375 Beale Street, Suite 300
San Francisco, California 94105
(Address of principal executive offices) (Zip Code)

Indicate by check mark if the registrant is a well-known seasoned issuer, as defined in Rule 405 of the Securities Act: Yes o No ý

Indicate by check mark if the registrant is not required to file reports pursuant to Section 13 or 15(d) of the Act: Yes o No ý

Indicate by check mark whether the registrant (1) has filed all reports required to be filed by Section 13 or 15(d) of the Securities Exchange Act of 1934 during the preceding 12 months (or for such shorter period that the registrant was required to file such reports), and (2) has been subject to such filing requirements for the past 90 days. Yes ý No o

Indicate by check mark whether the registrant has submitted electronically and posted on its corporate Web site, if any, every Interactive Data File required to be submitted and posted pursuant to Rule 405 of Regulation S-T (§232.405 of this chapter) during the preceding 12 months (or for such shorter period that the registrant was required to submit and post such files). Yes ý No o

Indicate by check mark if disclosure of delinquent filers pursuant to Item 405 of Regulation S-K is not contained herein, and will not be contained, to the best of registrant's knowledge, in definitive proxy or information statements incorporated by reference in Part III of this Form 10-K or any amendment to this Form 10-K. o

Indicate by check mark whether the registrant is a large accelerated filer, an accelerated filer, a non-accelerated filer, or a smaller reporting company. See the definitions of "large accelerated filer," "accelerated filer" and "smaller reporting company" in Rule 12b-2 of the Exchange Act.

Indicate by check mark whether the registrant is a shell company (as defined in Rule 12b-2 of the Exchange Act). Yes o No ý

The aggregate market value of stock held by non-affiliates as of June 30, 2016, was $422.4 million based upon $36.50 per share, the closing price for such date on the New York Stock Exchange.

On January 31, 2017, the registrant had 51,571,092 shares of Class A common stock and 35,962,651 shares of Class B common stock outstanding.

Portions of the registrant's definitive Proxy Statement for the 2017 Annual Meeting of Stockholders are incorporated herein by reference in Part III of this Annual Report on Form 10-K to the extent stated herein. Such Proxy Statement will be filed with the Securities and Exchange Commission within 120 days of the registrant's fiscal year ended December 31, 2016.

Twilio Inc.

Annual Report on Form 10-K

For the Fiscal Year Ended December 31, 2016

TABLE OF CONTENTS

This Annual Report on Form 10-K contains forward-looking statements within the meaning of Section 27A of the Securities Act of 1933, as amended, and Section 21E of the Securities Exchange Act of 1934, as amended, which statements involve substantial risks and uncertainties. Forward-looking statements generally relate to future events or our future financial or operating performance. In some cases, you can identify forward-looking statements because they contain words such as "may," "will," "should," "expects," "plans," "anticipates," "could," "intends," "target," "projects," "contemplates," "believes," "estimates," "predicts," "potential" or "continue" or the negative of these words or other similar terms or expressions that concern our expectations, strategy, plans or intentions. Forward-looking statements contained in this Annual Report on Form 10-K include, but are not limited to, statements about:

We caution you that the foregoing list may not contain all of the forward-looking statements made in this Annual Report on Form 10-K.

You should not rely upon forward-looking statements as predictions of future events. We have based the forward-looking statements contained in this Annual Report on Form 10-K primarily on our current expectations and projections about future events and trends that we believe may affect our business, financial condition, results of operations and prospects. The outcome of the events described in these forward-looking statements is subject to risks, uncertainties and other factors described in the section titled "Risk Factors" and elsewhere in this Annual Report on Form 10-K. Moreover, we operate in a very competitive and rapidly changing environment. New risks and uncertainties emerge from time to time and it is not possible for us to predict all risks and uncertainties that could have an impact on the forward-looking statements contained in this Annual Report on Form 10-K. We cannot assure you that the results, events and circumstances reflected in the forward-looking statements will be achieved or occur, and actual results, events or circumstances could differ materially from those described in the forward-looking statements.

The forward-looking statements made in this Annual Report on Form 10-K relate only to events as of the date on which the statements are made. We undertake no obligation to update any forward-looking statements made in this Annual Report on Form 10-K to reflect events or circumstances after the date of this Annual Report on Form 10-K or to reflect new information or the occurrence of unanticipated events, except as required by law. We may not actually achieve the plans, intentions or expectations disclosed in our forward-looking statements and you should not place undue reliance on our forward-looking statements. Our forward-looking statements do not reflect the potential impact of any future acquisitions, mergers, dispositions, joint ventures or investments we may make.

Software developers are reinventing nearly every aspect of business today. Yet as developers, we repeatedly encountered an area where we could not innovate—communications. Because communication is a fundamental human activity and vital to building great businesses, we wanted to incorporate communications into our software applications, but the barriers to innovation were too high. Twilio was started to solve this problem.

We believe the future of communications will be written in software, by the developers of the world—our customers. By empowering them, our mission is to fuel the future of communications.

Cloud platforms are a new category of software that enable developers to build and manage applications without the complexity of creating and maintaining the underlying infrastructure. These platforms have arisen to enable a fast pace of innovation across a range of categories, such as computing and storage. We are the leader in the Cloud Communications Platform category. We enable developers to build, scale and operate real-time communications within software applications.

Our developer-first platform approach consists of three things: our Programmable Communications Cloud, Super Network and Business Model for Innovators. Our Programmable Communications Cloud software enables developers to embed voice, messaging, video and authentication capabilities into their applications via our simple-to-use Application Programming Interfaces, or APIs. We do not aim to provide complete business solutions, rather our Programmable Communications Cloud offers flexible building blocks that enable our customers to build what they need. The Super Network is our software layer that allows our customers' software to communicate with connected devices globally. It interconnects with communications networks around the world and continually analyzes data to optimize the quality and cost of communications that flow through our platform. Our Business Model for Innovators empowers developers by reducing friction and upfront costs, encouraging experimentation and enabling developers to grow as customers as their ideas succeed.

We had 36,606 Active Customer Accounts as of December 31, 2016, representing organizations big and small, old and young, across nearly every industry, with one thing in common: they are competing by using the power of software to build differentiation through communications. With our platform, our customers are disrupting existing industries and creating new ones. For example, our customers have reinvented hired transportation by connecting riders and drivers, with communications as a critical part of each transaction. Our customers' software applications use our platform to notify a diner when a table is ready, a traveler when a flight is delayed or a shopper when a package has shipped. The range of applications that developers build with the Twilio platform has proven to be nearly limitless.

Our goal is for Twilio to be in the toolkit of every software developer in the world. Because big ideas often start small, we encourage developers to experiment and iterate on our platform. We love when developers explore what they can do with Twilio, because one day they may have a business problem that they will use our products to solve.

As our customers succeed, we share in their success through our usage-based revenue model. Our revenue grows as customers increase their usage of a product, extend their usage of a product to new applications or adopt a new product. We believe the most useful indicator of this increased activity from our existing customer accounts is our Dollar-Based Net Expansion Rate, which was 161% and 155% for the years ended December 31, 2016 and 2015, respectively. See the section titled "Management's Discussion and Analysis of Financial Condition and Results of Operations—Key Business Metrics—Dollar-Based Net Expansion Rate."

Twilio's mission is to fuel the future of communications. We enable developers to build, scale and operate real-time communications within software applications.

We believe every application can be enhanced through the power of communication. Over time, we believe that all of our communications that do not occur in person will be integrated into software applications. Our platform approach enables developers to build this future.

Our Programmable Communications Cloud, Super Network and Business Model for Innovators work together to create value for our customers and a competitive advantage for our company.

Our Programmable Communications Cloud provides a range of products that enables developers to embed voice, messaging, video and authentication capabilities into their applications. Our easy-to-use developer APIs provide a programmatic channel to access our software. Developers can utilize our

intuitive programming language, TwiML, to specify application functions such as <Dial>, <Record> and <Play>, leveraging our software to manage the complexity of executing the specified functions.

Our Programmable Communications Cloud consists of software products that can be used individually or in combination to build rich contextual communications within applications. We do not aim to provide complete business solutions, rather our Programmable Communications Cloud offers flexible building blocks that enable our customers to build what they need. Our Programmable Communications Cloud includes:

Using our software, developers, including our Solution Partner customers, are able to incorporate communications into applications that span a range of industries and functionalities.

Our developers continually impress us with what they are able to build using our platform. In addition to our common use cases, we have a number of uncommon use cases that demonstrate the versatility of our platform and the creativity of our developer community.

Our Programmable Communications Cloud is built on top of our global software layer, which we call our Super Network. Our Super Network interfaces intelligently with communications networks globally. We do not own any physical network infrastructure. We use software to build a high performance network that optimizes performance for our customers. Our Super Network breaks down the geopolitical boundaries and scale limitations of the physical network infrastructure.

Our platform has global reach, consisting of 26 cloud data centers in eight regions. We interconnect those cloud data centers with network service providers around the world, giving us redundant means to reach users globally. These distributed data centers also allow our software to run in close proximity to end users and network service providers to minimize latency. Our Super Network interconnects with network service providers around the world, including carriers, mobile network operators and real-time data information service providers. When our customers use our products, the communications are transmitted through one or more of the network service providers that are connected to our Super Network. Our proprietary technology selects which network service providers to use and routes the communications in order to optimize the quality and cost of the communications across our product offerings. In addition, a very small number of customers have chosen to use certain Programmable Voice products to build one or more applications that augment their existing communications infrastructure and operate through their own network service providers. We are continually adding new network service provider relationships as we scale, and we are not dependent upon any single network service provider to conduct our business. We are continually adding new network service provider relationships as we scale.

Our Super Network analyzes massive volumes of data from end users, their applications and the communications networks to optimize our customers' communications for quality and cost. With every new message and call, our Super Network becomes more robust, intelligent and efficient, enabling us to provide better performance at lower prices to our customers. Our Super Network's sophistication becomes increasingly difficult for others to replicate over time.

Our goal is to include Twilio in the toolkit of every developer in the world. Because big ideas often start small, developers need the freedom and tools to experiment and iterate on their ideas.

In order to empower developers to experiment, our developer-first business model is low friction, eliminating the upfront costs, time and complexity that typically hinder innovation. Developers can begin building with a free trial. They have access to self-service documentation and free customer support to guide them through the process. Once developers determine that our software meets their needs, they can flexibly increase consumption and pay based on usage. In short, we acquire developers like consumers and enable them to spend like enterprises.

We are the leader in the Cloud Communications Platform category based on revenue, market share and reputation, and intend to continue to set the pace for innovation. We will continue to invest aggressively in our platform approach, which prioritizes increasing our reach and scale. We intend to pursue the following growth strategies:

Our core values, called our "Nine Values," are at the center of everything that we do. As a company built by developers for developers, these values guide us to work in a way that exemplifies many attributes of the developer ethos. These are not mere words on the wall. We introduce these values to new hires upon joining our company, and we continually weave these values into everything we do. Our values provide a guide for the way our teams work, communicate, set goals and make decisions.

We believe leadership is a behavior, not a position. In addition to our values, we have articulated the leadership traits we all strive to achieve. Our leadership principles apply to every Twilion, not just managers or executives, and provide a personal growth path for employees in their journeys to become better leaders.

The combination of our Nine Values and our leadership principles has created a blueprint for how Twilions worldwide interact with customers and with each other, and for how they respond to new challenges and opportunities.

We believe we can create greater social good through better communications. Through Twilio.org, which is a part of our company and not a separate legal entity, we donate and discount our products to nonprofits, who use our products to engage their audience, expand their reach and focus on making a meaningful change in the world. Twilio.org's mission is to send a billion messages for good. To that end, we have reserved 780,397 shares of our Class A common stock to fund and support operations of Twilio.org, which represented 1% of our outstanding capital stock on the date it was approved by our board of directors. In our follow-on public offering, we sold 100,000 shares of Class A common stock to fund and support the operations of Twilio.org, and the number of remaining reserved shares was reduced accordingly to 680,397.

Our Programmable Communications Cloud consists of software for voice, messaging, video and authentication that empowers developers to build applications that can communicate with connected devices globally. We do not aim to provide complete business solutions, rather our Programmable Communications Cloud offers flexible building blocks that enable our customers to build what they need.

Our Programmable Voice software products allow developers to build solutions to make and receive phone calls globally, and incorporate advanced voice functionality such as text-to-speech, conferencing, recording and transcription. Programmable Voice, through our advanced call control software, allows developers to build customized applications that address use cases such as contact centers, call tracking and analytics solutions and anonymized communications. Our voice software works over both the traditional public switch telephone network, as Twilio Voice, and over Internet Protocol, as Twilio Client. Programmable Voice includes:

We charge on a per-minute or per-phone-number basis for most of our Programmable Voice products.

Our Programmable Messaging software products allow developers to build solutions to send and receive text messages globally, and incorporate advanced messaging functionality such as emoji, picture messaging and localized languages. Our customers use Programmable Messaging, through software controls, to power use cases, such as appointment reminders, delivery notifications, order confirmations and customer care. We offer messaging over long-code numbers, short-code numbers, messaging apps such as Facebook Messenger and over IP through our Android, iOS and JavaScript software development kits. Programmable Messaging includes:

We charge on a per-message or per-phone-number basis for most of our Programmable Messaging products.

Our recently introduced Programmable Video software products enable developers to build next-generation mobile and web applications with embedded video, including for use cases such as customer care, collaboration and physician consultations. Programmable Video includes:

In November 2016, we acquired the proprietary WebRTC media processing technologies built by the team behind the Kurento Open Source Project. The Kurento Media Server capabilities, including large group communications, transcoding, recording and advanced media processing, has been integrated into Twilio Programmable Video.

We charge on a per-connected-endpoint, per-active-endpoint and per-gigabit basis for our Programmable Video products.

While developers can build a broad range of applications on our platform, certain use cases are more common. Our Use Case APIs build upon the above products to offer more fully implemented functionality for a specific purpose, such as two-factor authentication, thereby saving developers significant time in building their applications. The following are common uses cases for our Use Case APIs:

Identity and communications are closely linked, and this is a critical business need for our customers. Using our two-factor authentication APIs, developers can add an extra layer of security to their applications with second-factor passwords sent to a user's phone via SMS, voice or push notifications. Our Programmable Authentication products include:

A software product that enables intelligent multi-task routing in contact centers to optimize workflows, such as routing a call to an available agent. A task can be a phone call, SMS, lead, support ticket or even machine learning from a connected device.

Launched in May 2016, our Add-on Marketplace allows third parties to integrate their capabilities directly into our Cloud Communications Platform. This capability allows us to further leverage our community to provide new and differentiated functionality for our customers, while also opening up a new market for our partners.

We share in the revenue generated by our partners for their solutions sold through our Add-on Marketplace.

As of December 31, 2016, we had a total 730 employees, including 125 employees located outside the United States. None of our employees are represented by a labor union or covered by a collective bargaining agreement. We have not experienced any work stoppages, and we consider our relations with our employees to be good.

Our research and development efforts are focused on ensuring that our platform is resilient and available to our customers at any time, and on enhancing our existing products and developing new products.

Our research and development organization is built around small development teams. Our small development teams foster greater agility, which enables us to develop new, innovative products and

make rapid changes to our infrastructure that increase resiliency and operational efficiency. Our development teams designed, built and continue to expand our Programmable Communications Cloud, which enables developers to embed voice, messaging, video and authentication capabilities into their applications. Our development teams have also designed, built and continue to expand the software infrastructure that we have deployed to create our Super Network.

As of December 31, 2016, we had 390 employees in our research and development organization. We intend to continue to invest in our research and development capabilities to extend our platform and bring the power of contextual communications to a broader range of applications, geographies and customers. Our research and development expenses for the years ended December 31, 2016, 2015 and 2014 were $77.9 million, $42.6 million and $21.8 million, respectively.

Our sales and marketing teams work together closely to drive awareness and adoption of our platform, accelerate customer acquisition and generate revenue from customers.

Our go-to-market model is primarily focused on reaching and serving the needs of developers. We are a pioneer of developer evangelism and education and have cultivated a large global developer community. We reach developers through community events and conferences, including our SIGNAL developer conference, to demonstrate how every developer can create differentiated applications incorporating communications using our products.

Once developers are introduced to our platform, we provide them with a low-friction trial experience. By accessing our easy-to-configure APIs, extensive self-service documentation and customer support team, developers can build our products into their applications and then test such applications during an initial free trial period that we provide. Once they have decided to use our products beyond the initial free trial period, customers provide their credit card information and only pay for the actual usage of our products. Our self-serve pricing matrix is publicly available and it allows for customers to receive automatic tiered discounts as their usage of our products increases. As customers' use of our products grows larger, some enter into negotiated contracts with terms that dictate pricing, and typically include some level of minimum revenue commitments. Historically, we have acquired the substantial majority of our customers through this self-service model. As customers expand their usage of our platform, our relationships with them often evolve to include business leaders within their organizations. Once our customers reach a certain spending level with us, we support them with account managers or customer success advocates to ensure their satisfaction and expand their usage of our products.

When potential customers do not have the available developer resources to build their own applications, we refer them to our Solution Partners, who embed our products in their solutions that they sell to other businesses, such as contact centers and sales force and marketing automation.

We also supplement our self-service model with a sales effort aimed at engaging larger potential customers, strategic leads and existing customers through an enterprise sales approach. We have supplemented this sales effort with a new product launch, our Twilio Enterprise Plan, which provides new capabilities for advanced security, access management and granular administration. Our sales organization targets technical leaders and business leaders who are seeking to leverage software to drive competitive differentiation. As we educate these leaders on the benefits of developing applications incorporating our products to differentiate their business, they often consult with their developers regarding implementation. We believe that developers are often advocates for our products as a result of our developer-focused approach. Our sales organization includes sales development, inside sales, field sales and sales engineering personnel.

As of December 31, 2016, we had 240 employees in our sales and marketing organization.

We have designed our products and platform to be self-service and require minimal customer support. To enable seamless self-service, we provide all of our users with helper libraries, comprehensive documentation, how-to's and tutorials. We supplement and enhance these tools with the participation of our engaged developer community. In addition, we provide support options to address the individualized needs of our customers. All developers get free email based support with API status notifications. Our developers also engage with the broader Twilio community to resolve certain issues.

We also offer three additional paid tiers of email and phone support with increasing levels of availability and guaranteed response times. Our highest tier personalized plan is intended for our largest customers and includes guaranteed response times that vary based on the priority of the request, a dedicated support engineer, a duty manager and quarterly status review. Our support model is global, with 24x7 coverage and support offices located in the United States, the United Kingdom, Estonia and Singapore. We currently derive an insignificant amount of revenue from fees charged for customer support.

The market for Cloud Communications Platform is rapidly evolving and increasingly competitive. We believe that the principal competitive factors in our market are:

We believe that we compete favorably on the basis of the factors listed above. We believe that none of our competitors currently compete directly with us across all of our product offerings.

Some of our competitors have greater financial, technical and other resources, greater name recognition, larger sales and marketing budgets and larger intellectual property portfolios. As a result, certain of our competitors may be able to respond more quickly and effectively than we can to new or changing opportunities, technologies, standards or customer requirements. In addition, some competitors may offer products or services that address one or a limited number of functions at lower

prices, with greater depth than our products or geographies where we do not operate. With the introduction of new products and services and new market entrants, we expect competition to intensify in the future. Moreover, as we expand the scope of our platform, we may face additional competition.

We rely on a combination of patent, copyright, trademark and trade secret laws in the United States and other jurisdictions, as well as license agreements and other contractual protections, to protect our proprietary technology. We also rely on a number of registered and unregistered trademarks to protect our brand.

As of December 31, 2016, in the United States, we had been issued 58 patents, which expire between 2029 and 2036, and had 43 patent applications pending for examination and four pending provisional applications. As of such date, we also had six issued patents and eight patent applications pending for examination in foreign jurisdictions, all of which are related to U.S. patents and patent applications. In addition, as of December 31, 2016, we had 13 trademarks registered in the United States and 35 trademarks registered in foreign jurisdictions.

In addition, we seek to protect our intellectual property rights by implementing a policy that requires our employees and independent contractors involved in development of intellectual property on our behalf to enter into agreements acknowledging that all works or other intellectual property generated or conceived by them on our behalf are our property, and assigning to us any rights, including intellectual property rights, that they may claim or otherwise have in those works or property, to the extent allowable under applicable law.

Despite our efforts to protect our technology and proprietary rights through intellectual property rights, licenses and other contractual protections, unauthorized parties may still copy or otherwise obtain and use our software and other technology. In addition, we intend to continue to expand our international operations, and effective intellectual property, copyright, trademark and trade secret protection may not be available or may be limited in foreign countries. Any significant impairment of our intellectual property rights could harm our business or our ability to compete. Further, companies in the communications and technology industries may own large numbers of patents, copyrights and trademarks and may frequently threaten litigation, or file suit against us based on allegations of infringement or other violations of intellectual property rights. We are currently subject to, and expect to face in the future, allegations that we have infringed the intellectual property rights of third parties, including our competitors and non-practicing entities.

