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Interview with Cal Henderson CTO of Slack – Irish Tech News

Interview with Cal Henderson CTO of Slack – Irish Tech News

I recently spoke with Cal Henderson the CTO from Slack whilst he was visiting his Dublin office and got the latest on their products GRID and Shared Channels.

The last time I spoke with Michael Lopp VP of Slack, he was telling me about Shared Channels as it was in BETA.  How has it been received to the market?

Shared channels is still in BETA as there are still some things we want to add to it on the Enterprise side but we have seen a steady uptick to it so far.  It has been steadily growing week on week since we launched the BETA about a year ago.

We are seeing an increase in people using multiple shared channels to work with other businesses too.  We also use it ourselves of course!  Our customers have found it hugely useful to work with other companies like marketing and advertising agencies.  We have been told that because they don’t need to leave Slack and can do all of their messaging through it, the thread of conversation has been continual, and no one has needed to resort to email, which only confuses things.

“Shared Channels: Shared Channels bring the power of Slack, Channels and Apps to the work that happens between companies. Channels provide a secure, common space that makes working with external parties as straightforward and fluid as working with colleagues. By 2025, Slack believes that Channels will replace email as the primary way that people communicate and collaborate at work.”

When you first looked at creating this channel how did you test it to see what the demand for it was?

This kind of feature didn’t exist before so there was very little chance of people knowing exactly what they were asking/looking for.  However, we knew that it was very frustrating for people to drop down to email to work with people outside of Slack.  Once we had a very early Beta version we tried it with a handful of our customers to let them test it in that Alpha and see how it went for them.  They helped us tweak it and made it clear who they were talking to, because you need to know exactly when you’re talking to people within your company or a different company.

The way we go about building anything is by talking through it with our customers and understanding the problems we are solving for them and iterating it until we are happy with it.

Please can you tell us how GRID is getting on now?

GRID adoption is going really well.  The Enterprise and sales driven side didn’t really exist until a few years ago.  That has built up quite significantly is a large portion of our business is those large kind of businesses.  We have about 65% of the Fortune 100 are Slack customers, about 65% are FTSE 100, we have a lot of usage within large enterprise companies.  Our customers really vary from the small 3-5 people family business through to the largest companies in the world with hundreds of thousands of employees on Slack.

“Slack Enterprise Grid: Slack Enterprise Grid is designed to make everything people love about Slack more powerful for larger organizations. Slack Enterprise Grid connects unlimited workspaces for each department, office location, or team, and offers additional messaging capabilities shared across the entire company. On top of that, it provides the infrastructure needed to securely manage every workspace, user, and integration day to day”

Can you give us an example of some of those larger customers and how they would use Slack?

IBM, Target, Capital One so like very large companies in technology and not. About 60% of our users are in non-technical roles, so increasingly it’s not just used in technical companies but for people doing marketing, sales, finance and all roles across knowledge-work.  Here in Ireland we have tech customers like Stripe and Intercom and also Paddy Power.    In the UK we have Marks & Spencers and Monzo and English Heritage are a Slack customer.  Its definitely a case of we have moved beyond the smaller technical teams and now every vertical is represented.

Other businesses supported by Slack:

  • Fortune 500s: Capital One, eBay, IBM, 21st Century Fox, Oracle, Nordstrom
  • Financial Services: E*Trade, Moody’s Analytics, PayPal, Prudential, SoFi
  • Govt.: NASA’s Jet Propulsion Lab, US General Services Administration, US Department of State, UK Home Office, UK Ministry of Justice
  • Media: AP, Buzzfeed, CBS, Conde Nast, Dow Jones, Los Angeles Times, News Corp, New York Times, NPR, Oath, TIME, WSJ, 21st Century Fox
  • Retail/E-commerce: Birkenstock, Marks & Spencer, Net-a-Porter, Overstock.com, REI, Starbucks, Ticketmaster, Under Armour, Zappos
  • Tech: AirBnB, Box, Hyperloop Technologies, LinkedIn, Lyft, Pinterest, Samsung, SAP, SolarCity, Spotify, WeWork, Workday, Yelp!
  • Advertising/Marketing: Deloitte Digital, Ogilvy, R/GA
  • Non-profit/Education: Charity Water, Code for America, Dartmouth, Harvard, Johns Hopkins Sibley Innovation Hub, MIT, Teach for America
  • UK&I: ASOS, Centrica, English Heritage, Home Office, Intercom, ITV, Ocado, Marks & Spencer, Ministry of Justice, Paddy Power, Prudential, Sky, Starling Bank, Stripe

