questions, take multi step actions, query Salesforce records, and post results back into the conversation. Agentforce has access to a Slack-specific action library so it can do things employees normally do in Slack: open canvases, post messages, react with emojis, schedule follow ups, route tasks, and so on.
Salesforce ships several pre built agent templates for Slack including a Customer Insights Agent, an Employee Help Agent, and an Onboarding Agent, with custom templates available through the broader Agentforce platform. At Dreamforce 2024, Salesforce reported that customers had built more than 10,000 agents on Agentforce in the run up to and during the conference.
Even outside the Salesforce stack, Slack has become one of the standard places to host AI agents and assistants. There are a few reasons.
First, Slack is already where work happens. Engineers, sales people, and support staff are watching the same channels for human conversation, so it is the lowest friction place for an agent to deliver an answer. Second, the platform APIs are relatively mature and well documented, with first party SDKs and a marketplace that handles distribution. Third, the permission model is reasonably clear: an agent runs as a Slack app, with explicit OAuth scopes per workspace.
Concrete examples:
This last point is worth stating plainly. Slack is the daily driver for a sizable fraction of the AI engineering workforce. That fact has shaped product decisions on both sides: Slack ships features designed for engineering and AI teams, and AI vendors prioritize Slack as a launch integration because their own employees are already using it.
In May 2024, a Hacker News thread surfaced existing language in Slack's privacy policy stating that Slack analyzed customer data, including messages, content, and files, to train AI and machine learning models. The default was opt in, and the only way to opt out was to email Slack with a specific subject line.
The response online was sharp. Critics argued that the policy was buried, the opt out friction was unreasonable, and that the language conflated training of generative models with training of older non generative recommenders. Slack publicly clarified within days that customer data was not being used to train Slack AI's generative features, which run on hosted models that Slack does not retrain on customer content. The data in question was being used for non generative models behind features like emoji and channel recommendations and basic search ranking. Slack updated its privacy principles to make this clearer and to reduce ambiguity in the language.
The episode became a frequently cited example in 2024 discussions of how SaaS vendors should communicate data use for ML, especially after similar opt out rather than opt in flaps at LinkedIn and other consumer and enterprise platforms.
Slack's main competitor is Microsoft Teams, launched in November 2016 and bundled into Microsoft 365. Teams won most of the large enterprise license footprint on the strength of that bundle, especially during the COVID era spike in remote work. Slack's argument has consistently been that depth, openness, and developer ecosystem matter more than headline seat count. The reality is that many large companies run both, with Teams as the default for video and Slack as the default for engineering and product chat.
Discord is structurally similar to Slack but oriented at communities rather than enterprises. Some startups and open source projects use Discord in place of Slack because the free tier is more generous and voice chat is built in. Discord has experimented with monetization for businesses but has not seriously pursued the enterprise segment.
Zoom competes for huddles and meetings, and has a Zoom Team Chat product that overlaps with Slack's text features. The footprint there is much smaller than Teams or Slack.
Google Chat, bundled with Google Workspace, plays a role similar to Teams' bundle for organizations standardized on Google. Mattermost and Rocket.Chat are open source self hosted alternatives that show up in regulated environments.
| Product | Owner | Launched | Default user | Notable AI |
|---|---|---|---|---|
| Slack | Salesforce | 2013 / 2014 | Engineering, product, support | Slack AI, Agentforce in Slack |
| Microsoft Teams | Microsoft | November 2016 | Office 365 enterprises | Microsoft 365 Copilot |
| Discord | Discord Inc. | May 2015 | Communities, gaming | Limited bot ecosystem |
| Zoom Team Chat | Zoom | 2017 (chat) | Zoom users | AI Companion |
| Google Chat | 2017 | Google Workspace orgs | Gemini in Workspace |
Slack moved its headquarters into Salesforce Tower in San Francisco by February 2023, consolidating with its parent. It remains a wholly owned subsidiary of Salesforce, with separate go to market and engineering organizations but increasing integration with the rest of the Salesforce stack, especially the Customer 360 data layer and the Einstein and Agentforce AI platforms.
The brand has stayed mostly intact under Salesforce. The product still ships as Slack, the Slackbot mascot still talks to new users in onboarding, and the developer platform still goes by the same names. The biggest visible change is the gravity of AI features and the steady absorption of Slack into the bigger Salesforce "flow of work" pitch.