We are subject to a number of U.S. federal and state and foreign laws and regulations that involve matters central to our business. These laws and regulations may involve privacy, data protection, intellectual property, competition, consumer protection, export taxation or other subjects. Many of the laws and regulations to which we are subject are still evolving and being tested in courts and could be interpreted in ways that could harm our business. In addition, the application and interpretation of these laws and regulations often are uncertain, particularly in the new and rapidly evolving industry in which we operate. Because global laws and regulations have continued to develop and evolve rapidly, it is possible that we may not be, or may not have been, compliant with each such applicable law or regulation.

The Telephone Consumer Protection Act of 1991, or TCPA, restricts telemarketing and the use of automatic text messages without proper consent. The scope and interpretation of the laws that are or may be applicable to the delivery of text messages are continuously evolving and developing. If we do not comply with these laws or regulations or if we become liable under these laws or regulations due to

the failure of our customers to comply with these laws by obtaining proper consent, we could face direct liability.

Twilio Inc. was incorporated in Delaware in March 2008. Our principal executive offices are located at 375 Beale Street, Third Floor, San Francisco, California 94105, and our telephone number is (415) 390-2337. Our website address is www.twilio.com. Information contained on, or that can be accessed through, our website does not constitute part of this Annual Report on Form 10-K.

Information about geographic revenue is set forth in Note 9 of our Notes to our Consolidated Financial Statements included in Part II, Item 8, "Financial Statements and Supplementary Data" of this Annual Report on Form 10-K.

The following filings are available through our investor relations website after we file them with the Securities and Exchange Commission ("SEC"): Annual Report on Form 10-K, Quarterly Reports on Form 10-Q and our Proxy Statement for our annual meeting of stockholders. These filings are also available for download free of charge on our investor relations website. Our investor relations website is located at http://investors.twilio.com/. You may obtain copies of this information by mail from the Public Reference Section of the SEC, 100 F Street, N.E., Room 1580, Washington, D.C. 20549. The SEC also maintains an Internet website that contains reports, proxy statements and other information about issuers, like us, that file electronically with the SEC. The address of that website is www.sec.gov.

We webcast our earnings calls and certain events we participate in or host with members of the investment community on our investor relations website. Additionally, we provide notifications of news or announcements regarding our financial performance, including SEC filings, investor events, press and earnings releases, and blogs as part of our investor relations website. Further corporate governance information, including our corporate governance guidelines and code of business conduct and ethics, is also available on our investor relations website under the heading "Corporate Governance." The contents of our websites are not intended to be incorporated by reference into this Annual Report on Form 10-K or in any other report or document we file with the SEC, and any references to our websites are intended to be inactive textual references only.

A description of the risks and uncertainties associated with our business is set forth below. You should carefully consider the risks and uncertainties described below, together with all of the other information in this Annual Report on Form 10-K, including the section titled "Management's Discussion and Analysis of Financial Condition and Results of Operations" and our condensed consolidated financial statements and related notes appearing elsewhere in this Annual Report on Form 10-K. The risks and uncertainties described below may not be the only ones we face. If any of the risks actually occur, our business, financial condition, results of operations and prospects could be materially and adversely affected. In that event, the market price of our Class A common stock could decline.

The market for our products and platform is new and unproven, may decline or experience limited growth and is dependent in part on developers continuing to adopt our platform and use our products.

We were founded in 2008, and have been developing and providing a cloud-based platform that enables developers and organizations to integrate voice, messaging and video communications capabilities into their software applications. This market is relatively new and unproven and is subject to a number of risks and uncertainties. We believe that our revenue currently constitutes a significant portion of the total revenue in this market, and therefore, we believe that our future success will depend in large part on the growth, if any, of this market. The utilization of APIs by developers and organizations to build communications functionality into their applications is still relatively new, and developers and organizations may not recognize the need for, or benefits of, our products and platform. Moreover, if they do not recognize the need for and benefits of our products and platform, they may decide to adopt alternative products and services to satisfy some portion of their business needs. In order to grow our business and extend our market position, we intend to focus on educating developers and other potential customers about the benefits of our products and platform, expanding the functionality of our products and bringing new technologies to market to increase market acceptance and use of our platform. Our ability to expand the market that our products and platform address depends upon a number of factors, including the cost, performance and perceived value associated with such products and platform. The market for our products and platform could fail to grow significantly or there could be a reduction in demand for our products as a result of a lack of developer acceptance, technological challenges, competing products and services, decreases in spending by current and prospective customers, weakening economic conditions and other causes. If our market does not experience significant growth or demand for our products decreases, then our business, results of operations and financial condition could be adversely affected.

We have a history of losses and we are uncertain about our future profitability.

We have incurred net losses in each year since our inception, including net losses of $41.3 million, $35.5 million and $26.8 million in 2016, 2015 and 2014, respectively. We had an accumulated deficit of $186.7 million as of December 31, 2016. We expect to continue to expend substantial financial and other resources on, among other things:

These investments may not result in increased revenue or growth of our business. We also expect that our revenue growth rate will decline over time. Accordingly, we may not be able to generate sufficient revenue to offset our expected cost increases and achieve and sustain profitability. If we fail to achieve and sustain profitability, then our business, results of operations and financial condition would be adversely affected.

We have experienced rapid growth and expect our growth to continue, and if we fail to effectively manage our growth, then our business, results of operations and financial condition could be adversely affected.

We have experienced substantial growth in our business since inception. For example, our headcount has grown from 521 employees on December 31, 2015 to 730 employees on December 31, 2016. In addition, we are rapidly expanding our international operations. Our international headcount grew from 69 employees as of December 31, 2015 to 125 employees as of December 31, 2016, and we established operations in one new country within that same period. We expect to continue to expand our international operations in the future. We have also experienced significant growth in the number of customers, usage and amount of data that our platform and associated infrastructure support. This growth has placed and may continue to place significant demands on our corporate culture, operational infrastructure and management.

We believe that our corporate culture has been a critical component of our success. We have invested substantial time and resources in building our team and nurturing our culture. As we expand our business and mature as a public company, we may find it difficult to maintain our corporate culture while managing this growth. Any failure to manage our anticipated growth and organizational changes in a manner that preserves the key aspects of our culture could hurt our chance for future success, including our ability to recruit and retain personnel, and effectively focus on and pursue our corporate objectives. This, in turn, could adversely affect our business, results of operations and financial condition.

In addition, in order to successfully manage our rapid growth, our organizational structure has become more complex. In order to manage these increasing complexities, we will need to continue to scale and adapt our operational, financial and management controls, as well as our reporting systems and procedures. The expansion of our systems and infrastructure will require us to commit substantial financial, operational and management resources before our revenue increases and without any assurances that our revenue will increase.

Finally, continued growth could strain our ability to maintain reliable service levels for our customers. If we fail to achieve the necessary level of efficiency in our organization as we grow, then our business, results of operations and financial condition could be adversely affected.

Our quarterly results may fluctuate, and if we fail to meet securities analysts' and investors' expectations, then the trading price of our Class A common stock and the value of your investment could decline substantially.

Our results of operations, including the levels of our revenue, cost of revenue, gross margin and operating expenses, have fluctuated from quarter to quarter in the past and may continue to vary significantly in the future. These fluctuations are a result of a variety of factors, many of which are outside of our control, may be difficult to predict and may or may not fully reflect the underlying performance of our business. If our quarterly results of operations fall below the expectations of investors or securities analysts, then the trading price of our Class A common stock could decline

substantially. Some of the important factors that may cause our results of operations to fluctuate from quarter to quarter include:

The occurrence of one or more of the foregoing and other factors may cause our results of operations to vary significantly. As such, we believe that quarter-to-quarter comparisons of our results of operations may not be meaningful and should not be relied upon as an indication of future performance. In addition, a significant percentage of our operating expenses is fixed in nature and is based on forecasted revenue trends. Accordingly, in the event of a revenue shortfall, we may not be able to mitigate the negative impact on our income (loss) and margins in the short term. If we fail to meet or exceed the expectations of investors or securities analysts, then the trading price of our Class A common stock could fall substantially, and we could face costly lawsuits, including securities class action suits.

Additionally, certain large scale events, such as major elections and sporting events, can significantly impact usage levels on our platform, which could cause fluctuations in our results of operations. We expect that significantly increased usage of all communications platforms, including ours, during certain seasonal and one-time events could impact delivery and quality of our products during those events. We also experienced increased expenses in the second quarter of 2015 due to our developer conference, SIGNAL, which we again hosted in the second quarter of 2016 and plan to host annually. Such annual and one-time events may cause fluctuations in our results of operations and may impact both our revenue and operating expenses.

If we are not able to maintain and enhance our brand and increase market awareness of our company and products, then our business, results of operations and financial condition may be adversely affected.

We believe that maintaining and enhancing the "Twilio" brand identity and increasing market awareness of our company and products, particularly among developers, is critical to achieving widespread acceptance of our platform, to strengthen our relationships with our existing customers and to our ability to attract new customers. The successful promotion of our brand will depend largely on our continued marketing efforts, our ability to continue to offer high quality products, our ability to be thought leaders in the cloud communications market and our ability to successfully differentiate our products and platform from competing products and services. Our brand promotion and thought leadership activities may not be successful or yield increased revenue. In addition, independent industry analysts often provide reviews of our products and competing products and services, which may significantly influence the perception of our products in the marketplace. If these reviews are negative or not as strong as reviews of our competitors' products and services, then our brand may be harmed.

From time to time, our customers have complained about our products, such as complaints about our pricing and customer support. If we do not handle customer complaints effectively, then our brand and reputation may suffer, our customers may lose confidence in us and they may reduce or cease their use of our products. In addition, many of our customers post and discuss on social media about Internet-based products and services, including our products and platform. Our success depends, in part, on our ability to generate positive customer feedback and minimize negative feedback on social media channels where existing and potential customers seek and share information. If actions we take or changes we make to our products or platform upset these customers, then their online commentary could negatively affect our brand and reputation. Complaints or negative publicity about us, our products or our platform could materially and adversely impact our ability to attract and retain customers, our business, results of operations and financial condition.

The promotion of our brand also requires us to make substantial expenditures, and we anticipate that these expenditures will increase as our market becomes more competitive and as we expand into new markets. To the extent that these activities increase revenue, this revenue still may not be enough to offset the increased expenses we incur. If we do not successfully maintain and enhance our brand, then our business may not grow, we may see our pricing power reduced relative to competitors and we may lose customers, all of which would adversely affect our business, results of operations and financial condition.

Our business depends on customers increasing their use of our products and any loss of customers or decline in their use of our products could materially and adversely affect our business, results of operations and financial condition.

Our ability to grow and generate incremental revenue depends, in part, on our ability to maintain and grow our relationships with existing customers and to have them increase their usage of our platform. If our customers do not increase their use of our products, then our revenue may decline and our results of operations may be harmed. Customers are charged based on the usage of our products. Most of our customers do not have long-term contractual financial commitments to us and, therefore, most of our customers may reduce or cease their use of our products at any time without penalty or termination charges. We cannot accurately predict customers' usage levels and the loss of customers or reductions in their usage levels of our products may each have a negative impact on our business, results of operations and financial condition. Reductions in usage from existing customers and the loss of customers could cause our Dollar-Based Net Expansion Rate to decline in the future if customers are not satisfied with our products, the value proposition of our products or our ability to otherwise meet their needs and expectations. If a significant number of customers cease using, or reduce their usage of our products, then we may be required to spend significantly more on sales and marketing than we currently plan to spend in order to maintain or increase revenue from customers. Such additional sales and marketing expenditures could adversely affect our business, results of operations and financial condition.

If we are unable to attract new customers in a cost-effective manner, then our business, results of operations and financial condition would be adversely affected.

In order to grow our business, we must continue to attract new customers in a cost-effective manner. We use a variety of marketing channels to promote our products and platform, such as developer events and evangelism, as well as search engine marketing and optimization. We periodically adjust the mix of our other marketing programs such as regional customer events, email campaigns, billboard advertising and public relations initiatives. If the costs of the marketing channels we use increase dramatically, then we may choose to use alternative and less expensive channels, which may not be as effective as the channels we currently use. As we add to or change the mix of our marketing strategies, we may need to expand into more expensive channels than those we are currently in, which could adversely affect our business, results of operations and financial condition. We will incur marketing expenses before we are able to recognize any revenue that the marketing initiatives may generate, and these expenses may not result in increased revenue or brand awareness. We have made in the past, and may make in the future, significant expenditures and investments in new marketing campaigns, and we cannot assure you that any such investments will lead to the cost-effective acquisition of additional customers. If we are unable to maintain effective marketing programs, then our ability to attract new customers could be materially and adversely affected, our advertising and marketing expenses could increase substantially and our results of operations may suffer.

If we do not develop enhancements to our products and introduce new products that achieve market acceptance, our business, results of operations and financial condition could be adversely affected.

Our ability to attract new customers and increase revenue from existing customers depends in part on our ability to enhance and improve our existing products, increase adoption and usage of our products and introduce new products. The success of any enhancements or new products depends on several factors, including timely completion, adequate quality testing, actual performance quality, market-accepted pricing levels and overall market acceptance. Enhancements and new products that we develop may not be introduced in a timely or cost-effective manner, may contain errors or defects, may have interoperability difficulties with our platform or other products or may not achieve the broad market acceptance necessary to generate significant revenue. Furthermore, our ability to increase the

usage of our products depends, in part, on the development of new use cases for our products, which is typically driven by our developer community and may be outside of our control. We also have invested, and may continue to invest, in the acquisition of complementary businesses, technologies, services, products and other assets that expand the products that we can offer our customers. We may make these investments without being certain that they will result in products or enhancements that will be accepted by existing or prospective customers. Our ability to generate usage of additional products by our customers may also require increasingly sophisticated and more costly sales efforts and result in a longer sales cycle. If we are unable to successfully enhance our existing products to meet evolving customer requirements, increase adoption and usage of our products, develop new products, or if our efforts to increase the usage of our products are more expensive than we expect, then our business, results of operations and financial condition would be adversely affected.

If we are unable to increase adoption of our products by enterprises, our business, results of operations and financial condition may be adversely affected.

Historically, we have relied on the adoption of our products by software developers through our self-service model for a significant majority of our revenue, and we currently generate only a small portion of our revenue from enterprise customers. Our ability to increase our customer base, especially among enterprises, and achieve broader market acceptance of our products will depend, in part, on our ability to effectively organize, focus and train our sales and marketing personnel. We have limited experience selling to enterprises and only recently established an enterprise-focused sales force.

Our ability to convince enterprises to adopt our products will depend, in part, on our ability to attract and retain sales personnel with experience selling to enterprises. We believe that there is significant competition for experienced sales professionals with the skills and technical knowledge that we require. Our ability to achieve significant revenue growth in the future will depend, in part, on our ability to recruit, train and retain a sufficient number of experienced sales professionals, particularly those with experience selling to enterprises. In addition, even if we are successful in hiring qualified sales personnel, new hires require significant training and experience before they achieve full productivity, particularly for sales efforts targeted at enterprises and new territories. Our recent hires and planned hires may not become as productive as quickly as we expect and we may be unable to hire or retain sufficient numbers of qualified individuals in the future in the markets where we do business. Because we do not have a long history of targeting our sales efforts at enterprises, we cannot predict whether, or to what extent, our sales will increase as we organize and train our sales force or how long it will take for sales personnel to become productive.

As we seek to increase the adoption of our products by enterprises, we expect to incur higher costs and longer sales cycles. In this market segment, the decision to adopt our products may require the approval of multiple technical and business decision makers, including security, compliance, procurement, operations and IT. In addition, while enterprise customers may quickly deploy our products on a limited basis, before they will commit to deploying our products at scale, they often require extensive education about our products and significant customer support time, engage in protracted pricing negotiations and seek to secure readily available development resources. In addition, sales cycles for enterprises are inherently more complex and less predictable than the sales through our self-service model, and some enterprise customers may not use our products enough to generate revenue that justifies the cost to obtain such customers. In addition, these complex and resource intensive sales efforts could place additional strain on our limited product and engineering resources. Further, enterprises, including some of our customers, may choose to develop their own solutions that do not include our products. They also may demand reductions in pricing as their usage of our products increases, which could have an adverse impact on our gross margin. As a result of our limited experience selling and marketing to enterprises, our efforts to sell to these potential customers may not be successful. If we are unable to increase the revenue that we derive from enterprises, then our business, results of operations and financial condition may be adversely affected.

If we are unable to expand our relationships with existing Solution Partner customers and add new Solution Partner customers, our business, results of operations and financial condition could be adversely affected.

We believe that the continued growth of our business depends in part upon developing and expanding strategic relationships with Solution Partner customers. Solution Partner customers embed our software products in their solutions, such as software applications for contact centers and sales force and marketing automation, and then sell such solutions to other businesses. When potential customers do not have the available developer resources to build their own applications, we refer them to our network of Solution Partner customers.

As part of our growth strategy, we intend to expand our relationships with existing Solution Partner customers and add new Solution Partner customers. If we fail to expand our relationships with existing Solution Partner customers or establish relationships with new Solution Partner customers, in a timely and cost-effective manner, or at all, then our business, results of operations and financial condition could be adversely affected. Additionally, even if we are successful at building these relationships but there are problems or issues with integrating our products into the solutions of these customers, our reputation and ability to grow our business may be harmed.

We rely upon Amazon Web Services to operate our platform and any disruption of or interference with our use of Amazon Web Services would adversely affect our business, results of operations and financial condition.

We outsource substantially all of our cloud infrastructure to Amazon Web Services, or AWS, which hosts our products and platform. Customers of our products need to be able to access our platform at any time, without interruption or degradation of performance. AWS runs its own platform that we access, and we are, therefore, vulnerable to service interruptions at AWS. We have experienced, and expect that in the future we may experience interruptions, delays and outages in service and availability from time to time due to a variety of factors, including infrastructure changes, human or software errors, website hosting disruptions and capacity constraints. Capacity constraints could be due to a number of potential causes including technical failures, natural disasters, fraud or security attacks. For instance, in September 2015, AWS suffered a significant outage that had a widespread impact on the ability of our customers to use several of our products. In addition, if our security, or that of AWS, is compromised, our products or platform are unavailable or our users are unable to use our products within a reasonable amount of time or at all, then our business, results of operations and financial condition could be adversely affected. In some instances, we may not be able to identify the cause or causes of these performance problems within a period of time acceptable to our customers. It may become increasingly difficult to maintain and improve our platform performance, especially during peak usage times, as our products become more complex and the usage of our products increases. To the extent that we do not effectively address capacity constraints, either through AWS or alternative providers of cloud infrastructure, our business, results of operations and financial condition may be adversely affected. In addition, any changes in service levels from AWS may adversely affect our ability to meet our customers' requirements.

The substantial majority of the services we use from AWS are for cloud-based server capacity and, to a lesser extent, storage and other optimization offerings. AWS enables us to order and reserve server capacity in varying amounts and sizes distributed across multiple regions. We access AWS infrastructure through standard IP connectivity. AWS provides us with computing and storage capacity pursuant to an agreement that continues until terminated by either party. AWS may terminate the agreement by providing 30 days prior written notice, and may in some cases terminate the agreement immediately for cause upon notice. Although we expect that we could receive similar services from other third parties, if any of our arrangements with AWS are terminated, we could experience interruptions on our platform and in our ability to make our products available to customers, as well as delays and additional expenses in arranging alternative cloud infrastructure services.

Any of the above circumstances or events may harm our reputation, cause customers to stop using our products, impair our ability to increase revenue from existing customers, impair our ability to grow our customer base, subject us to financial penalties and liabilities under our service level agreements and otherwise harm our business, results of operations and financial condition.

To deliver our products, we rely on network service providers for our network service.

We currently interconnect with network service providers around the world to enable the use by our customers of our products over their networks. We expect that we will continue to rely heavily on network service providers for these services going forward. Our reliance on network service providers has reduced our operating flexibility, ability to make timely service changes and control quality of service. In addition, the fees that we are charged by network service providers may change daily or weekly, while we do not typically change our customers' pricing as rapidly. Furthermore, many of these network service providers do not have long-term committed contracts with us and may terminate their agreements with us without notice or restriction. If a significant portion of our network service providers stop providing us with access to their infrastructure, fail to provide these services to us on a cost-effective basis, cease operations, or otherwise terminate these services, the delay caused by qualifying and switching to other network service providers could be time consuming and costly and could adversely affect our business, results of operations and financial condition.