The workplace in general has been changing pretty fast in the last decade / five years.  Some of that is external factors like markets are moving faster than ever and a lot of that is driven by technology.  Also internal factors within companys.  Within the next year more than 50% of the workforce will be Millennials and they bring a different set of expectations with them to the tools that they use and to the work life balance that they expect.  Increasingly more work is becoming “knowledge-work” type jobs that are inherently team based.  If you look back at the last couple of decades of technology in the workplace, its has been very focussed in increasing individual productivity.  It has been all about how you can make each person more efficient and better at what they do.  With the explosion of Saas and the ability to target people in smaller and smaller roles with much more niche tools for like lead-scoring or marketing automation.  These are all helped with the productivity tools.  What we haven’t really seen over the years is group and team productivity tools and I think that this is the most unrealised upside of modern organisations.  We are well positioned to help businesses collaborate better with our tools.

The communication is around channels rather than by a one-to-one default.  These channels include a topic, a team, a project and that makes it much easier for people to find information within the channels.  Having information in a transparent format makes it much easier for people to participate in the communication and the message isn’t lost.

Work happens in a lot of various tools these days and with Slack we can help tie these things together and be the Collaboration Hub.  This means customer service, the sales force, the Google docs, behind the scenes comments can all be attributed to the one person from different departments and show a workflow to the people that need to see it.

Slack is also very easy to search and made all the easier for new members of staff when they have a query, they can simply put the question in the Slack search bar and find answers to similar previously asked questions.  Even when people leave the organisation, their responses and questions remain so no bit of knowledge is ever lost unless it is removed.

What is next for Slack?

Well we are really focussing on growth from here on.  There is currently 8 million active daily users at the moment but there are still lots of “knowledge-workers” in the region of 600 million and this is growing, that could benefit from Shared Channels or GRID.  We are only scratching the surface at the moment.

I believe in the next 7 years business will be conducted on a shared channel basis and we want to be the ones to make this model the norm.  As long as we don’t muck it up, we will be the generation leader in this.

KEY STATS (As of May 8, 2018)

  • 8M+ Daily Active Users (DAU)
  • 3M+ paid users, 70,000+ paid teams, including:
  • 65% of the Fortune 100 companies
  • Half of DAU are outside of North America – top five countries: Japan, United Kingdom, Germany, France, India
  • In more than 100 countries
  • 1200+ employees across 9 offices

PLATFORM (As of May 17, 2018)

  • 8.8M+ apps installed
  • 200,000+ weekly active developers building on the platform (including internal integrations)
  • 1500+ apps in the App Directory
  • 94% of our paid teams on Slack actively use apps


Cal Henderson is the co-founder and CTO of Slack. He is an experienced technology leader, having previously built and led the engineering team at Flickr, through its acquisition by Yahoo.

As a popular speaker on engineering scalability, he authored the best-selling O’Reilly Media book “Building Scalable Websites”. He was a pioneer in the use of web APIs, and created the basis for oAuth and oEmbed, now used by YouTube, Twitter, and many others.

Cal has a Bachelor of Computer Science from the University of Central England, and was involved in London’s early online community through his work with the early digital community B3ta and his personal blog iamcal.com, which he has run for over 15 years. Cal now resides in San Francisco.


Slack is the leading global collaboration hub that makes people’s working lives simpler, more pleasant and more productive. From global Fortune 100 companies to corner markets, businesses and teams of every kind use Slack to bring the right people together with all the right information. Slack is headquartered in San Francisco CA, and has nine offices around the world. For more information on how Slack makes teams better connected, visit slack.com.