Further, if problems occur with our network service providers, it may cause errors or poor quality communications with our products, and we could encounter difficulty identifying the source of the problem. The occurrence of errors or poor quality communications on our products, whether caused by our platform or a network service provider, may result in the loss of our existing customers or the delay of adoption of our products by potential customers and may adversely affect our business, results of operations and financial condition.

Our future success depends in part on our ability to drive the adoption of our products by international customers.

In 2016, 2015 and 2014, we derived 16%, 14% and 12% of our revenue, respectively, from customer accounts located outside the United States. The future success of our business will depend, in part, on our ability to expand our customer base worldwide. While we have been rapidly expanding our sales efforts internationally, our experience in selling our products outside of the United States is limited. Furthermore, our developer-first business model may not be successful or have the same traction outside the United States. As a result, our investment in marketing our products to these potential customers may not be successful. If we are unable to increase the revenue that we derive from international customers, then our business, results of operations and financial condition may be adversely affected.

We are in the process of expanding our international operations, which exposes us to significant risks.

We are continuing to expand our international operations to increase our revenue from customers outside of the United States as part of our growth strategy. Between December 31, 2015 and December 31, 2016, our international headcount grew from 69 employees to 125 employees, and we opened one new office outside of the United States. We expect, in the future, to open additional foreign offices and hire employees to work at these offices in order to reach new customers and gain access to additional technical talent. Operating in international markets requires significant resources and management attention and will subject us to regulatory, economic and political risks in addition to those we already face in the United States. Because of our limited experience with international operations as well as developing and managing sales in international markets, our international expansion efforts may not be successful.

In addition, we will face risks in doing business internationally that could adversely affect our business, including:

Also, due to costs from our international expansion efforts and network service provider fees outside of the United States that are generally higher than domestic rates, our gross margin for international customers is typically lower than our gross margin for domestic customers. As a result,

our gross margin may be impacted and fluctuate as we expand our operations and customer base worldwide.

Our failure to manage any of these risks successfully could harm our international operations, and adversely affect our business, results of operations and financial condition.

We currently generate significant revenue from our largest customers, and the loss or decline in revenue from any of these customers could harm our business, results of operations and financial condition.

In 2016, 2015 and 2014, our 10 largest Active Customer Accounts generated an aggregate of 30%, 32% and 28% of our revenue, respectively. In addition, a significant portion of our revenue comes from two customers, one of which is a Variable Customer Account.

In 2016, 2015 and 2014, WhatsApp, a Variable Customer Account, accounted for 9%, 17% and 13% of our revenue, respectively. WhatsApp uses our Programmable Voice products and Programmable Messaging products in its applications to verify new and existing users on its service. Our Variable Customer Accounts, including WhatsApp, do not have long-term contracts with us and may reduce or fully terminate their usage of our products at any time without notice, penalty or termination charges. In addition, the usage of our products by WhatsApp and other Variable Customer Accounts may change significantly between periods.

A second customer, Uber, a Base Customer Account, accounted for more than 10% of our revenue in 2016, and accounted for less than 10% of our revenue in each of 2015 and 2014. Uber uses our Programmable Messaging products and Programmable Voice products. Although Uber has entered into a minimum commitment contract with us, its usage historically has significantly exceeded the minimum revenue commitment in its contract, and it could significantly reduce its usage of our products without notice or penalty.

In the event that our large customers do not continue to use our products, use fewer of our products, or use our products in a more limited capacity, or not at all, our business, results of operations and financial condition could be adversely affected.

The market in which we participate is intensely competitive, and if we do not compete effectively, our business, results of operations and financial condition could be harmed.

The market for cloud communications is rapidly evolving, significantly fragmented and highly competitive, with relatively low barriers to entry in some segments. The principal competitive factors in our market include completeness of offering, credibility with developers, global reach, ease of integration and programmability, product features, platform scalability, reliability, security and performance, brand awareness and reputation, the strength of sales and marketing efforts, customer support, as well as the cost of deploying and using our products. Our competitors fall into four primary categories:

Some of our competitors and potential competitors are larger and have greater name recognition, longer operating histories, more established customer relationships, larger budgets and significantly greater resources than we do. In addition, they have the operating flexibility to bundle competing products and services at little or no perceived incremental cost, including offering them at a lower price

as part of a larger sales transaction. As a result, our competitors may be able to respond more quickly and effectively than we can to new or changing opportunities, technologies, standards or customer requirements. In addition, some competitors may offer products or services that address one or a limited number of functions at lower prices, with greater depth than our products or in different geographies. Our current and potential competitors may develop and market new products and services with comparable functionality to our products, and this could lead to us having to decrease prices in order to remain competitive. Customers utilize our products in many ways, and use varying levels of functionality that our products offer or are capable of supporting or enabling within their applications. Customers that use many of the features of our products or use our products to support or enable core functionality for their applications may have difficulty or find it impractical to replace our products with a competitor's products or services, while customers that use only limited functionality may be able to more easily replace our products with competitive offerings.

With the introduction of new products and services and new market entrants, we expect competition to intensify in the future. In addition, some of our customers may choose to use our products and our competitors' products at the same time. Further, customers and consumers may choose to adopt other forms of electronic communications or alternative communication platforms.

Moreover, as we expand the scope of our products, we may face additional competition. If one or more of our competitors were to merge or partner with another of our competitors, the change in the competitive landscape could also adversely affect our ability to compete effectively. In addition, some of our competitors have lower list prices than us, which may be attractive to certain customers even if those products have different or lesser functionality. If we are unable to maintain our current pricing due to the competitive pressures, our margins will be reduced and our business, results of operations and financial condition would be adversely affected. In addition, pricing pressures and increased competition generally could result in reduced revenue, reduced margins, increased losses or the failure of our products to achieve or maintain widespread market acceptance, any of which could harm our business, results of operations and financial condition.

We have a limited operating history, which makes it difficult to evaluate our current business and future prospects and increases the risk of your investment.

We were founded and launched our first product in 2008. As a result of our limited operating history, our ability to forecast our future results of operations is limited and subject to a number of uncertainties, including our ability to plan for future growth. Our historical revenue growth should not be considered indicative of our future performance. We have encountered and will encounter risks and uncertainties frequently experienced by growing companies in rapidly changing industries, such as:

If we do not address these risks successfully, our business, results of operations and financial condition could be adversely affected.

We have limited experience with respect to determining the optimal prices for our products.

We charge our customers based on their use of our products. We expect that we may need to change our pricing from time to time. In the past we have sometimes reduced our prices either for individual customers in connection with long-term agreements or for a particular product. One of the challenges to our pricing is that the fees that we pay to network service providers over whose networks we transmit communications can vary daily or weekly and are affected by volume and other factors which may be outside of our control and difficult to predict. This can result in our incurring increased costs which we may be unable or unwilling to pass through to our customers, which could adversely impact our business, results of operations and financial condition.

Further, as competitors introduce new products or services that compete with ours or reduce their prices, we may be unable to attract new customers or retain existing customers based on our historical pricing. As we expand internationally, we also must determine the appropriate price to enable us to compete effectively internationally. Moreover, enterprises, which are a primary focus for our direct sales efforts, may demand substantial price concessions. In addition, if the mix of products sold changes, including for a shift to IP-based products, then we may need to, or choose to, revise our pricing. As a result, in the future we may be required or choose to reduce our prices or change our pricing model, which could adversely affect our business, results of operations and financial condition.

We typically provide monthly uptime service level commitments of up to 99.95% under our agreements with customers. If we fail to meet these contractual commitments, then our business, results of operations and financial condition could be adversely affected.

Our agreements with customers typically provide for service level commitments. If we suffer extended periods of downtime for our products or platform and we are unable to meet these commitments, then we are contractually obligated to provide a service credit, which is typically 10% of the customer's amounts due for the month in question. In addition, the performance and availability of AWS, which provides our cloud infrastructure is outside our control and, therefore, we are not in full control of whether we meet the service level commitments. As a result, our business, results of operations and financial condition could be adversely affected if we suffer unscheduled downtime that exceeds the service level commitments we have made to our customers. Any extended service outages could adversely affect our business and reputation.

Breaches of our networks or systems, or those of AWS or our network service providers, could degrade our ability to conduct our business, compromise the integrity of our products and platform, result in significant data losses and the theft of our intellectual property, damage our reputation, expose us to liability to third parties and require us to incur significant additional costs to maintain the security of our networks and data.

We depend upon our IT systems to conduct virtually all of our business operations, ranging from our internal operations and research and development activities to our marketing and sales efforts and communications with our customers and business partners. Individuals or entities may attempt to penetrate our network security, or that of our platform, and to cause harm to our business operations, including by misappropriating our proprietary information or that of our customers, employees and business partners or to cause interruptions of our products and platform. Because the techniques used by such individuals or entities to access, disrupt or sabotage devices, systems and networks change frequently and may not be recognized until launched against a target, we may be unable to anticipate these techniques, and we may not become aware in a timely manner of such a security breach which could exacerbate any damage we experience. Additionally, we depend upon our employees and contractors to appropriately handle confidential and sensitive data, including customer data, and to deploy our IT resources in safe and secure manner that does not expose our network systems to security breaches or the loss of data. Any data security incidents, including internal malfeasance by our employees, unauthorized access or usage, virus or similar breach or disruption of us or our services

providers, such as AWS or network service providers, could result in loss of confidential information, damage to our reputation, loss of customers, litigation, regulatory investigations, fines, penalties and other liabilities. Accordingly, if our cybersecurity measures and those of AWS and our network service providers, fail to protect against unauthorized access, attacks (which may include sophisticated cyberattacks) and the mishandling of data by our employees and contractors, then our reputation, business, results of operations and financial condition could be adversely affected.

Defects or errors in our products could diminish demand for our products, harm our business and results of operations and subject us to liability.

Our customers use our products for important aspects of their businesses, and any errors, defects or disruptions to our products and any other performance problems with our products could damage our customers' businesses and, in turn, hurt our brand and reputation. We provide regular updates to our products, which have in the past contained, and may in the future contain, undetected errors, failures, vulnerabilities and bugs when first introduced or released. Real or perceived errors, failures or bugs in our products could result in negative publicity, loss of or delay in market acceptance of our platform, loss of competitive position, lower customer retention or claims by customers for losses sustained by them. In such an event, we may be required, or may choose, for customer relations or other reasons, to expend additional resources in order to help correct the problem. In addition, we may not carry insurance sufficient to compensate us for any losses that may result from claims arising from defects or disruptions in our products. As a result, our reputation and our brand could be harmed, and our business, results of operations and financial condition may be adversely affected.

If we fail to adapt and respond effectively to rapidly changing technology, evolving industry standards, changing regulations, and changing customer needs, requirements or preferences, our products may become less competitive.

The market for communications in general, and cloud communications in particular, is subject to rapid technological change, evolving industry standards, changing regulations, as well as changing customer needs, requirements and preferences. The success of our business will depend, in part, on our ability to adapt and respond effectively to these changes on a timely basis. If we are unable to develop new products that satisfy our customers and provide enhancements and new features for our existing products that keep pace with rapid technological and industry change, our business, results of operations and financial condition could be adversely affected. If new technologies emerge that are able to deliver competitive products and services at lower prices, more efficiently, more conveniently or more securely, such technologies could adversely impact our ability to compete effectively.

Our platform must also integrate with a variety of network, hardware, mobile and software platforms and technologies, and we need to continuously modify and enhance our products and platform to adapt to changes and innovation in these technologies. If customers adopt new software platforms or infrastructure, we may be required to develop new versions of our products to work with those new platforms or infrastructure. This development effort may require significant resources, which would adversely affect our business, results of operations and financial condition. Any failure of our products and platform to operate effectively with evolving or new platforms and technologies could reduce the demand for our products. If we are unable to respond to these changes in a cost-effective manner, our products may become less marketable and less competitive or obsolete, and our business, results of operations and financial condition could be adversely affected.

Our reliance on SaaS technologies from third parties may adversely affect our business, results of operations and financial condition.

We rely heavily on hosted SaaS technologies from third parties in order to operate critical internal functions of our business, including enterprise resource planning, customer support and customer

relations management services. If these services become unavailable due to extended outages or interruptions, or because they are no longer available on commercially reasonable terms or prices, our expenses could increase. As a result, our ability to manage our operations could be interrupted and our processes for managing our sales process and supporting our customers could be impaired until equivalent services, if available, are identified, obtained and implemented, all of which could adversely affect our business, results of operations and financial condition.

If we are unable to develop and maintain successful relationships with independent software vendors and system integrators, our business, results of operations and financial condition could be adversely affected.

We believe that continued growth of our business depends in part upon identifying, developing and maintaining strategic relationships with independent software vendor (ISV) development platforms and system integrators. As part of our growth strategy, we plan to further develop product partnerships with ISV development platforms to embed our products as additional distribution channels and also intend to further develop partnerships and specific solution areas with systems integrators. If we fail to establish these relationships, in a timely and cost-effective manner, or at all, then our business, results of operations and financial condition could be adversely affected. Additionally, even if we are successful at developing these relationships but there are problems or issues with the integrations or enterprises are not willing to purchase through ISV development platforms, our reputation and ability to grow our business may also be adversely affected.

Any failure to offer high-quality customer support may adversely affect our relationships with our customers and prospective customers, and adversely affect our business, results of operations and financial condition.

Many of our customers depend on our customer support team to assist them in deploying our products effectively to help them to resolve post-deployment issues quickly and to provide ongoing support. If we do not devote sufficient resources or are otherwise unsuccessful in assisting our customers effectively, it could adversely affect our ability to retain existing customers and could prevent prospective customers from adopting our products. We may be unable to respond quickly enough to accommodate short-term increases in demand for customer support. We also may be unable to modify the nature, scope and delivery of our customer support to compete with changes in the support services provided by our competitors. Increased demand for customer support, without corresponding revenue, could increase costs and adversely affect our business, results of operations and financial condition. Our sales are highly dependent on our business reputation and on positive recommendations from developers. Any failure to maintain high-quality customer support, or a market perception that we do not maintain high-quality customer support, could adversely affect our reputation, business, results of operations and financial condition.

We have been sued, and may, in the future, be sued by third parties for alleged infringement of their proprietary rights, which could adversely affect our business, results of operations and financial condition.

There is considerable patent and other intellectual property development activity in our industry. Our future success depends, in part, on not infringing the intellectual property rights of others. Our competitors or other third parties have claimed and may, in the future, claim that we are infringing upon their intellectual property rights, and we may be found to be infringing upon such rights. For example, on April 30, 2015, Telesign Corporation, or Telesign, filed a lawsuit against us in the United States District Court, Central District of California (Telesign I). Telesign alleges that we are infringing three U.S. patents that it holds: U.S. Patent No. 8,462,920 ("'920"), U.S. Patent No. 8,687,038 ("'038") and U.S. Patent No. 7,945,034 ("'034"). The patent infringement allegations in the lawsuit relate to our Programmable Authentication products, our two-factor authentication use case and an API tool to find information about a phone number. Subsequently, on March 28, 2016, Telesign filed a second lawsuit against us in the United States District Court, Central District of California (Telesign II), alleging infringement of U.S. Patent No. 9,300,792 ("'792") held by Telesign. The '792 patent is in the same

patent family as the '920 and '038 patents asserted in Telesign I, and the infringement allegations in Telesign II relate to our Programmable Authentication products and our two-factor authentication use case. With respect to each of the patents asserted in Telesign I and Telesign II, the complaints seek, among other things, to enjoin us from allegedly infringing these patents along with damages for lost profits. See the section titled "Item 3. Legal Proceedings." We intend to vigorously defend these lawsuits and believe we have meritorious defenses to each. However, litigation is inherently uncertain, and any judgment or injunctive relief entered against us or any adverse settlement could negatively affect our business, results of operations and financial condition. In addition, litigation can involve significant management time and attention and be expensive, regardless of outcome. During the course of these lawsuits, there may be announcements of the results of hearings and motions and other interim developments related to the litigation. If securities analysts or investors regard these announcements as negative, the trading price of our Class A common stock may decline.

In the future, we may receive claims from third parties, including our competitors, that our products or platform and underlying technology infringe or violate a third party's intellectual property rights, and we may be found to be infringing upon such rights. We may be unaware of the intellectual property rights of others that may cover some or all of our technology. Any claims or litigation could cause us to incur significant expenses and, if successfully asserted against us, could require that we pay substantial damages or ongoing royalty payments, prevent us from offering our products, or require that we comply with other unfavorable terms. We may also be obligated to indemnify our customers or business partners in connection with any such litigation and to obtain licenses or modify our products or platform, which could further exhaust our resources. Even if we were to prevail in the event of claims or litigation against us, any claim or litigation regarding intellectual property could be costly and time-consuming and divert the attention of our management and other employees from our business. Patent infringement, trademark infringement, trade secret misappropriation and other intellectual property claims and proceedings brought against us, whether successful or not, could harm to our brand, business, results of operations and financial condition.

Indemnity provisions in various agreements potentially expose us to substantial liability for intellectual property infringement and other losses.

Our agreements with customers and other third parties typically include indemnification or other provisions under which we agree to indemnify or otherwise be liable to them for losses suffered or incurred as a result of claims of intellectual property infringement, damages caused by us to property or persons or other liabilities relating to or arising from our products or platform or other acts or omissions. The term of these contractual provisions often survives termination or expiration of the applicable agreement. Large indemnity payments or damage claims from contractual breach could harm our business, results of operations and financial condition. Although we normally contractually limit our liability with respect to such obligations, we may still incur substantial liability related to them. Any dispute with a customer with respect to such obligations could have adverse effects on our relationship with that customer and other current and prospective customers, reduce demand for our products and adversely affect our business, results of operations and financial condition.

We could incur substantial costs in protecting or defending our intellectual property rights, and any failure to protect our intellectual property could adversely affect our business, results of operations and financial condition.

Our success depends, in part, on our ability to protect our brand and the proprietary methods and technologies that we develop under patent and other intellectual property laws of the United States and foreign jurisdictions so that we can prevent others from using our inventions and proprietary information. As of December 31, 2016, we had 13 registered trademarks in the United States and 35 registered trademarks in foreign jurisdictions. In addition, as of December 31, 2016, in the United States, we had been issued 58 patents, which expire between 2029 and 2036, and had 43 patent

applications pending for examination and four pending provisional applications. As of such date, we also had six issued patents and eight patent applications pending for examination in foreign jurisdictions, all of which are related to U.S. patents and patent applications. There can be no assurance that additional patents will be issued or that any patents that have been issued or that may be issued in the future will provide significant protection for our intellectual property. If we fail to protect our intellectual property rights adequately, our competitors might gain access to our technology and our business, results of operations and financial condition may be adversely affected.

There can be no assurance that the particular forms of intellectual property protection that we seek, including business decisions about when to file trademark applications and patent applications, will be adequate to protect our business. We could be required to spend significant resources to monitor and protect our intellectual property rights. Litigation may be necessary in the future to enforce our intellectual property rights, determine the validity and scope of our proprietary rights or those of others, or defend against claims of infringement or invalidity. Such litigation could be costly, time-consuming and distracting to management, result in a diversion of significant resources, the narrowing or invalidation of portions of our intellectual property and have an adverse effect on our business, results of operations and financial condition. Our efforts to enforce our intellectual property rights may be met with defenses, counterclaims and countersuits attacking the validity and enforceability of our intellectual property rights or alleging that we infringe the counterclaimant's own intellectual property. Any of our patents, copyrights, trademarks or other intellectual property rights could be challenged by others or invalidated through administrative process or litigation.

We also rely, in part, on confidentiality agreements with our business partners, employees, consultants, advisors, customers and others in our efforts to protect our proprietary technology, processes and methods. These agreements may not effectively prevent disclosure of our confidential information, and it may be possible for unauthorized parties to copy our software or other proprietary technology or information, or to develop similar software independently without our having an adequate remedy for unauthorized use or disclosure of our confidential information. In addition, others may independently discover our trade secrets and proprietary information, and in these cases we would not be able to assert any trade secret rights against those parties. Costly and time-consuming litigation could be necessary to enforce and determine the scope of our proprietary rights, and failure to obtain or maintain trade secret protection could adversely affect our competitive business position.

In addition, the laws of some countries do not protect intellectual property and other proprietary rights to the same extent as the laws of the United States. To the extent we expand our international activities, our exposure to unauthorized copying, transfer and use of our proprietary technology or information may increase.

We cannot be certain that our means of protecting our intellectual property and proprietary rights will be adequate or that our competitors will not independently develop similar technology. If we fail to meaningfully protect our intellectual property and proprietary rights, our business, results of operations and financial condition could be adversely affected.

Our use of open source software could negatively affect our ability to sell our products and subject us to possible litigation.

Our products and platform incorporate open source software, and we expect to continue to incorporate open source software in our products and platform in the future. Few of the licenses applicable to open source software have been interpreted by courts, and there is a risk that these licenses could be construed in a manner that could impose unanticipated conditions or restrictions on our ability to commercialize our products and platform. Moreover, although we have implemented policies to regulate the use and incorporation of open source software into our products and platform, we cannot be certain that we have not incorporated open source software in our products or platform in a manner that is inconsistent with such policies. If we fail to comply with open source licenses, we

may be subject to certain requirements, including requirements that we offer our products that incorporate the open source software for no cost, that we make available source code for modifications or derivative works we create based upon, incorporating or using the open source software and that we license such modifications or derivative works under the terms of applicable open source licenses. If an author or other third party that distributes such open source software were to allege that we had not complied with the conditions of one or more of these licenses, we could be required to incur significant legal expenses defending against such allegations and could be subject to significant damages, enjoined from generating revenue from customers using products that contained the open source software and required to comply with onerous conditions or restrictions on these products. In any of these events, we and our customers could be required to seek licenses from third parties in order to continue offering our products and platform and to re-engineer our products or platform or discontinue offering our products to customers in the event re-engineering cannot be accomplished on a timely basis. Any of the foregoing could require us to devote additional research and development resources to re-engineer our products or platform, could result in customer dissatisfaction and may adversely affect our business, results of operations and financial condition.

We may acquire or invest in companies, which may divert our management's attention and result in debt or dilution to our stockholders. We may be unable to integrate acquired businesses and technologies successfully or achieve the expected benefits of such acquisitions.

We may evaluate and consider potential strategic transactions, including acquisitions of, or investments in, businesses, technologies, services, products and other assets in the future. We also may enter into relationships with other businesses to expand our products and platform, which could involve preferred or exclusive licenses, additional channels of distribution, discount pricing or investments in other companies.

Any acquisition, including our acquisition of Authy, of the proprietary WebRTC media processing technologies built by the team behind the Kurento Open Source Project and of Beepsend A.B., investment or business relationship may result in unforeseen operating difficulties and expenditures. In particular, we may encounter difficulties assimilating or integrating the businesses, technologies, products, personnel or operations of the acquired companies, particularly if the key personnel of the acquired company choose not to work for us, their products or services are not easily adapted to work with our platform, or we have difficulty retaining the customers of any acquired business due to changes in ownership, management or otherwise. Acquisitions may also disrupt our business, divert our resources and require significant management attention that would otherwise be available for development of our existing business. Moreover, the anticipated benefits of any acquisition, investment or business relationship may not be realized or we may be exposed to unknown risks or liabilities.

Negotiating these transactions can be time-consuming, difficult and expensive, and our ability to complete these transactions may often be subject to approvals that are beyond our control. Consequently, these transactions, even if announced, may not be completed. For one or more of those transactions, we may:

The occurrence of any of these foregoing could adversely affect our business, results of operations and financial condition.

We depend largely on the continued services of our senior management and other key employees, the loss of any of whom could adversely affect our business, results of operations and financial condition.

Our future performance depends on the continued services and contributions of our senior management and other key employees to execute on our business plan, to develop our products and platform, to deliver our products to customers, to attract and retain customers and to identify and pursue opportunities. The loss of services of senior management or other key employees could significantly delay or prevent the achievement of our development and strategic objectives. In particular, we depend to a considerable degree on the vision, skills, experience and effort of our co-founder and Chief Executive Officer, Jeff Lawson. None of our executive officers or other senior management personnel is bound by a written employment agreement and any of them may terminate employment with us at any time with no advance notice. The replacement of any of our senior management personnel would likely involve significant time and costs, and such loss could significantly delay or prevent the achievement of our business objectives. The loss of the services of our senior management or other key employees for any reason could adversely affect our business, results of operations and financial condition.

Most members of our management team have limited experience managing a publicly-traded company, interacting with public company investors and complying with the increasingly complex laws pertaining to public companies. Our management team may not successfully or efficiently manage us as a public company subject to significant regulatory oversight and reporting obligations under the federal securities laws and the continuous scrutiny of securities analysts and investors. These new obligations and constituents require significant attention from our senior management and could divert their attention away from the day-to-day management of our business, which could adversely affect our business, results of operations and financial condition.

If we are unable to hire, retain and motivate qualified personnel, our business will suffer.

Our future success depends, in part, on our ability to continue to attract and retain highly skilled personnel. We believe that there is, and will continue to be, intense competition for highly skilled management, technical, sales and other personnel with experience in our industry in the San Francisco Bay Area, where our headquarters are located, and in other locations where we maintain offices. We must provide competitive compensation packages and a high-quality work environment to hire, retain and motivate employees. If we are unable to retain and motivate our existing employees and attract qualified personnel to fill key positions, we may be unable to manage our business effectively, including the development, marketing and sale of our products, which could adversely affect our business, results of operations and financial condition. To the extent we hire personnel from competitors, we also may be subject to allegations that they have been improperly solicited or divulged proprietary or other confidential information.

Volatility in, or lack of performance of, our stock price may also affect our ability to attract and retain key personnel. Many of our key personnel are, or will soon be, vested in a substantial amount of shares of Class A common stock or stock options. Employees may be more likely to terminate their employment with us if the shares they own or the shares underlying their vested options have significantly appreciated in value relative to the original purchase prices of the shares or the exercise prices of the options, or, conversely, if the exercise prices of the options that they hold are significantly above the trading price of our Class A common stock. If we are unable to retain our employees, our business, results of operations and financial condition could be adversely affected.

Our products and platform and our business are subject to a variety of U.S. and international laws and regulations, including those regarding privacy, data protection and information security, and our customers may be subject to regulations related to the handling and transfer of certain types of sensitive and confidential information. Any failure of our products or products to comply with or enable our customers and channel partners to comply with applicable laws and regulations would harm our business, results of operations and financial condition.

We and our customers that use our products may be subject to privacy- and data protection-related laws and regulations that impose obligations in connection with the collection, processing and use of personal data, financial data, health data or other similar data. Existing U.S. federal and various state and foreign privacy- and data protection-related laws and regulations are evolving and subject to potentially differing interpretations, and various legislative and regulatory bodies may expand current or enact new laws and regulations regarding privacy- and data protection-related matters. New laws, amendments to or re-interpretations of existing laws and regulations, rules of self-regulatory bodies, industry standards and contractual obligations may impact our business and practices, and we may be required to expend significant resources to adapt to these changes, or stop offering our products in certain countries. These developments could adversely affect our business, results of operations and financial condition.

The U.S. federal and various state and foreign governments have adopted or proposed limitations on, or requirements regarding, the collection, distribution, use, security and storage of personally identifiable information of individuals. The U.S. Federal Trade Commission and numerous state attorneys general are applying federal and state consumer protection laws to impose standards on the online collection, use and dissemination of data, and to the security measures applied to such data. Similarly, many foreign countries and governmental bodies, including the EU member states, have laws and regulations concerning the collection and use of personally identifiable information obtained from their residents or by businesses operating within their jurisdiction, which are often more restrictive than those in the United States. Laws and regulations in these jurisdictions apply broadly to the collection, use, storage, disclosure and security of personally identifiable information that identifies or may be used to identify an individual, such as names, email addresses and, in some jurisdictions, IP addresses. Although we endeavor to have our products and platform comply with applicable laws and regulations, these and other obligations may be modified, they may be interpreted and applied in an inconsistent manner from one jurisdiction to another, and they may conflict with one another, other regulatory requirements, contractual commitments or our internal practices. In addition, we may find it necessary or desirable to join industry or other self-regulatory bodies or other privacy- or data protection-related organizations that require compliance with their rules pertaining to privacy and data protection. We also may be bound by contractual obligations relating to our collection, use and disclosure of personal, financial and other data.

We have in the past relied on adherence to the U.S. Department of Commerce's Safe Harbor Privacy Principles and compliance with the U.S.—EU and U.S.—Swiss Safe Harbor Frameworks as agreed to and set forth by the U.S. Department of Commerce, and the European Union and Switzerland. As a result of the October 6, 2015 European Union Court of Justice, or ECJ, opinion in Case C-362/14 (Schrems v. Data Protection Commissioner) regarding the adequacy of the U.S.—EU Safe Harbor Framework, the U.S.—EU Safe Harbor Framework is no longer deemed to be a valid method of compliance with restrictions set forth in the Data Protection Directive (and member states' implementations thereof) regarding the transfer of data outside of the European Economic Area. In light of the ECJ opinion, we anticipate engaging in efforts to legitimize data transfers from the European Economic Area. We may be unsuccessful in establishing legitimate means of transferring data from the European Economic Area, we may experience hesitancy, reluctance, or refusal by European or multinational customers to continue to use our services due to the potential risk exposure to such customers as a result of the ECJ ruling, and we and our customers are at risk of enforcement actions

taken by an EU data protection authority until such point in time that we ensure that all data transfers to us from the European Economic Area are legitimized. In addition, as the United Kingdom transitions out of the EU, we may encounter additional complexity with respect to data privacy.

With respect to all of the foregoing, any failure or perceived failure by us, our products or our platform to comply with U.S., EU or other foreign privacy or data security laws, policies, industry standards or legal obligations, or any security incident that results in the unauthorized access to, or acquisition, release or transfer of, personally identifiable information or other customer data may result in governmental investigations, inquiries, enforcement actions and prosecutions, private litigation, fines and penalties or adverse publicity. For example, on February 18, 2016, a putative class action complaint was filed in the Alameda County Superior Court in California. The complaint alleges that our products permit the interception, recording and disclosure of communications at a customer's request and in violation of the California Invasion of Privacy Act. The complaint seeks injunctive relief as well as monetary damages. We intend to vigorously defend this lawsuit and believe we have meritorious defenses; however, this litigation, any other such actions in the future and related penalties could divert management's attention and resources, adversely affect our brand, business, results of operations and financial condition.

We expect that there will continue to be new proposed laws, regulations and industry standards concerning privacy, data protection and information security in the United States, the European Union and other jurisdictions, and we cannot yet determine the impact such future laws, regulations and standards may have on our business. Because global laws, regulations and industry standards concerning privacy and data security have continued to develop and evolve rapidly, it is possible that we or our products or platform may not be, or may not have been, compliant with each such applicable law, regulation and industry standard.

Any such new laws, regulations, other legal obligations or industry standards, or any changed interpretation of existing laws, regulations or other standards may require us to incur additional costs and restrict our business operations. If our privacy or data security measures fail to comply with current or future laws, regulations, policies, legal obligations or industry standards, we may be subject to litigation, regulatory investigations, fines or other liabilities, as well as negative publicity and a potential loss of business.

Changes in laws and regulations related to the Internet or changes in the Internet infrastructure itself may diminish the demand for our products, and could adversely affect our business, results of operations and financial condition.

The future success of our business depends upon the continued use of the Internet as a primary medium for commerce, communications and business applications. Federal, state or foreign government bodies or agencies have in the past adopted, and may in the future adopt, laws or regulations affecting the use of the Internet as a commercial medium. Changes in these laws or regulations could require us to modify our products and platform in order to comply with these changes. In addition, government agencies or private organizations have imposed and may impose additional taxes, fees or other charges for accessing the Internet or commerce conducted via the Internet. These laws or charges could limit the growth of Internet-related commerce or communications generally, or result in reductions in the demand for Internet-based products and services such as our products and platform. In addition, the use of the Internet as a business tool could be adversely affected due to delays in the development or adoption of new standards and protocols to handle increased demands of Internet activity, security, reliability, cost, ease-of-use, accessibility and quality of service. The performance of the Internet and its acceptance as a business tool has been adversely affected by "viruses", "worms", and similar malicious programs. If the use of the Internet is reduced as a result of these or other issues, then demand for our products could decline, which could adversely affect our business, results of operations and financial condition.

Certain of our products are subject to telecommunications-related regulations, and future legislative or regulatory actions could adversely affect our business, results of operations and financial condition.

As a provider of communications products, we are subject to existing or potential FCC regulations relating to privacy, Telecommunications Relay Service Fund contributions and other requirements. FCC classification of our Internet voice communications products as telecommunications services could result in additional federal and state regulatory obligations. If we do not comply with FCC rules and regulations, we could be subject to FCC enforcement actions, fines, loss of licenses and possibly restrictions on our ability to operate or offer certain of our products. Any enforcement action by the FCC, which may be a public process, would hurt our reputation in the industry, possibly impair our ability to sell our products to customers and could adversely affect our business, results of operations and financial condition.

Our products are subject to a number of FCC regulations and laws that are administered by the FCC. Among others, we must comply (in whole or in part) with:

If we do not comply with any current or future rules or regulations that apply to our business, we could be subject to substantial fines and penalties, and we may have to restructure our offerings, exit certain markets or raise the price of our products. In addition, any uncertainty regarding whether particular regulations apply to our business, and how they apply, could increase our costs or limit our ability to grow. Any of the foregoing could adversely affect our business, results of operations and financial condition.

As we continue to expand internationally, we have become subject to telecommunications laws and regulations in the foreign countries where we offer our products. Internationally, we currently offer our products in over 180 countries.

Our international operations are subject to country-specific governmental regulation and related actions that have increased and may continue to increase our costs or impact our products and platform or prevent us from offering or providing our products in certain countries. Certain of our products may be used by customers located in countries where voice and other forms of IP communications may be illegal or require special licensing or in countries on a U.S. embargo list. Even where our products are reportedly illegal or become illegal or where users are located in an embargoed country, users in those countries may be able to continue to use our products in those countries notwithstanding the illegality or embargo. We may be subject to penalties or governmental action if consumers continue to use our products in countries where it is illegal to do so, and any such penalties or governmental action may be costly and may harm our business and damage our brand and reputation. We may be required to incur additional expenses to meet applicable international regulatory

requirements or be required to discontinue those services if required by law or if we cannot or will not meet those requirements.

If we are unable to effectively process local number and toll-free number portability provisioning in a timely manner or to obtain or retain direct inward dialing numbers and local or toll-free numbers, our business and results of operations may be adversely affected.

We support local number and toll-free number portability, which allows our customers to transfer their existing phone numbers to us and thereby retain their existing phone numbers when subscribing to our voice products. Transferring existing numbers is a manual process that can take up to 15 business days or longer to complete. A new customer of our voice products must maintain both our voice product and the customer's existing phone service during the number transferring process. Any delay that we experience in transferring these numbers typically results from the fact that we depend on network service providers to transfer these numbers, a process that we do not control, and these network service provider may refuse or substantially delay the transfer of these numbers to us. Local number portability is considered an important feature by many potential customers, and if we fail to reduce any related delays, then we may experience increased difficulty in acquiring new customers.

In addition, our future success depends in part on our ability to procure large quantities of local and toll-free direct inward dialing numbers, or DIDs, in the United States and foreign countries at a reasonable cost and without restrictions. Our ability to procure, distribute and retain DIDs depends on factors outside of our control, such as applicable regulations, the practices of network service providers that provide DIDs, such as offering DIDs with conditional minimum volume call level requirements, the cost of these DIDs and the level of overall competitive demand for new DIDs. Due to their limited availability, there are certain popular area code prefixes that we generally cannot obtain. Our inability to acquire or retain DIDs for our operations would make our voice and messaging products less attractive to potential customers in the affected local geographic areas. In addition, future growth in our customer base, together with growth in the customer bases of other providers of cloud communications, has increased, which increases our dependence on needing sufficiently large quantities of DIDs. It may become increasingly difficult to source larger quantities of DIDs as we scale and we may need to pay higher costs for DIDs, and DIDs may become subject to more stringent usage conditions. Any of the foregoing could adversely affect our business, results of operations and financial condition.

We face a risk of litigation resulting from customer misuse of our software to send unauthorized text messages in violation of the Telephone Consumer Protection Act.

Text messages may subject us to potential risks, including liabilities or claims relating to consumer protection laws. For example, the Telephone Consumer Protection Act of 1991 restricts telemarketing and the use of automatic SMS text messages without proper consent. This has resulted in civil claims against the Company and requests for information through third-party subpoenas. The scope and interpretation of the laws that are or may be applicable to the delivery of text messages are continuously evolving and developing. If we do not comply with these laws or regulations or if we become liable under these laws or regulations due to the failure of our customers to comply with these laws by obtaining proper consent, we could face direct liability.

We may be subject to governmental export controls and economic sanctions regulations that could impair our ability to compete in international markets due to licensing requirements and subject us to liability if we are not in compliance with applicable laws.

Various of our products and services may be subject to export control and economic sanctions regulations, including the U.S. Export Administration Regulations, U.S. Customs regulations and various economic and trade sanctions regulations administered by the U.S. Treasury Department's

Office of Foreign Assets Controls. Exports of our products and the provision of our services must be made in compliance with these laws and regulations. Although we take precautions to prevent our products from being provided in violation of such laws, we are aware of previous exports of certain of our products to a small number of persons and organizations that are the subject of U.S. sanctions or located in countries or regions subject to U.S. sanctions. If we fail to comply with these laws and regulations, we and certain of our employees could be subject to substantial civil or criminal penalties, including: the possible loss of export privileges; fines, which may be imposed on us and responsible employees or managers; and, in extreme cases, the incarceration of responsible employees or managers. Obtaining the necessary authorizations, including any required license, for a particular deployment may be time-consuming, is not guaranteed and may result in the delay or loss of sales opportunities. In addition, changes in our products or services, or changes in applicable export or economic sanctions regulations may create delays in the introduction and deployment of our products and services in international markets, or, in some cases, prevent the export of our products or provision of our services to certain countries or end users. Any change in export or economic sanctions regulations, shift in the enforcement or scope of existing regulations, or change in the countries, governments, persons or technologies targeted by such regulations, could also result in decreased use of our products and services, or in our decreased ability to export our products or provide our services to existing or prospective customers with international operations. Any decreased use of our products and services or limitation on our ability to export our products and provide our services could adversely affect our business, results of operations and financial condition.

Further, we incorporate encryption technology into certain of our products. Various countries regulate the import of certain encryption technology, including through import permitting and licensing requirements, and have enacted laws that could limit our customers' ability to import our products into those countries. Encryption products and the underlying technology may also be subject to export control restrictions. Governmental regulation of encryption technology and regulation of exports of encryption products, or our failure to obtain required approval for our products, when applicable, could harm our international sales and adversely affect our revenue. Compliance with applicable regulatory requirements regarding the export of our products and provision of our services, including with respect to new releases of our products and services, may create delays in the introduction of our products and services in international markets, prevent our customers with international operations from deploying our products and using our services throughout their globally-distributed systems or, in some cases, prevent the export of our products or provision of our services to some countries altogether.

We may have additional tax liabilities, which could harm our business, results of operations and financial condition.

Significant judgments and estimates are required in determining our provision for income taxes and other tax liabilities. Our tax expense may be impacted, for example, if tax laws change or are clarified to our detriment or if tax authorities successfully challenge the tax positions that we take, such as, for example, positions relating to the arms-length pricing standards for our intercompany transactions and our state sales and use tax positions. In determining the adequacy of income taxes, we assess the likelihood of adverse outcomes that could result if our tax positions were challenged by the Internal Revenue Service, or IRS, and other tax authorities. Should the IRS or other tax authorities assess additional taxes as a result of examinations, we may be required to record charges to operations that could adversely affect our results of operations and financial condition.

We could be subject to liability for historic and future sales, use and similar taxes, which could adversely affect our results of operations.

We conduct operations in many tax jurisdictions throughout the United States. In many of these jurisdictions, non-income-based taxes, such as sales and use and telecommunications taxes, are assessed

on our operations. We are subject to indirect taxes, and may be subject to certain other taxes, in some of these jurisdictions. Historically, we have not billed or collected these taxes and, in accordance with generally accepted accounting principles in the United States, or U.S. GAAP, we have recorded a provision for our tax exposure in these jurisdictions when it is both probable that a liability has been incurred and the amount of the exposure can be reasonably estimated. These estimates include several key assumptions including, but not limited to, the taxability of our products, the jurisdictions in which we believe we have nexus, and the sourcing of revenues to those jurisdictions. In the event these jurisdictions challenge our assumptions and analysis, our actual exposure could differ materially from our current estimates.

We are undergoing an audit in one jurisdiction and may be subject to additional scrutiny from state tax authorities in these or other jurisdictions and may have additional exposure related to our historic operations. Furthermore, certain jurisdictions in which we do not collect such taxes may assert that such taxes are applicable, which could result in tax assessments, penalties and interest, and we may be required to collect such taxes in the future. Such tax assessments, penalties and interest or future requirements may adversely affect our business, results of operations and financial condition.

Currently, we do not collect telecommunications-based taxes from our customers. We are developing the operational capability to collect these taxes from customers. When we begin to collect such taxes from customers, we may have some customers that question the incremental tax charges and some may seek to negotiate lower pricing from us, which could adversely affect our business, results of operations and financial condition.

Our global operations and structure subject us to potentially adverse tax consequences.

We generally conduct our global operations through subsidiaries and report our taxable income in various jurisdictions worldwide based upon our business operations in those jurisdictions. In particular, our intercompany relationships are subject to complex transfer pricing regulations administered by taxing authorities in various jurisdictions. Also, our tax expense could be affected depending on the applicability of withholding and other taxes (including withholding and indirect taxes on software licenses and related intercompany transactions) under the tax laws of certain jurisdictions in which we have business operations. The relevant revenue and taxing authorities may disagree with positions we have taken generally, or our determinations as to the value of assets sold or acquired or income and expenses attributable to specific jurisdictions. If such a disagreement were to occur, and our position were not sustained, we could be required to pay additional taxes, interest and penalties, which could result in one-time tax charges, higher effective tax rates, reduced cash flows and lower overall profitability of our operations.

Certain government agencies in jurisdictions where we and our affiliates do business have had an extended focus on issues related to the taxation of multinational companies. In addition, the Organization for Economic Co-operation and Development is conducting a project focused on base erosion and profit shifting in international structures, which seeks to establish certain international standards for taxing the worldwide income of multinational companies. As a result of these developments, the tax laws of certain countries in which we and our affiliates do business could change on a prospective or retroactive basis, and any such changes could increase our liabilities for taxes, interest and penalties, and therefore could harm our business, cash flows, results of operations and financial position.

Changes in the U.S. taxation of international business activities or the adoption of other tax reform policies could materially impact our business, results of operations and financial condition.

Changes to U.S. tax laws that may be enacted in the future could impact the tax treatment of our foreign earnings. Due to the expansion of our international business activities, any changes in the U.S. taxation of such activities may increase our worldwide effective tax rate and adversely affect our business, results of operations and financial condition.

If we experience excessive credit card or fraudulent activity, we could incur substantial costs.

Most of our customers authorize us to bill their credit card accounts directly for service fees that we charge. If people pay for our subscriptions with stolen credit cards, we could incur substantial third-party vendor costs for which we may not be reimbursed. Further, our customers provide us with credit card billing information online, and we do not review the physical credit cards used in these transactions, which increases our risk of exposure to fraudulent activity. We also incur charges, which we refer to as chargebacks, from the credit card companies from claims that the customer did not authorize the credit card transaction to purchase our subscription. If the number of unauthorized credit card transactions becomes excessive, we could be assessed substantial fines for excess chargebacks and we could lose the right to accept credit cards for payment.

Our products may also be subject to fraudulent usage, including but not limited to revenue share fraud, domestic traffic pumping, subscription fraud, premium text message scams and other fraudulent schemes. Although our customers are required to set passwords or personal identification numbers to protect their accounts, third parties have in the past been, and may in the future be, able to access and use their accounts through fraudulent means. Furthermore, spammers attempt to use our products to send targeted and untargeted spam messages. We cannot be certain that our efforts to defeat spamming attacks will be able to eliminate all spam messages from being sent using our platform. In addition, a cybersecurity breach of our customers' systems could result in exposure of their authentication credentials, unauthorized access to their accounts or fraudulent calls on their accounts, any of which could adversely affect our business, results of operations and financial condition.

Unfavorable conditions in our industry or the global economy or reductions in spending on information technology and communications could adversely affect our business, results of operations and financial condition.

Our results of operations may vary based on the impact of changes in our industry or the global economy on our customers. Our results of operations depend in part on demand for information technology and cloud communications. In addition, our revenue is dependent on the usage of our products, which in turn is influenced by the scale of business that our customers are conducting. To the extent that weak economic conditions result in a reduced volume of business for, and communications by, our customers and prospective customers, demand for, and use of, our products may decline. Furthermore, weak economic conditions may make it more difficult to collect on outstanding accounts receivable. Additionally, historically, we have generated the substantial majority of our revenue from small and medium-sized businesses, and we expect this to continue for the foreseeable future. Small and medium-sized business may be affected by economic downturns to a greater extent than enterprises, and typically have more limited financial resources, including capital-borrowing capacity, than enterprises. If our customers reduce their use of our products, or prospective customers delay adoption or elect not to adopt our products, as a result of a weak economy, this could adversely affect our business, results of operations and financial condition.

We may require additional capital to support our business, and this capital might not be available on acceptable terms, if at all.

We intend to continue to make investments to support our business and may require additional funds. In particular, we may seek additional funds to develop new products and enhance our platform and existing products, expand our operations, including our sales and marketing organizations and our presence outside of the United States, improve our infrastructure or acquire complementary businesses, technologies, services, products and other assets. In addition, we may use a portion of our cash to satisfy tax withholding and remittance obligations related to outstanding restricted stock units. Accordingly, we may need to engage in equity or debt financings to secure additional funds. If we raise additional funds through future issuances of equity or convertible debt securities, our stockholders

could suffer significant dilution, and any new equity securities we issue could have rights, preferences and privileges superior to those of holders of our Class A and Class B common stock. Any debt financing that we may secure in the future could involve restrictive covenants relating to our capital raising activities and other financial and operational matters, which may make it more difficult for us to obtain additional capital and to pursue business opportunities. We may not be able to obtain additional financing on terms favorable to us, if at all. If we are unable to obtain adequate financing or financing on terms satisfactory to us when we require it, our ability to continue to support our business growth, scale our infrastructure, develop product enhancements and to respond to business challenges could be significantly impaired, and our business, results of operations and financial condition may be adversely affected.

Our credit facility contains restrictive and financial covenants that may limit our operating flexibility.

Our credit facility contains certain restrictive covenants that either limit our ability to, or require a mandatory prepayment in the event we, incur additional indebtedness and liens, merge with other companies or consummate certain changes of control, acquire other companies, engage in new lines of business, change business locations, make certain investments, pay dividends, make any payments on any subordinated debt, transfer or dispose of assets, amend certain material agreements, and enter into various specified transactions. We, therefore, may not be able to engage in any of the foregoing transactions unless we obtain the consent of our lender or prepay the outstanding amount under the credit facility. The credit facility also contains certain financial covenants and financial reporting requirements. Our obligations under the credit facility are secured by all of our property, with certain exceptions. We may not be able to generate sufficient cash flow or sales to meet the financial covenants or pay the principal and interest under the credit facility. Furthermore, our future working capital, borrowings, or equity financing could be unavailable to repay or refinance the amounts outstanding under the credit facility. In the event of a liquidation, our lender would be repaid all outstanding principal and interest prior to distribution of assets to unsecured creditors, and the holders of our Class A and Class B common stock would receive a portion of any liquidation proceeds only if all of our creditors, including our lender, were first repaid in full.

We face exposure to foreign currency exchange rate fluctuations, and such fluctuations could adversely affect our business, results of operations and financial condition.

As our international operations expand, our exposure to the effects of fluctuations in currency exchange rates grows. While we have primarily transacted with customers and business partners in U.S. dollars, we have transacted with customers in Japan in Japanese Yen, and expect to significantly expand the number of transactions with customers that are denominated in foreign currencies in the future as we expand our business internationally. We incur expenses for some of our network service provider costs outside of the United States in local currencies and for employee compensation and other operating expenses at our non-U.S. locations in the local currency for such locations. Fluctuations in the exchange rates between the U.S. dollar and other currencies could result in an increase to the U.S. dollar equivalent of such expenses.

In addition, our international subsidiaries maintain net assets that are denominated in currencies other than the functional operating currencies of these entities. As we continue to expand our international operations, we become more exposed to the effects of fluctuations in currency exchange rates. Accordingly, changes in the value of foreign currencies relative to the U.S. dollar can affect our results of operations due to transactional and translational remeasurements. As a result of such foreign currency exchange rate fluctuations, it could be more difficult to detect underlying trends in our business and results of operations. In addition, to the extent that fluctuations in currency exchange rates cause our results of operations to differ from our expectations or the expectations of our investors

and securities analysts who follow our stock, the trading price of our Class A common stock could be adversely affected.

We do not currently maintain a program to hedge transactional exposures in foreign currencies. However, in the future, we may use derivative instruments, such as foreign currency forward and option contracts, to hedge certain exposures to fluctuations in foreign currency exchange rates. The use of such hedging activities may not offset any or more than a portion of the adverse financial effects of unfavorable movements in foreign exchange rates over the limited time the hedges are in place. Moreover, the use of hedging instruments may introduce additional risks if we are unable to structure effective hedges with such instruments.

Our ability to use our net operating losses to offset future taxable income may be subject to certain limitations.

As of December 31, 2016, we had federal and state net operating loss carryforwards, or NOLs, of $104.0 million and $88.7 million, respectively, due to prior period losses. In general, under Section 382 of the Internal Revenue Code of 1986, as amended, or the Code, a corporation that undergoes an "ownership change" (generally defined as a greater than 50-percentage-point cumulative change (by value) in the equity ownership of certain stockholders over a rolling three-year period) is subject to limitations on its ability to utilize its pre-change NOLs to offset post-change taxable income. Our existing NOLs may be subject to limitations arising from previous ownership changes, and if we undergo an ownership change in the future, our ability to utilize NOLs could be further limited by Section 382 of the Code. Future changes in our stock ownership, some of which may be outside of our control, could result in an ownership change under Section 382 of the Code. There is also a risk that due to regulatory changes, such as suspensions on the use of NOLs, or other unforeseen reasons, our existing NOLs could expire or otherwise be unavailable to offset future income tax liabilities. For these reasons, we may not be able to realize a tax benefit from the use of our NOLs, even if we attain profitability.

If our estimates or judgments relating to our critical accounting policies prove to be incorrect, our results of operations could be adversely affected.

The preparation of financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the amounts reported in the consolidated financial statements and accompanying notes. We base our estimates on historical experience and on various other assumptions that we believe to be reasonable under the circumstances, as provided in "Management's Discussion and Analysis of Financial Condition and Results of Operations." The results of these estimates form the basis for making judgments about the carrying values of assets, liabilities and equity, and the amount of revenue and expenses that are not readily apparent from other sources. Significant assumptions and estimates used in preparing our consolidated financial statements include those related to revenue recognition, capitalized internal-use software costs, other non-income taxes, business combination and valuation of goodwill and purchased intangible assets and stock-based compensation. Our results of operations may be adversely affected if our assumptions change or if actual circumstances differ from those in our assumptions, which could cause our results of operations to fall below the expectations of securities analysts and investors, resulting in a decline in the trading price of our Class A common stock.

Changes in financial accounting standards or practices may cause adverse, unexpected financial reporting fluctuations and affect our results of operations.

A change in accounting standards or practices may have a significant effect on our results of operations and may even affect our reporting of transactions completed before the change is effective. New accounting pronouncements and varying interpretations of accounting pronouncements have

occurred and may occur in the future. Changes to existing rules or the questioning of current practices may adversely affect our reported financial results or the way we conduct our business.

If we fail to maintain an effective system of disclosure controls and internal control over financial reporting, our ability to produce timely and accurate financial statements or comply with applicable regulations could be impaired.

As a public company, we are subject to the reporting requirements of the Exchange Act, the Sarbanes-Oxley Act of 2002, or the Sarbanes-Oxley Act, and the rules and regulations of the applicable listing standards of the New York Stock Exchange. We expect that the requirements of these rules and regulations will continue to increase our legal, accounting, and financial compliance costs, make some activities more difficult, time-consuming and costly and place significant strain on our personnel, systems and resources.

The Sarbanes-Oxley Act requires, among other things, that we maintain effective disclosure controls and procedures and internal control over financial reporting. Our disclosure controls and other procedures are designed to ensure that information required to be disclosed by us in the reports that we will file with the SEC is recorded, processed, summarized and reported within the time periods specified in SEC rules and forms and that information required to be disclosed in reports under the Exchange Act is accumulated and communicated to our principal executive and financial officers, and we continue to evaluate how to improve controls. We are also continuing to improve our internal control over financial reporting. In order to maintain and improve the effectiveness of our disclosure controls and procedures and internal control over financial reporting, we have expended, and anticipate that we will continue to expend, significant resources, including accounting-related costs and significant management oversight.

Our current controls and any new controls that we develop may become inadequate because of changes in conditions in our business. Further, weaknesses in our disclosure controls and internal control over financial reporting may be discovered in the future. Any failure to develop or maintain effective controls or any difficulties encountered in their implementation or improvement could harm our results of operations or cause us to fail to meet our reporting obligations and may result in a restatement of our financial statements for prior periods. Any failure to implement and maintain effective internal control over financial reporting also could adversely affect the results of periodic management evaluations and annual independent registered public accounting firm attestation reports regarding the effectiveness of our internal control over financial reporting that we will eventually be required to include in our periodic reports that will be filed with the SEC. Ineffective disclosure controls and procedures and internal control over financial reporting could also cause investors to lose confidence in our reported financial and other information, which would likely have a negative effect on the trading price of our Class A common stock. In addition, if we are unable to continue to meet these requirements, we may not be able to remain listed on the New York Stock Exchange. We are not currently required to comply with the SEC rules that implement Section 404 of the Sarbanes-Oxley Act and are therefore not required to make a formal assessment of the effectiveness of our internal control over financial reporting for that purpose. As a public company, we are required to provide an annual management report on the effectiveness of our internal control over financial reporting commencing with our second Annual Report on Form 10-K.

Our independent registered public accounting firm is not required to formally attest to the effectiveness of our internal control over financial reporting until after we are no longer an "emerging growth company" as defined in the JOBS Act. At such time, our independent registered public accounting firm may issue a report that is adverse in the event it is not satisfied with the level at which our internal control over financial reporting is documented, designed or operating. Any failure to maintain effective disclosure controls and internal control over financial reporting could have a material

and adverse effect on our business, results of operations and financial condition and could cause a decline in the trading price of our Class A common stock.

If our goodwill or intangible assets become impaired, we may be required to record a significant charge to earnings.

We review our intangible assets for impairment when events or changes in circumstances indicate the carrying value may not be recoverable. Goodwill is required to be tested for impairment at least annually. As of December 31, 2016, we carried a net $12.1 million of goodwill and intangible assets related to acquired businesses. An adverse change in market conditions, particularly if such change has the effect of changing one of our critical assumptions or estimates, could result in a change to the estimation of fair value that could result in an impairment charge to our goodwill or intangible assets. Any such charges may adversely affect our results of operations.

We are an "emerging growth company" and we cannot be certain if the reduced disclosure requirements applicable to emerging growth companies will make our Class A common stock less attractive to investors.

We are an "emerging growth company," as defined in the JOBS Act, and take advantage of certain exemptions from various reporting requirements that are applicable to other public companies that are not "emerging growth companies," including not being required to comply with the auditor attestation requirements of Section 404 of the Sarbanes-Oxley Act, reduced disclosure obligations regarding executive compensation in our periodic reports and proxy statements, and exemptions from the requirements of holding a nonbinding advisory vote on executive compensation and stockholder approval of any golden parachute payments not previously approved. We may take advantage of these exemptions for so long as we are an "emerging growth company." We cannot predict if investors will find our Class A common stock less attractive because we will rely on these exemptions. If some investors find our Class A common stock less attractive as a result, there may be a less active trading market for our Class A common stock and the trading price of our Class A common stock may be more volatile.

Our business is subject to the risks of earthquakes, fire, floods and other natural catastrophic events, and to interruption by man-made problems such as power disruptions, computer viruses, data security breaches or terrorism.

Our corporate headquarters are located in the San Francisco Bay Area, a region known for seismic activity. A significant natural disaster, such as an earthquake, fire or a flood, occurring at our headquarters, at one of our other facilities or where a business partner is located could adversely affect our business, results of operations and financial condition. Further, if a natural disaster or man-made problem were to affect our network service providers or Internet service providers, this could adversely affect the ability of our customers to use our products and platform. In addition, natural disasters and acts of terrorism could cause disruptions in our or our customers' businesses, national economies or the world economy as a whole. We also rely on our network and third-party infrastructure and enterprise applications and internal technology systems for our engineering, sales and marketing and operations activities. Although we maintain incident management and disaster response plans, in the event of a major disruption caused by a natural disaster or man-made problem, we may be unable to continue our operations and may endure system interruptions, reputational harm, delays in our development activities, lengthy interruptions in service, breaches of data security and loss of critical data, any of which could adversely affect our business, results of operations and financial condition.

In addition, computer malware, viruses and computer hacking, fraudulent use attempts and phishing attacks have become more prevalent in our industry, have occurred on our platform in the past and may occur on our platform in the future. Though it is difficult to determine what, if any, harm may directly result from any specific interruption or attack, any failure to maintain performance,

reliability, security and availability of our products and technical infrastructure to the satisfaction of our users may harm our reputation and our ability to retain existing users and attract new users.

The trading price of our Class A common stock has been volatile and may continue to be volatile, and you could lose all or part of your investment.

Prior to our initial public offering, there was no public market for shares of our Class A common stock. On June 23, 2016, we sold shares of our Class A common stock to the public at $15.00 per share. From June 23, 2016, the date that our Class A common stock started trading on the New York Stock Exchange, through January 31, 2017, the trading price of our Class A common stock has ranged from $23.66 per share to $70.96 per share. The trading price of our Class A common stock may continue to fluctuate significantly in response to numerous factors, many of which are beyond our control, including:

In addition, in the past, following periods of volatility in the overall market and the market price of a particular company's securities, securities class action litigation has often been instituted against these companies. This litigation, if instituted against us, could result in substantial costs and a diversion of our management's attention and resources.

Substantial future sales of shares of our Class A common stock could cause the market price of our Class A common stock to decline.

The market price of our Class A common stock could decline as a result of substantial sales of our Class A common stock, particularly sales by our directors, executive officers and significant stockholders, or the perception in the market that holders of a large number of shares intend to sell their shares.

Additionally, the shares of Class A common stock subject to outstanding options and restricted stock unit awards under our equity incentive plans and the shares reserved for future issuance under our equity incentive plans will become eligible for sale in the public market upon issuance. Certain holders of our Class A common stock have rights, subject to some conditions, to require us to file registration statements covering their shares or to include their shares in registration statements that we may file for our stockholders or ourselves.

The dual class structure of our common stock has the effect of concentrating voting control with those stockholders who held our capital stock prior to the completion of our initial public offering, including our directors, executive officers and significant stockholders and their respective affiliates who held in the aggregate 83.9% of the voting power of our capital stock as of December 31, 2016. This limits or precludes your ability to influence corporate matters, including the election of directors, amendments of our organizational documents and any merger, consolidation, sale of all or substantially all of our assets, or other major corporate transaction requiring stockholder approval.

Our Class B common stock has 10 votes per share, and our Class A common stock has one vote per share. As of December 31, 2016, our directors, executive officers and holders of more than 5% of our common stock, and their respective affiliates, hold in the aggregate 83.9% of the voting power of our capital stock. Because of the 10-to-one voting ratio between our Class B common stock and Class A common stock, the holders of our Class B common stock collectively will continue to control a majority of the combined voting power of our common stock and therefore be able to control all matters submitted to our stockholders for approval until the earlier of (i) June 22, 2023, or (ii) the date the holders of two-thirds of our Class B common stock elect to convert the Class B common stock to Class A common stock. This concentrated control limits or preclude your ability to influence corporate matters for the foreseeable future, including the election of directors, amendments of our organizational documents, and any merger, consolidation, sale of all or substantially all of our assets, or other major corporate transaction requiring stockholder approval. In addition, this may prevent or discourage unsolicited acquisition proposals or offers for our capital stock that you may feel are in your best interest as one of our stockholders.

Future transfers by holders of Class B common stock will generally result in those shares converting to Class A common stock, subject to limited exceptions, such as certain transfers effected for estate planning purposes. The conversion of Class B common stock to Class A common stock will have the effect, over time, of increasing the relative voting power of those holders of Class B common stock who retain their shares in the long term.

If securities or industry analysts cease publishing research or reports about us, our business or our market, or if they change their recommendations regarding our Class A common stock adversely, the trading price of our Class A common stock and trading volume could decline.

The trading market for our Class A common stock is influenced by the research and reports that securities or industry analysts may publish about us, our business, our market or our competitors. If any of the analysts who cover us change their recommendation regarding our Class A common stock adversely, or provide more favorable relative recommendations about our competitors, the trading price of our Class A common stock would likely decline. If any analyst who covers us were to cease coverage of our company or fail to regularly publish reports on us, we could lose visibility in the financial markets, which in turn could cause the trading price of our Class A common stock or trading volume to decline.

Anti-takeover provisions contained in our amended and restated certificate of incorporation and amended and restated bylaws, as well as provisions of Delaware law, could impair a takeover attempt.

Our amended and restated certificate of incorporation, amended and restated bylaws and Delaware law contain provisions which could have the effect of rendering more difficult, delaying, or preventing an acquisition deemed undesirable by our board of directors. Among other things, our amended and restated certificate of incorporation and amended and restated bylaws include provisions:

These provisions, alone or together, could delay or prevent hostile takeovers and changes in control or changes in our management.

As a Delaware corporation, we are also subject to provisions of Delaware law, including Section 203 of the Delaware General Corporation law, which prevents certain stockholders holding more than 15% of our outstanding common stock from engaging in certain business combinations without approval of the holders of at least two-thirds of our outstanding common stock not held by such 15% or greater stockholder.

Any provision of our amended and restated certificate of incorporation, amended and restated bylaws or Delaware law that has the effect of delaying, preventing or deterring a change in control could limit the opportunity for our stockholders to receive a premium for their shares of our common stock and could also affect the price that some investors are willing to pay for our Class A common stock.

We do not anticipate declaring any cash dividends to holders of our common stock in the foreseeable future. Consequently, investors may need to rely on sales of their Class A common stock after price appreciation, which may never occur, as the only way to realize any future gains on their investment. Investors seeking cash dividends should not purchase our Class A common stock. In addition, our credit facility contains restrictions on our ability to pay dividends.

In January 2016, we entered into a lease agreement, as subsequently amended, for approximately 90,000 square feet of new office space at 375 Beale Street in San Francisco that housed our principal executive office as of December 31, 2016. This office space replaced our existing principal executive office at 645 Harrison Street in San Francisco, for which the lease expired in January 2017.

The term of the 375 Beale Street lease is approximately 96 months following the commencement in October 2016, and the lease payments range from $0.4 million per month in the first 60 months to $0.5 million per month thereafter. We secured our lease obligation with a $7.4 million letter of credit, which we designated as restricted cash on our balance sheet as of December 31, 2016. We have a maximum $8.3 million of tenant improvement allowance available under this lease, of which $2.6 million was collected as of December 31, 2016.

In addition to our headquarters, we lease space in Mountain View, California, Tallinn, Estonia, Bogota, Colombia, Madrid, Spain, and Malmo, Sweden as additional research and development offices. We also lease space for additional sales and marketing offices in the following cities: New York, Dublin, London, Munich, Hong Kong and Singapore. Our Dublin office is our international headquarters.

We lease all of our facilities and do not own any real property. We intend to procure additional space in the future as we continue to add employees and expand geographically. We believe our facilities are adequate and suitable for our current needs and that, should it be needed, suitable additional or alternative space will be available to accommodate our operations.

On April 30, 2015, Telesign Corporation, or Telesign, filed a lawsuit against us in the United States District Court, Central District of California ("Telesign I"). Telesign alleges that we are infringing three U.S. patents that it holds: U.S. Patent No. 8,462,920 ("'920"), U.S. Patent No. 8,687,038 ("'038") and U.S. Patent No. 7,945,034 ("'034"). The patent infringement allegations in the lawsuit relate to our Programmable Authentication products, our two-factor authentication use case and an API tool to find information about a phone number. We have petitioned the U.S. Patent and Trademark Office for inter partes review of the patents at issue. On March 9, 2016, the District Court stayed the court case pending the resolution of those proceedings. On June 28, 2016, the Patent and Trademark Office instituted the inter partes review of the '034 patent, briefing on which has now begun, including Telesign's contingent motion to amend the '034 patent. On July 8, 2016, the Patent and Trademark Office denied our petition for inter partes review of the '920 and '038 patents. We subsequently petitioned for rehearing on this decision, and the request for rehearing was fully briefed by both parties on October 11, 2016. On July 20, 2016, Telesign applied to the court to lift the stay on Telesign I. We opposed the request, and on September 15, 2016, the court denied the request to lift the stay on Telesign I. On November 15, 2016, the Patent and Trademark Office denied our request for rehearing on the denied petitions for inter partes review. On December 20, 2016, we filed a reply to Telesign's

opposition to the '034 inter partes review and simultaneously filed an opposition to Telesign's motion to amend the '034 patent. On January 23, 2017, Telesign filed its reply to our opposition to the motion to amend. The hearing on the '034 inter partes review is scheduled for March 2017.

On March 28, 2016, Telesign filed a second lawsuit against us in the United States District Court, Central District of California ("Telesign II"), alleging infringement of U.S. Patent No. 9,300,792 ("'792") held by Telesign. The '792 patent is in the same patent family as the '920 and '038 patents asserted in Telesign I, and the infringement allegations in Telesign II relate to our Programmable Authentication products and our two-factor authentication use case. On May 23, 2016, we moved to dismiss the complaint in Telesign II. On August 3, 2016, the United States District Court, Central District of California, issued an order granting Twilio's motion to dismiss Telesign's complaint with leave to amend. Telesign filed an amended complaint on September 2, 2016 and we moved to dismiss the amended complaint on September 16, 2016. On November 7, 2016, our motion to dismiss was denied, and we filed our answer to the first amended complaint on November 21, 2016. With respect to each of the patents asserted in Telesign I and Telesign II, the complaints seek, among other things, to enjoin us from allegedly infringing the patents along with damages for lost profits.

On December 1, 2016, we filed a patent infringement lawsuit against Telesign in the United States District Court, Northern District of California, alleging indirect infringement of Unites States Patent No. 8,306,021, United States Patent No. 8,837,465, United States Patent No. 8,755,376, United States Patent No. 8,736,051, United States Patent No. 8,737,962, United States Patent No. 9,270,833, and United States Patent No. 9,226,217. Telesign filed a motion to dismiss the complaint on January 25, 2017.

On February 18, 2016, a putative class action complaint was filed in the Alameda County Superior Court in California, entitled Angela Flowers v. Twilio Inc. The complaint alleges that our products permit the interception, recording and disclosure of communications at a customer's request and are in violation of the California Invasion of Privacy Act. The complaint seeks injunctive relief as well as monetary damages. On May 27, 2016, we filed a demurrer to the complaint. On August 2, 2016, the court issued an order denying the demurrer in part and granted it in part, with leave to amend by August 18, 2016 to address any claims under California's Unfair Competition Law. The plaintiff opted not to amend the complaint. Discovery has already begun, and will continue until August 2017, when the plaintiff must file their motion for class certification.

We intend to vigorously defend these lawsuits and believe we have meritorious defenses to each. However, litigation is inherently uncertain, and any judgment or injunctive relief entered against us or any adverse settlement could negatively affect our business, results of operations and financial condition.

In addition to the litigation discussed above, from time to time, we may be subject to legal actions and claims in the ordinary course of business. We have received, and may in the future continue to receive, claims from third parties asserting, among other things, infringement of their intellectual property rights. Future litigation may be necessary to defend ourselves, our partners and our customers by determining the scope, enforceability and validity of third-party proprietary rights, or to establish our proprietary rights. The results of any current or future litigation cannot be predicted with certainty, and regardless of the outcome, litigation can have an adverse impact on us because of defense and settlement costs, diversion of management resources, and other factors.

Item 5. Market for Registrant's Common Equity, Related Stockholder Matters and Issuer Purchases of Equity Securities

Our Class A common stock has been listed on the New York Stock Exchange under the symbol "TWLO" since June 23, 2016. Prior to that date, there was no public trading market for our Class A common stock. The following table sets forth for the periods indicated the high and low sale prices per share of our Class A common stock as reported on the New York Stock Exchange:

As of February 14, 2017, we had 190 holders of record of our Class A and Class B common stock. The actual number of stockholders is greater than this number of record holders and includes stockholders who are beneficial owners but whose shares are held in street name by brokers and other nominees.

We have never declared or paid any cash dividends on our capital stock. We intend to retain any future earnings and do not expect to pay any dividends in the foreseeable future. In addition, the terms of our credit facility contain restrictions on our ability to declare and pay cash dividends on our capital stock.

This performance graph shall not be deemed "soliciting material" or to be "filed" with the SEC for purposes of Section 18 of the Securities Exchange Act of 1934, as amended (Exchange Act), or otherwise subject to the liabilities under that Section, and shall not be deemed to be incorporated by reference into any filing of Twilio Inc. under the Securities Act or the Exchange Act

We have presented below the cumulative total return to our stockholders between June 23, 2016 (the date our Class A common stock commenced trading on the NYSE) through December 31, 2016 in comparison to the NYSE Composite Index and Standard & Poor Systems Software Index. All values assume a $100 initial investment and data for the NYSE Composite Index and Standard & Poor Systems Software Index assume reinvestment of dividends. The comparisons are based on historical

data and are not indicative of, nor intended to forecast, the future performance of our Class A common stock.

The information required by this item with respect to our equity compensation plans is incorporated by reference to our Proxy Statement for the 2017 Annual Meeting of Stockholders to be filed with the Securities and Exchange Commission within 120 days of the fiscal year ended December 31, 2016.

Recent Sales of Unregistered Securities and Use of Proceeds from Registered Securities

From January 1, 2016 through December 31, 2016, we issued and sold to our employees, consultants and other service providers an aggregate of unregistered shares as follows: (a) 2,294,652 shares of common stock upon the exercise of options under our 2008 Stock Option Plan, or our 2008 Plan, at exercise prices ranging from $0.09 to $11.50 per share, for an aggregate exercise price of $9.1 million; and (b) 41,309 shares of common stock upon vesting of restricted stock units under our 2008 Plan with a total market value of $1.5 million.

In June 2016, we closed our initial public offering ("IPO"), in which we sold 11,500,000 shares of Class A common stock at a price to the public of $15.00 per share, including shares sold in connection with the exercise of the underwriters' option to purchase additional shares. The offer and sale of all of

the shares in the IPO were registered under the Securities Act pursuant to a registration statement on Form S-1 (File No. 333-211634), which was declared effective by the SEC on June 22, 2016. We raised $155.5 million in net proceeds after deducting underwriting discounts and commissions of $12.1 million and offering expenses of $4.9 million. No payments were made by us to directors, officers or persons owning 10 percent or more of our capital stock or to their associates, or to our affiliates, other than payments in the ordinary course of business to officers for salaries. There has been no material change in the planned use of proceeds from our IPO as described in our final prospectus filed with the SEC on June 23, 2016 pursuant to Rule 424(b). We invested the funds received in accordance with our board-approved investment policy, which provides for investments in obligations of the U.S. government, money market instruments, registered money market funds and corporate bonds. The managing underwriters of our IPO were Goldman, Sachs & Co. and J.P. Morgan Securities LLC.

In October 2016, we closed our follow-on public offering, in which we sold 1,691,222 shares of Class A common stock at a price to the public of $40.00 per share, including shares sold in connection with the exercise of the underwriters' option to purchase additional shares. The offer and sale of all of the shares in the follow-on offering were registered under the Securities Act pursuant to a registration statement on Form S-1 (File No. 333-214034), which was declared effective by the SEC on October 20, 2016. We raised $64.4 million in net proceeds after deducting underwriting discounts and commissions and offering expenses paid and payable by us. No payments were made by us to directors, officers or persons owning 10 percent or more of our capital stock or to their associates, or to our affiliates, other than payments in the ordinary course of business to officers for salaries. There has been no material change in the planned use of proceeds from our follow-on offering as described in our final prospectus filed with the SEC on October 21, 2016 pursuant to Rule 424(b). We invested the funds received in accordance with our board-approved investment policy, which provides for investments in obligations of the U.S. government, money market instruments, registered money market funds and corporate bonds. The managing underwriters of our follow-on offering were Goldman, Sachs & Co. and J.P. Morgan Securities LLC.

We have derived the selected consolidated statements of operations data for the years ended December 31, 2016, 2015 and 2014 and the Balance Sheet data as of December 31, 2016 and 2015 from our audited consolidated financial statements included elsewhere in this Annual Report on Form 10-K. Our historical results are not necessarily indicative of the results that may be expected in the future. The following selected consolidated financial and other data should be read in conjunction with Item 7, "Management's Discussion and Analysis of Financial Condition and Results of Operations", and our consolidated financial statements and the related notes appearing in Item 8, "Financial Statements and Supplementary Data", of this Annual Report on Form 10-K to fully understand factors that may affect the comparability of the information presented below.

	Year Ended December 31,

	2016			2015			2014
	(In thousands, except share, per share and customer data)
Consolidated Statement of Operations Data:
Revenue	$	277,335		$	166,919		$	88,846
Cost of revenue⁽¹⁾⁽²⁾		120,520			74,454			41,423

Gross profit		156,815			92,465			47,423

Operating expenses:
Research and development⁽¹⁾⁽²⁾		77,926			42,559			21,824
Sales and marketing⁽¹⁾		65,267			49,308			33,322
General and administrative⁽¹⁾⁽²⁾		51,077			35,991			18,960
Charitable contribution		3,860			—			—

Total operating expenses		198,130			127,858			74,106

Loss from operations		(41,315	)		(35,393	)		(26,683	)
Other income (expenses), net		317			11			(62	)

Loss before provision for income taxes		(40,998	)		(35,382	)		(26,745	)
Provision for income taxes		(326	)		(122	)		(13	)

Net loss		(41,324	)		(35,504	)		(26,758	)
Deemed dividend to investors in relation to tender offer		—			(3,392	)		—

Net loss attributable to common stockholders	$	(41,324	)	$	(38,896	)	$	(26,758	)



Net loss per share attributable to common stockholders, basic and diluted	$	(0.78	)	$	(2.19	)	$	(1.58	)



Weighted-average shares used in computing net loss per share attributable to common stockholders, basic and diluted		53,116,675			17,746,526			16,900,124



Key Business Metrics:
Number of Active Customer Accounts⁽³⁾ (as of end date of period)		36,606			25,347			16,631
Base Revenue⁽⁴⁾		245,548		$	136,851		$	75,697
Base Revenue Growth Rate		79	%		81	%		81	%
Dollar-Based Net Expansion Rate⁽⁵⁾		161	%		155	%		153	%

	As of December 31,

	2016		2015
	(In thousands)
Consolidated Balance Sheet Data:
Cash and cash equivalents	$	305,665	$	108,835
Working capital		279,676		96,032
Property and equipment, net		37,552		14,058
Total assets		412,694		157,516
Total stockholders' equity		329,447		116,625

We use the following non-GAAP financial information, collectively, to evaluate our ongoing operations and for internal planning and forecasting purposes. We believe that non-GAAP financial information, when taken collectively, may be helpful to investors because it provides consistency and comparability with past financial performance, facilitates period-to-period comparisons of results of operations, and assists in comparisons with other companies, many of which use similar non-GAAP financial information to supplement their GAAP results. Non-GAAP financial information is presented for supplemental informational purposes only, and should not be considered a substitute for financial information presented in accordance with generally accepted accounting principles, and may be different from similarly-titled non-GAAP measures used by other companies. Whenever we use a non-GAAP financial measure, a reconciliation is provided to the most closely applicable financial measure stated in accordance with generally accepted accounting principles. Investors are encouraged to review the related GAAP financial measures and the reconciliation of these non-GAAP financial measures to their most directly comparable GAAP financial measures.

Non-GAAP Gross Profit and Non-GAAP Gross Margin. We define non-GAAP gross profit and non-GAAP gross margin as GAAP gross profit and GAAP gross margin, respectively, adjusted to exclude stock-based compensation and amortization of acquired intangibles.

	Year Ended December 31,

	2016			2015
	(In thousands)
Reconciliation:
Gross profit	$	156,815		$	92,465
Non-GAAP adjustments:
Stock-based compensation		291			65
Amortization of acquired intangible assets		619			239

Non-GAAP gross profit	$	157,725		$	92,769



Non-GAAP gross margin		57	%		56	%

Non-GAAP Operating Expenses. We define non-GAAP operating expenses (including categories of operating expenses) as GAAP operating expenses (and categories of operating expenses) adjusted to exclude, as applicable, stock-based compensation, amortization of acquired intangibles, expenses related to stock repurchases, acquisition-related expenses, release of tax liability upon obligation settlement, charitable contribution and payroll taxes related to stock-based compensation.

	Year Ended December 31,

	2016			2015
	(In thousands)
Reconciliation:
Operating expenses	$	198,130		$	127,858
Non-GAAP adjustments:
Stock-based compensation		(23,934	)		(8,812	)
Amortization of acquired intangible assets		(261	)		(225	)
Stock repurchase		—			(1,965	)
Acquisition-related expenses		(499	)		(1,165	)
Release of tax liability upon obligation settlement		805			—
Charitable contribution		(3,860	)		—
Payroll taxes related to stock-based compensation		(434	)		—

Non-GAAP operating expenses	$	169,947		$	115,691

Non-GAAP Operating Loss and Non-GAAP Operating Margin. We define non-GAAP operating loss and non-GAAP operating margin as GAAP operating loss and GAAP operating margin, respectively, adjusted to exclude stock-based compensation, amortization of acquired intangibles,

expenses related to stock repurchases, acquisition-related expenses, release of tax liability upon obligation settlement, charitable contribution and payroll taxes related to stock-based compensation.

	Year Ended December 31,

	2016			2015
	(In thousands)
Reconciliation:
Loss from operations	$	(41,315	)	$	(35,393	)
Non-GAAP adjustments:
Stock-based compensation		24,225			8,877
Amortization of acquired intangible assets		880			464
Stock repurchase		—			1,965
Acquisition-related expenses		499			1,165
Release of tax liability upon obligation settlement		(805	)		—
Charitable contribution		3,860			—
Payroll taxes related to stock-based compensation		434			—

Non-GAAP loss from operations	$	(12,222	)	$	(22,922	)



Non-GAAP operating margin		(4	)%		(14	)%

Item 7. MANAGEMENT'S DISCUSSION AND ANALYSIS OF FINANCIAL CONDITION AND RESULTS OF OPERATIONS

The following discussion and analysis of our financial condition and results of operations should be read in conjunction with our consolidated financial statements and related notes appearing elsewhere in this Annual Report on Form 10-K. In addition to historical financial information, the following discussion contains forward-looking statements that is based upon current plans, expectations and beliefs that involve risks and uncertainties. Our actual results may differ materially from those anticipated in these forward-looking statements as a result of various factors, including those set forth under "Risk Factors" in this Annual Report on Form 10-K. Our fiscal year ends on December 31.

We are the leader in the Cloud Communications Platform category. We enable developers to build, scale and operate real-time communications within software applications.

Our developer-first platform approach consists of three things: our Programmable Communications Cloud, Super Network and Business Model for Innovators. Our Programmable Communications Cloud software enables developers to embed voice, messaging, video and authentication capabilities into their applications via our simple-to-use Application Programming Interfaces, or APIs. We do not aim to provide complete business solutions, rather our Programmable Communications Cloud offers flexible building blocks that enable our customers to build what they need. The Super Network is our software layer that allows our customers' software to communicate with connected devices globally. It interconnects with communications networks around the world and continually analyzes data to optimize the quality and cost of communications that flow through our platform. Our Business Model for Innovators empowers developers by reducing friction and upfront costs, encouraging experimentation, and enabling developers to grow as customers as their ideas succeed.

As of December 31, 2016, our customers' applications that are embedded with our products could reach users via voice, messaging and video in nearly every country in the world, and our platform offered customers local telephone numbers in over 50 countries and text-to-speech functionality in 26 languages. We support our global business through 26 cloud data centers in eight regions around the world and have developed contractual relationships with network service providers globally.

Our business model is primarily focused on reaching and serving the needs of developers. We established and maintain our leadership position by engaging directly with, and cultivating, our developer community, which has led to the rapid adoption of our platform. We reach developers through community events and conferences, including our SIGNAL developer conference, to demonstrate how every developer can create differentiated applications incorporating communications using our products.

Once developers are introduced to our platform, we provide them with a low-friction trial experience. By accessing our easy-to-configure APIs, extensive self-service documentation and customer support team, developers build our products into their applications and then test such applications through free trials. Once they have decided to use our products beyond the initial free trial period, customers provide their credit card information and only pay for the actual usage of our products. Historically, we have acquired the substantial majority of our customers through this self-service model. As customers expand their usage of our platform, our relationships with them often evolve to include business leaders within their organizations. Once our customers reach a certain spending level with us, we support them with account managers or customer success advocates within our sales organization to ensure their satisfaction and expand their usage of our products.

When potential customers do not have the available developer resources to build their own applications, we refer them to our network of Solution Partners, who embed our products in their

solutions, such as software for contact centers and sales force and marketing automation that they sell to other businesses.

We recently began to supplement our self-service model with a sales effort aimed at engaging larger potential customers, strategic leads and existing customers through an enterprise sales approach. We have supplemented this sales effort with a new product launch, Twilio Enterprise Plan, which provides new capabilities for advanced security, access management and granular administration. Our sales organization targets technical and business leaders who are seeking to leverage software to drive competitive differentiation. As we educate these leaders on the benefits of developing applications that incorporate our products to differentiate their business, they often consult with their developers regarding implementation. We believe that developers are often advocates for our products as a result of our developer-focused approach. Our sales organization includes sales development, inside sales, field sales and sales engineering personnel.

We generate the substantial majority of our revenue from customers based on their usage of our software products that they have incorporated into their applications. In addition, customers typically purchase one or more telephone numbers from us, for which we charge a monthly flat fee per number. Some customers also choose to purchase various levels of premium customer support for a monthly fee. Customers that register in our self-service model typically pay up-front via credit card and draw down their balance as they purchase or use our products. Most of our customers draw down their balance in the same month they pay up front and, as a result, our deferred revenue at any particular time is not a meaningful indicator of future revenue. As our customers' usage grows, some of our customers enter into contracts and are invoiced monthly in arrears. Many of these customer contracts have terms of 12 months and typically include some level of minimum revenue commitment. Most customers with minimum revenue commitment contracts generate a significant amount of revenue in excess of their minimum revenue commitment in any period. Historically, the aggregate minimum commitment revenue from customers with which we have contracts has constituted a minority of our revenue in any period, and we expect this to continue in the future.

Our developer-focused products are delivered to customers and users through our Super Network, which uses software to optimize communications on our platform. We interconnect with communications networks globally to deliver our products, and therefore we have arrangements with network service providers in many regions throughout the world. Historically, a substantial majority of our cost of revenue has been network service provider fees. We continue to optimize our network service provider coverage and connectivity through continuous improvements in routing and sourcing in order to lower the usage expenses we incur for network service provider fees. As we benefit from our platform optimization efforts, we sometimes pass these savings on to customers in the form of lower usage prices on our products in an effort to drive increased usage and expand the reach and scale of our platform. In the near term, we intend to operate our business to expand the reach and scale of our platform and to grow our revenue, rather than to maximize our gross margins.

We have achieved significant growth in recent periods. For the years ended December 31, 2016, 2015 and 2014, our revenue was $277.3 million, $166.9 million and $88.8 million, respectively. In 2016, 2015 and 2014, our 10 largest Active Customer Accounts generated an aggregate of 30%, 32% and 28%, respectively. For the years ended December 31, 2016, 2015 and 2014, among our 10 largest Active Customer Accounts we had three, two and one Variable Customer Accounts, respectively, representing 11%, 17% and 13%, respectively. For the years ended December 31, 2016, 2015 and 2014, our Base Revenue was $245.5 million, $136.9 million and $75.7 million, respectively. We incurred a net loss of $41.3 million, $35.5 million and $26.8 million for the years ended December 31, 2016, 2015 and 2014, respectively. See the section titled "—Key Business Metrics—Base Revenue" for a discussion of Base Revenue.

In June 2016, we completed an initial public offering ("IPO") in which we sold 11,500,000 shares of our newly authorized Class A common stock, which included 1,500,000 shares sold pursuant to the exercise by the underwriters of an option to purchase additional shares, at the public offering price of $15.00 per share. We received net proceeds of $155.5 million, after deducting underwriting discounts and commissions and offering expenses paid by us, from the sale of our shares in the IPO. Immediately prior to the completion of the IPO, all shares of common stock then outstanding were reclassified as shares of Class B common stock and all shares of convertible preferred stock then outstanding were converted into 54,508,441 shares of common stock on a one-to-one basis, and then reclassified as shares of Class B common stock. See Note 12 to the consolidated financial statements included elsewhere in this Annual Report on Form 10-K for further discussion of Class A and B common stock.

In October 2016, we completed a follow-on public offering in which we sold 1,691,222 shares of our Class A common stock, which included 1,050,000 shares sold pursuant to the exercise by the underwriters of an option to purchase additional shares, at a public offering price of $40.00 per share. In addition, another 6,358,778 shares of our Class A common stock were sold by our selling stockholders, which included 906,364 shares sold pursuant to the exercise of employee stock options by certain selling stockholders. We received aggregate proceeds of $64.4 million, after deducting underwriting discounts and commissions and estimated offering expenses paid and payable by us. Of the net proceeds we received in such offering, $3.9 million was reserved to fund and support the operations of Twilio.org, through which we donate and discount our products to nonprofits, who use our products to engage their audience, expand their reach and focus on making a meaningful change in the world, and the number of shares of our Class A common stock that was reserved for that purpose was reduced by 100,000. We did not receive any of the net proceeds from the sales of shares by the selling stockholders.

Number of Active Customer Accounts. We believe that the number of our Active Customer Accounts is an important indicator of the growth of our business, the market acceptance of our platform and future revenue trends. We define an Active Customer Account at the end of any period as an individual account, as identified by a unique account identifier, for which we have recognized at least $5 of revenue in the last month of the period. We believe that the use of our platform by our customers at or above the $5 per month threshold is a stronger indicator of potential future engagement than trial usage of our platform or usage at levels below $5 per month. A single organization may constitute multiple unique Active Customer Accounts if it has multiple account identifiers, each of which is treated as a separate Active Customer Account.

In the years ended December 31, 2016, 2015 and 2014, revenue from Active Customer Accounts represented over 99% of total revenue in each period.

Base Revenue. We monitor Base Revenue as one of the more reliable indicators of future revenue trends. Base Revenue consists of all revenue other than revenue from large Active Customer Accounts that have never entered into 12-month minimum revenue commitment contracts with us, which we refer to as Variable Customer Accounts. While almost all of our customer accounts exhibit some level of variability in the usage of our products, based on the experience of our management, we believe that Variable Customer Accounts are more likely to have significant fluctuations in usage of our products from period to period, and therefore that revenue from Variable Customer Accounts may also fluctuate significantly from period to period. This behavior is best evidenced by the decision of such customers not to enter into contracts with us that contain minimum revenue commitments, even though they may spend significant amounts on the use of our products and they may be foregoing more favorable terms often available to customers that enter into committed contracts with us. This variability adversely affects our ability to rely upon revenue from Variable Customer Accounts when analyzing expected trends in future revenue.

For historical periods through March 31, 2016, we defined a Variable Customer Account as an Active Customer Account that (i) had never signed a minimum revenue commitment contract with us for a term of at least 12 months and (ii) had met or exceeded 1% of our revenue in any quarter in the periods presented through March 31, 2016. To allow for consistent period-to-period comparisons, in the event a customer account qualified as a Variable Customer Account as of March 31, 2016, or a previously Variable Customer Account ceased to be an Active Customer Account as of such date, we included such customer account as a Variable Customer Account in all periods presented. For reporting periods starting with the three months ended June 30, 2016, we define a Variable Customer Account as a customer account that (a) has been categorized as a Variable Customer Account in any prior quarter, as well as (b) any new customer account that (i) is with a customer that has never signed a minimum revenue commitment contract with us for a term of at least 12 months and (ii) meets or exceeds 1% of our revenue in a quarter. Once a customer account is deemed to be a Variable Customer Account in any period, it remains a Variable Customer Account in subsequent periods unless such customer enters into a minimum revenue commitment contract with us for a term of at least 12 months.

In the years ended December 31, 2016, 2015 and 2014, we had eight, nine and ten Variable Customer Accounts, which represented 11%, 18% and 15%, respectively, of our total revenue.

Dollar-Based Net Expansion Rate. Our ability to drive growth and generate incremental revenue depends, in part, on our ability to maintain and grow our relationships with existing Active Customer Accounts and to increase their use of the platform. An important way in which we track our performance in this area is by measuring the Dollar-Based Net Expansion Rate for our Active Customer Accounts, other than our Variable Customer Accounts. Our Dollar-Based Net Expansion Rate increases when such Active Customer Accounts increase usage of a product, extend usage of a product to new applications or adopt a new product. Our Dollar-Based Net Expansion Rate decreases when such Active Customer Accounts cease or reduce usage of a product or when we lower usage prices on a product. As our customers grow their businesses and extend the use of our platform, they sometimes create multiple customer accounts with us for operational or other reasons. As such, for reporting periods starting with the three months ended December 31, 2016, when we identify a significant customer organization (defined as a single customer organization generating more than 1% of revenue in a quarterly reporting period) that has created a new Active Customer Account, this new Active Customer Account is tied to, and revenue from this new Active Customer Account is included with, the original Active Customer Account for the purposes of calculating this metric. We believe measuring our Dollar-Based Net Expansion Rate on revenue generated from our Active Customer Accounts, other than our Variable Customer Accounts, provides a more meaningful indication of the performance of our efforts to increase revenue from existing customers.

Our Dollar-Based Net Expansion Rate compares the revenue from Active Customer Accounts, other than Variable Customer Accounts, in a quarter to the same quarter in the prior year. To calculate

the Dollar-Based Net Expansion Rate, we first identify the cohort of Active Customer Accounts, other than Variable Customer Accounts, that were Active Customer Accounts in the same quarter of the prior year. The Dollar-Based Net Expansion Rate is the quotient obtained by dividing the revenue generated from that cohort in a quarter, by the revenue generated from that same cohort in the corresponding quarter in the prior year. When we calculate Dollar-Based Net Expansion Rate for periods longer than one quarter, we use the average of the applicable quarterly Dollar-Based Net Expansion Rates for each of the quarters in such period.

In November 2016, we acquired certain assets of Tikal Technologies S.L., a Spanish corporation, behind its Kurento Open Source Project, consisting of proprietary WebRTC media processing technologies, certain licenses, patents and trademarks and employee relationships behind the WebRTC technology. The purchase price consisted of $8.5 million in cash, of which $1.5 million was placed into an escrow to protect us against breaches of general representations, warranties, claims and tax compliance matters. The escrow is effective for 24 months and 10 days from the acquisition date and may be extended under certain circumstances.

On August 21, 2015, we repurchased an aggregate of 365,916 shares of Series A preferred stock and Series B preferred stock from certain preferred stockholders, and repurchased an aggregate of 1,869,156 shares of common stock from certain current and former employees, for $22.8 million in cash, which transaction we refer to as the 2015 Repurchase. The 2015 Repurchase was conducted at a price in excess of the fair value of our common stock at the date of repurchase. No special rights or privileges were conveyed to the employees and former employees. However, not all employees were invited to participate in the 2015 Repurchase. We recorded a compensation expense in the amount of $2.0 million, which represented the excess of the common stock repurchase price above the fair value of the common stock on the date of repurchase. The excess of the preferred stock repurchase price above the carrying value of the preferred stock was recorded as a deemed dividend in the year ended December 31, 2015. We retired the shares repurchased in the 2015 Repurchase as of August 21, 2015.

At December 31, 2016, we had federal and state net operating loss carryforwards of approximately $104.0 million and $88.7 million, respectively, and federal and state tax credits of approximately $6.4 million and $5.4 million, respectively. If not utilized, the federal and state loss carryforwards will expire at various dates beginning in 2029 and 2027, respectively, and the federal tax credits will expire at various dates beginning in 2029. The state tax credits can be carried forward indefinitely. At present, we believe that it is more likely than not that the federal and state net operating loss and credit carryforwards will not be realized. Accordingly, a full valuation allowance has been established for these tax attributes, as well as the rest of the federal and state deferred tax assets.

Revenue. We derive our revenue primarily from usage-based fees earned from customers using the software products within our Programmable Communications Cloud. These usage-based software products include our Programmable Voice, Programmable Messaging and the recently introduced Programmable Video products. Some examples of the usage-based fees for which we charge include minutes of call duration activity for our Programmable Voice products, number of text messages sent or received using our Programmable Messaging products and number of authentications for our Programmable Authentication product. In 2016, 2015 and 2014, we generated 83%, 79% and 75% of our revenue, respectively, from usage-based fees. We also earn monthly flat fees from certain fee-based

products, such as telephone numbers and customer support. We do not generate any revenue directly from our Super Network or Business Model for Innovators.

Customers typically pay up-front via credit card in monthly prepaid amounts and draw down their balances as they purchase or use our products. As customers grow their usage of our products they automatically receive tiered usage discounts. Our larger customers often enter into contracts, for at least 12 months, that contain minimum revenue commitments, which may contain more favorable pricing. Customers on such contracts typically are invoiced monthly in arrears for products used.

Amounts that have been charged via credit card or invoiced are recorded in accounts receivable and in revenue or deferred revenue, depending on whether the revenue recognition criteria have been met. Given that our credit card prepayment amounts tend to be approximately equal to our credit card consumption amounts in each period, and that we do not have many invoiced customers on pre-payment contract terms, our deferred revenue at any particular time is not a meaningful indicator of future revenue.

We define U.S. revenue as revenue from customers with IP addresses at the time of registration in the United States, and we define international revenue as revenue from customers with IP addresses at the time of registration outside of the United States.

Cost of Revenue and Gross Margin. Cost of revenue consists primarily of fees paid to network service providers. Cost of revenue also includes cloud infrastructure fees, personnel costs, such as salaries and stock-based compensation for our customer support employees, and non-personnel costs, such as amortization of capitalized internal-use software development costs. Our arrangements with network service providers require us to pay fees based on the volume of phone calls initiated or text messages sent, as well as the number of telephone numbers acquired by us to service our customers. Our arrangements with our cloud infrastructure provider require us to pay fees based on our server capacity consumption.

Our gross margin has been and will continue to be affected by a number of factors, including the timing and extent of our investments in our operations, our ability to manage our network service provider and cloud infrastructure-related fees, the mix of U.S. revenue compared to international revenue, the timing of amortization of capitalized software development costs and the extent to which we periodically choose to pass on our cost savings from platform optimization efforts to our customers in the form of lower usage prices.

Operating Expenses. The most significant components of operating expenses are personnel costs, which consist of salaries, benefits, bonuses, stock-based compensation and compensation expenses related to stock repurchases from employees. We also incur other non-personnel costs related to our general overhead expenses. We expect that our operating costs will increase in absolute dollars.

Research and Development. Research and development expenses consist primarily of personnel costs, outsourced engineering services, cloud infrastructure fees for staging and development, amortization of capitalized internal-use software development costs and an allocation of our general overhead expenses. We capitalize the portion of our software development costs that meets the criteria for capitalization.

We continue to focus our research and development efforts on adding new features and products including new use cases, improving our platform and increasing the functionality of our existing products.

Sales and Marketing. Sales and marketing expenses consist primarily of personnel costs, including commissions for our sales employees. Sales and marketing expenses also include expenditures related to advertising, marketing, our brand awareness activities and developer evangelism, costs related to our SIGNAL developer conferences, credit card processing fees, professional services fees and an allocation of our general overhead expenses.

We focus our sales and marketing efforts on generating awareness of our company, platform and products through our developer evangelist team and self-service model, creating sales leads and establishing and promoting our brand, both domestically and internationally. We plan to continue investing in sales and marketing by increasing our sales and marketing headcount, supplementing our self-service model with an enterprise sales approach, expanding our sales channels, driving our go-to-market strategies, building our brand awareness and sponsoring additional marketing events.

General and Administrative. General and administrative expenses consist primarily of personnel costs for our accounting, finance, legal, human resources and administrative support personnel and executives. General and administrative expenses also include costs related to business acquisitions, legal and other professional services fees, sales and other taxes, depreciation and amortization and an allocation of our general overhead expenses. We expect that we will incur costs associated with supporting the growth of our business and to meet the increased compliance requirements associated with both our international expansion and our transition to, and operation as, a public company.

Our general and administrative expenses include a significant amount of sales and other taxes to which we are subject based on the manner we sell and deliver our products. Historically, we have not collected such taxes from our customers and have therefore recorded such taxes as general and administrative expenses. We expect that these expenses will decline in future years as we continue to implement our sales tax collection mechanisms and start collecting these taxes from our customers.

Provision for Income Taxes. Our provision for income taxes has not been historically significant to our business as we have incurred operating losses to date. Our provision for income taxes consists primarily of income taxes in certain foreign jurisdictions in which we conduct business.

The following tables set forth our results of operations for the periods presented in dollars and as a percentage of our total revenue for those periods. The period-to-period comparisons of our historical results are not necessarily indicative of the results that may be expected in the future.

	Year Ended December 31,

	2016			2015			2014
	(In thousands, except share and per share data)
Consolidated Statements of Operations Data:
Revenue	$	277,335		$	166,919		$	88,846
Cost of revenue⁽¹⁾⁽²⁾		120,520			74,454			41,423

Gross profit		156,815			92,465			47,423

Operating expenses:
Research and development⁽¹⁾⁽²⁾		77,926			42,559			21,824
Sales and marketing⁽¹⁾		65,267			49,308			33,322
General and administrative⁽¹⁾⁽²⁾		51,077			35,991			18,960
Charitable contribution		3,860			—			—

Total operating expenses		198,130			127,858			74,106

Loss from operations		(41,315	)		(35,393	)		(26,683	)
Other income (expenses), net		317			11			(62	)

Loss before provision for income taxes		(40,998	)		(35,382	)		(26,745	)
Provision for income taxes		(326	)		(122	)		(13	)

Net loss		(41,324	)		(35,504	)		(26,758	)
Deemed dividend to investors in relation to tender offer		—			(3,392	)		—

Net loss attributable to common stockholders	$	(41,324	)	$	(38,896	)	$	(26,758	)



Net loss per share attributable to common stockholders, basic and diluted	$	(0.78	)	$	(2.19	)	$	(1.58	)



Weighted-average shares used in computing net loss per share attributable to common stockholders, basic and diluted		53,116,675			17,746,526			16,900,124

	Year Ended December 31,

	2016			2015			2014
Consolidated Statements of Operations, as a percentage of revenue:**
Revenue		100	%		100	%		100	%
Cost of revenue		43			45			47

Gross profit		57			55			53

Operating expenses:
Research and development		28			25			25
Sales and marketing		24			30			38
General and administrative		18			22			21
Charitable contribution		1			—			—

Total operating expenses		71			77			83

Loss from operations		(15	)		(21	)		(30	)
Other income (expenses), net		*			*			*

Loss before provision for income taxes		(15	)		(21	)		(30	)
Provision for income taxes		*			*			*

Net loss		(15	)		(21	)		(30	)
Deemed dividend to investors in relation to tender offer		—			(2	)		—

Net loss attributable to common stockholders		(15	)%		(23	)%		(30	)%

In 2016, Base Revenue increased by $108.7 million, or 79%, compared to 2015, and represented 89% and 82% of total revenue in 2016 and 2015, respectively. This increase was primarily attributable to an increase in the usage of all our products, particularly our Programmable Messaging products and

Programmable Voice products, and the adoption of additional products by our existing customers. This increase was partially offset by pricing decreases that we have implemented over time for our customers in the form of lower usage prices in an effort to increase the reach and scale of our platform. The changes in usage and price in 2016 were reflected in our Dollar-Based Net Expansion Rate of 161%. The increase in usage was also attributable to a 44% increase in the number of Active Customer Accounts, from 25,347 as of December 31, 2015 to 36,606 as of December 31, 2016.

In 2016, Variable Revenue increased by $1.7 million, or 6%, compared to 2015, and represented 11% and 18% of total revenue in 2016 and 2015, respectively. This increase was primarily attributable to the increase in the usage of products by our existing Variable Customer Accounts, partially offset by the decrease in number of Variable Customer Accounts from nine to eight.

U.S. revenue and international revenue represented $233.9 million, or 84%, and $43.4 million, or 16%, respectively, of total revenue in 2016, compared to $143.1 million, or 86%, and $23.8 million, or 14%, respectively, of total revenue in 2015. The increase in international revenue in absolute dollars and as a percentage of total revenue was attributable to the growth in usage of our products, particularly our Programmable Messaging products and Programmable Voice products, by our existing international Active Customer Accounts and to a 61% increase in the number of international Active Customer Accounts, driven in part by our focus on expanding our sales to customers outside of the United States. We opened one office outside of the United States between December 31, 2015 and December 31, 2016.

In 2015, Base Revenue increased by $61.2 million, or 81%, compared to 2014, and represented 82% and 85% of total revenue in 2015 and 2014, respectively. This increase was primarily attributable to an increase in the usage of all our products, particularly our Programmable Messaging products and Programmable Voice products, and the adoption of additional products by our existing customers. This increase was partially offset by pricing decreases that we have implemented over time for our customers in the form of lower usage prices in an effort to increase the reach and scale of our platform. The changes in usage and price in 2015 were reflected in our Dollar-Based Net Expansion Rate of 155%. The increase in usage was also attributable to a 52% increase in the number of Active Customer Accounts, from 16,631 as of December 31, 2014 to 25,347 as of December 31, 2015.

In 2015, Variable Revenue increased by $16.9 million, or 129%, compared to 2014, and represented 18% and 15% of total revenue in 2015 and 2014, respectively. This increase was primarily attributable to the increase in the usage of products by our existing Variable Customer Accounts.

U.S. revenue and international revenue represented $143.1 million, or 86%, and $23.8 million, or 14%, respectively, of total revenue in 2015, compared to $78.3 million, or 88%, and $10.6 million, or 12%, respectively, of total revenue in 2014. The increase in international revenue in absolute dollars and as a percentage of total revenue was attributable to the growth in usage of our products, particularly our Programmable Messaging products and Programmable Voice products, by our existing international Active Customer Accounts and to a 78% increase in the number of international Active Customer Accounts, driven in part by our focus on expanding our sales to customers outside of the United States. We opened five offices outside of the United States between December 31, 2014 and December 31, 2015.

In 2016, cost of revenue increased by $46.1 million, or 62%, compared to 2015. The increase in cost of revenue was primarily attributable to a $40.0 million increase in network service providers' costs, a $2.8 million increase in cloud infrastructure fees to support the growth in usage of our products and a $1.9 million increase in amortization expense for internal-use software.

In 2016, gross margin improved primarily as a result of cost savings from our continued platform optimization efforts, along with changes in our product and geographic mix.

In 2015, cost of revenue increased by $33.0 million, or 80%, compared to 2014. The increase in cost of revenue was primarily attributable to a $28.6 million increase in network service providers' costs, a $2.6 million increase in cloud infrastructure fees to support the growth in usage of our products and a $1.2 million increase in amortization expense for internal-use software.

In 2015, gross margin improved primarily as a result of cost savings from our continued platform optimization efforts.

	Year Ended December 31,

	Year Ended December 31,						2015 to 2016 Change				2014 to 2015 Change
	2016		2015		2014		2015 to 2016 Change				2014 to 2015 Change
	(Dollars in thousands)
Research and development	$	77,926	$	42,559	$	21,824	$	35,367	83	%	$	20,735	95	%
Sales and marketing		65,267		49,308		33,322		15,959	32	%		15,986	48	%
General and administrative		51,077		35,991		18,960		15,086	42	%		17,031	90	%
Charitable contribution		3,860		—		—		3,860	100	%		—	—

Total operating expenses	$	198,130	$	127,858	$	74,106	$	70,272	55	%	$	53,752	73	%

In 2016, research and development expenses increased by $35.4 million, or 83%, compared to 2015. The increase was primarily attributable to a $27.3 million increase in personnel costs, net of a $4.4 million increase in capitalized software development costs, largely as a result of a 61% average increase of our research and development headcount, as we continued to focus on enhancing our existing products and introducing new products, as well as enhancing product management and other technical functions. The increase was also due in part to a $1.9 million increase related to the facilities rent expense in connection with our new office lease in San Francisco, California, a $1.7 million increase in cloud infrastructure fees to support the staging and development of our products, a $1.2 million increase in amortization expense related to our internal-use software and the intangible assets acquired through business combinations and a $1.2 million increase in the software subscription expense. These increases were partially offset by a $0.8 million decrease in compensation expense related to the 2015 Repurchase, which was not incurred in 2016.

In 2016, sales and marketing expenses increased by $16.0 million, or 32%, compared to 2015. The increase was primarily attributable to a $9.4 million increase in personnel costs, largely as a result of a 35% average increase in sales and marketing headcount as we continued to expand our sales efforts in the United States and internationally, a $1.6 million increase in credit card processing fees due to increased volumes, a $0.8 million increase in the software subscription expense, a $0.8 million increase in the facilities rent expense primarily due to our new office lease in San Francisco, California, a $0.7 million increase related to our SIGNAL developer conferences, a $0.6 million increase in advertising expenses, a $0.6 million increase in professional services fees and a $0.6 million increase in employee travel expenses.

In 2016, general and administrative expenses increased by $15.1 million, or 42%, compared to 2015. The increase was primarily attributable to a $7.7 million increase in personnel costs, largely as a result of a 41% average increase in general and administrative headcount to support the growth of our business and becoming a publicly-traded company, a $4.9 million increase in sales and other taxes, a $1.4 million increase in depreciation, amortization and facilities rent primarily due to our new office lease in San Francisco, California and a $0.9 million increase in professional service fees unrelated to business combinations. These increases were partially offset by a $1.1 million decrease in compensation expense related to the 2015 Repurchase, which was not incurred in 2016, a $0.8 million decrease related to the partial reversal of previously recorded tax liability upon settlement of the obligation and a $0.7 million decrease in professional services fees related to business combinations.

In 2016, of the net proceeds we received in our follow-on public offering, $3.9 million was reserved to fund and support the operations of Twilio.org. In December 2016, Twilio.org donated the full $3.9 million proceeds into an independent Donor Advised Find to further our philanthropic goals.

In 2015, research and development expenses increased by $20.7 million, or 95%, compared to 2014. The increase was primarily attributable to a $14.0 million increase in personnel costs, net of a $4.7 million increase in capitalized software development costs, largely as a result of a 80% increase of our research and development headcount, as we continued to focus on enhancing our existing products and introducing new products, as well as enhancing product management and other technical functions. The increase was also due in part to a $1.1 million increase in cloud infrastructure fees to support the staging and development of our products, a $1.0 million increase in outsourced engineering services, net of $0.8 million increase in capitalized software development costs, a $0.8 million increase in compensation expense in relation to the 2015 Repurchase, a $0.8 million increase in amortization expense related to our internal-use software and the intangible assets acquired in the Authy transaction, a $0.7 million increase related to amortization of prepaid software licenses and a $0.5 million increase in our general overhead costs.

In 2015, sales and marketing expenses increased by $16.0 million, or 48%, compared to 2014. The increase was primarily attributable to a $9.6 million increase in personnel costs, largely as a result of a 39% increase in sales and marketing headcount as we continued to expand our sales efforts in the United States and internationally, a $2.6 million increase related to our SIGNAL developer conference, which was not held in the prior year, a $1.9 million increase in advertising expenses, a $0.7 million increase in credit card processing fees and a $0.2 million increase in our general overhead costs. These increases were partially offset by a $0.5 million decrease in expenses for brand awareness programs and events other than our SIGNAL developer conference.

In 2015, general and administrative expenses increased by $17.0 million, or 90%, compared to 2014. The increase was primarily attributable to a $7.5 million increase in personnel costs, largely as a result of a 72% increase in general and administrative headcount to support the growth of our business, a $4.1 million increase in professional service fees unrelated to Authy, a $2.0 million increase in sales and other taxes, a $1.1 million increase in compensation expense related to the 2015 Repurchase, a $0.8 million increase in professional service fees related to the acquisition of Authy and a $0.7 million increase related to depreciation, amortization and other general overhead, all associated with the growth of our business.

The following tables set forth our unaudited quarterly statements of operations data for each of the eight quarters ended December 31, 2016, as well as the percentage that each line item represents of our revenue for each quarter presented. The information for each quarter has been prepared on a basis consistent with our audited consolidated financial statements included in this Annual Report on Form 10-K, and reflect, in the opinion of management, all adjustments of a normal, recurring nature that are necessary for a fair presentation of the financial information contained in those statements. Our historical results are not necessarily indicative of the results that may be expected in the future. The following quarterly financial data should be read in conjunction with our audited consolidated financial statements included in this Annual Report on Form 10-K.

	Three Months Ended

	March 31, 2015			June 30, 2015			Sept. 30, 2015			Dec. 31, 2015			March 31, 2016			June 30, 2016			Sept. 30, 2016			Dec. 31, 2016
	(Unaudited, in thousands)
Consolidated Statements of Operations:
Revenue	$	33,365		$	37,954		$	44,262		$	51,338		$	59,340		$	64,510		$	71,533		$	81,952
Cost of revenue⁽¹⁾⁽²⁾		15,545			16,827			19,602			22,480			26,827			28,203			31,285			34,205

Gross profit		17,820			21,127			24,660			28,858			32,513			36,307			40,248			47,747

Operating expenses:
Research and development⁽¹⁾⁽²⁾		8,480			9,388			11,602			13,089			14,864			17,369			21,106			24,587
Sales and marketing⁽¹⁾		9,869			14,164			12,067			13,208			13,422			18,156			15,873			17,816
General and administrative⁽¹⁾⁽²⁾		8,265			7,035			9,935			10,756			10,593			11,635			14,545			14,304
Charitable contribution		—			—			—			—			—			—			—			3,860

Total operating expenses		26,614			30,587			33,604			37,053			38,879			47,160			51,524			60,567

Loss from operations		(8,794	)		(9,460	)		(8,944	)		(8,195	)		(6,366	)		(10,853	)		(11,276	)		(12,820	)
Other income (expense), net		53			(83	)		(28	)		69			(18	)		(28	)		138			225

Loss before (provision) benefit for income taxes		(8,741	)		(9,543	)		(8,972	)		(8,126	)		(6,384	)		(10,881	)		(11,138	)		(12,595	)
(Provision) benefit for income taxes		81			(33	)		(36	)		(134	)		(84	)		(113	)		(116	)		(13	)

Net loss		(8,660	)		(9,576	)		(9,008	)		(8,260	)		(6,468	)		(10,994	)		(11,254	)		(12,608	)
Deemed dividend to investors in relation to tender offer		—			—			(3,392	)		—			—			—			—			—

Net loss attributable to common stockholders	$	(8,660	)	$	(9,576	)	$	(12,400	)	$	(8,260	)	$	(6,468	)	$	(10,994	)	$	(11,254	)	$	(12,608	)

	Three Months Ended

	March 31, 2015		June 30, 2015		Sept. 30, 2015		Dec. 31, 2015		March 31, 2016		June 30, 2016		Sept. 30, 2016		Dec. 31, 2016
	(Unaudited, in thousands)
Cost of revenue	$	14	$	14	$	17	$	20	$	23	$	28	$	84	$	156
Research and development		663		796		980		1,607		1,516		2,379		3,741		5,310
Sales and marketing		420		513		691		765		734		1,116		1,432		1,690
General and administrative		548		599		553		677		752		1,453		2,391		1,420

Total	$	1,645	$	1,922	$	2,241	$	3,069	$	3,025	$	4,976	$	7,648	$	8,576

	Three Months Ended

	March 31, 2015		June 30, 2015		Sept. 30, 2015		Dec. 31, 2015			March 31, 2016		June 30, 2016		Sept. 30, 2016		Dec. 31, 2016
	(Unaudited, in thousands)
Cost of revenue	$	28	$	21	$	70	$	120		$	70	$	70	$	70	$	409
Research and development		17		87		38		(12	)		38		38		38		37
General and administrative		11		28		27		29			27		28		28		27

Total	$	56	$	136	$	135	$	137		$	135	$	136	$	136	$	473

	Three Months Ended

	March 31, 2015			June 30, 2015			Sept. 30, 2015			Dec. 31, 2015			March 31, 2016			June 30, 2016			Sept. 30, 2016			Dec. 31, 2016
	(Unaudited)
Consolidated Statements of Operations, as a percentage of revenue:**
Revenue		100	%		100	%		100	%		100	%		100	%		100	%		100	%		100	%
Cost of revenue		47			44			44			44			45			44			44			42

Gross margin		53			56			56			56			55			56			56			58

Operating expenses:
Research and development		25			25			26			25			25			27			30			30
Sales and marketing		30			37			27			26			23			28			22			22
General and administrative		25			19			22			21			18			18			20			17
Charitable contribution		—			—			—			—			—			—			—			5

Total operating expenses		80			81			76			72			66			73			72			74

Loss from operations		(26	)		(25	)		(20	)		(16	)		(11	)		(17	)		(16	)		(16	)
Other income (expense), net		*			*			*			*			*			*			*			*

Loss before (provision) benefit for income taxes		(26	)		(25	)		(20	)		(16	)		(11	)		(17	)		(16	)		(15	)
(Provision) benefit for income taxes		*			*			*			*			*			*			*			*

Net loss		(26	)		(25	)		(20	)		(16	)		(11	)		(17	)		(16	)		(15	)
Deemed dividend to investors in relation to tender offer		—			—			(8	)		—			—			—			—			—

Net loss attributable to common stockholders		(26	)%		(25	)%		(28	)%		(16	)%		(11	)%		(17	)%		(16	)%		(15	)%

	Three Months Ended

	March 31, 2015			June 30, 2015			Sept. 30, 2015			Dec. 31, 2015			March 31, 2016			June 30, 2016			Sept. 30, 2016			Dec. 31, 2016
	(Unaudited, dollars in thousands)
Number of Active Customer Accounts (as of end date of period)⁽¹⁾		19,340			21,226			23,822			25,347			28,648			30,780			34,457			36,606
Base Revenue (in thousands)⁽²⁾	$	25,931		$	30,694		$	36,729		$	43,497		$	49,834		$	56,370		$	64,099		$	75,245
Base Revenue Growth Rate		70	%		75	%		77	%		97	%		92	%		84	%		75	%		73	%
Dollar-Based Net Expansion Rate⁽³⁾		145	%		149	%		156	%		172	%		170	%		164	%		155	%		155	%

Our quarterly revenue increased in each period presented primarily due to an increase in the usage of products as well as the adoption of additional products by our existing customers as evidenced by our Dollar-Based Net Expansion Rates, and an increase in our new customers. Our gross margin improved starting with the second quarter of 2015 due to continued platform optimization, and further improved in the fourth quarter of 2016 primarily as a result of cost savings from our continued platform optimization efforts, along with changes in our product and geographic mix.

Our operating expenses have increased sequentially in absolute dollars as a result of our growth, primarily related to increased personnel costs to support our expanded operations and our continued investment in our products. The 2015 Repurchase resulted in $0.8 million and $1.1 million of research and development expense and general and administrative expense, respectively, in the third quarter of 2015. The sales and marketing expenses included $2.6 million and $3.0 million of expenses related to our SIGNAL developer conference in the second quarter of 2015 and 2016, respectively. The general and administrative expenses in the first quarter of 2015 included $1.1 million of professional service fees related to the acquisition of Authy. In addition, the general and administrative expenses for the quarters presented include a significant amount of sales and other taxes to which we are subject. We have not historically collected these taxes from our customers, but we expect to do so in the future.

To date, our principal sources of liquidity have been the net proceeds of $155.5 million and $64.4 million, after deducting underwriting discounts and offering expenses paid or payable by us, from our initial public offering in June 2016 and our follow-on public offering in October 2016, respectively; the net proceeds we received through private sales of equity securities, as well as the payments received from customers using our products. From our inception through March 31, 2016, we completed several rounds of equity financing through the sale of our convertible preferred stock for total net proceeds of $237.1 million. We believe that our cash and cash equivalents balances, our credit facility and the cash flows generated by our operations will be sufficient to satisfy our anticipated cash needs for working capital and capital expenditures for at least the next 12 months. However, our belief may prove to be incorrect, and we could utilize our available financial resources sooner than we currently expect. Our future capital requirements and the adequacy of available funds will depend on many factors, including

those set forth in the section titled "Risk Factors." We cannot assure you that we will be able to raise additional capital on acceptable terms or at all.

On March 19, 2015, we entered into a $15.0 million revolving line of credit with Silicon Valley Bank. Under this credit facility, outstanding borrowings are based on our prior month's monthly recurring revenue. Advances on the line of credit bear interest payable monthly at Wall Street Journal prime rate plus 1%. Borrowings are secured by substantially all of our assets, with limited exceptions. In order to be able to borrow against the credit line, we must comply with certain restrictive covenants. We are currently in compliance with these covenants. This credit facility expires in March 2017. As of December 31, 2016, the total amount available to be borrowed by us was $15.0 million and we had no outstanding balance on this credit facility.

	Year Ended December 31,

	2016			2015			2014
Cash provided by (used in) operating activities	$	10,091		$	(18,762	)	$	(17,360	)
Cash used in investing activities		(42,425	)		(12,379	)		(5,340	)
Cash provided by financing activities		229,164			107,349			612

Net increase (decrease) in cash and cash equivalents	$	196,830		$	76,208		$	(22,088	)

In 2016, cash provided by operating activities consisted primarily of our net loss of $41.3 million adjusted for non-cash items, including $24.2 million of stock-based compensation expense, $8.3 million of depreciation and amortization expense and $16.9 million of cumulative changes in operating assets and liabilities. With respect to changes in operating assets and liabilities, accounts payable and other liabilities increased $25.9 million and deferred revenue increased $4.1 million, which were primarily due to increases in transaction volumes and additional accruals of sales and other taxes. Other long-term liabilities increased $9.1 million, primarily due to the increase in the deferred rent balance related to our new office lease in San Francisco, California. This was partially offset by an increase in accounts receivable and prepaid expenses of $22.0 million, which primarily resulted from the growth of our business and the timing of cash receipts from certain of our larger customers, pre-payments for cloud infrastructure fees and certain operating expenses, and a $5.7 million net increase related to the tenant improvement allowance under our new San Francisco, California office lease, after collecting $2.6 million from the landlord in the fourth quarter of 2016.

In 2015, cash used in operating activities consisted primarily of our net loss of $35.5 million adjusted for non-cash items, including $8.9 million of stock-based compensation expense, $4.2 million of depreciation and amortization expense and $2.9 million of cumulative changes in operating assets and liabilities. With respect to changes in operating assets and liabilities, accounts payable and other liabilities increased $13.9 million and deferred revenue increased $2.0 million, which were primarily due to increases in transaction volumes and additional accruals of sales and other taxes. This was partially offset by an increase in accounts receivable and prepaid expenses of $12.6 million, which primarily resulted from the growth of our business and the timing of cash receipts from certain of our larger customers, as well as pre-payments for cloud infrastructure fees and certain operating expenses.

In 2014, cash used in operating activities consisted primarily of our net loss of $26.8 million adjusted for certain non-cash items, including $4.0 million of stock-based compensation expense and $1.8 million of depreciation and amortization, as well as $3.4 million of cumulative changes in operating assets and liabilities. With respect to changes in assets and liabilities, accounts payable and other liabilities increased $8.6 million and deferred revenue increased $1.6 million, which was primarily due to increases in transaction volumes in 2014 compared to 2013 and additional accruals of sales and other taxes. This was partially offset by an increase in accounts receivable and prepaid expenses of $7.2 million, which primarily resulted from the growth of our business and the timing of cash receipts from certain of our large customers, as well as pre-payments for cloud infrastructure fees and certain operating expenses.

In 2016, cash used in investing activities was $42.4 million, primarily consisting of $14.2 million of payments related to purchases of property and equipment as we continued to expand our offices and grow our headcount to support the growth of our business, $11.5 million of payments for capitalized software development as we continued to build new products and enhance our existing products, an $8.5 million payment related to the Kurento WebRTC acquisition and a $7.4 million increase in restricted cash related to our new office lease in San Francisco, California.

In 2015, cash used in investing activities was $12.4 million, primarily consisting of $8.4 million of payments for capitalized software development as we continued to build new products and enhance our existing products, $1.8 million of payments related to the acquisition of Authy, net of $1.2 million of cash acquired, and $1.7 million of payments related to purchases of property and equipment as we continued to expand our offices and grow our headcount to support the growth of our business.

In 2014, cash used in investing activities was $5.3 million, primarily consisting of $3.6 million of payments for capitalized software development as we continued to build new products and enhance our existing products, $1.0 million of payments for purchases of property and equipment as we continued to expand our offices and grow our headcount to support the growth of our business and $0.5 million of payments for patent development.

In 2016, cash provided by financing activities was $229.2 million, primarily consisting of $225.7 million of aggregate proceeds raised in our initial public offering and follow-on public offering, net of underwriting discounts, and $9.1 million of proceeds from stock options exercises by our employees. These cash inflows were partially offset by $4.6 million of costs paid in connection with our public offerings.

In 2015, cash provided by financing activities was $107.3 million, primarily consisting of $125.4 million proceeds from our sales of Series E convertible preferred stock, net of issuance expenses, and $3.4 million proceeds from stock option exercises by our employees. This was partially offset by the $20.8 million of payments made in connection with our 2015 Repurchase and $0.7 million of payments for deferred offering costs.

In 2014, cash provided by financing activities was $0.6 million, primarily consisting of proceeds from stock option exercises by our employees.

We have not entered into any off-balance sheet arrangements and do not have any holdings in variable interest entities.

The following table summarizes our non-cancelable contractual obligations as of December 31, 2016:


ý		ANNUAL REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT 1934
For the fiscal year ended December 31, 2016
or
o		TRANSITION REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934
For the transition period from to

Title of each class		(Name of each exchange on which registered)

Class A Common Stock, par value $0.001 per share		The New York Stock Exchange


Large accelerated filer o		Accelerated filer o		Non-accelerated filer ý (Do not check if a smaller reporting company)		Smaller reporting company o



PART I
Item 1.	Business	5
Item 1A.	Risk Factors	19
Item 1B.	Unresolved Staff Comments	51
Item 2.	Properties	51
Item 3.	Legal Proceedings	51
Item 4.	Mine Safety Disclosures	52
PART II
Item 5.	Market for Registrant's Common Equity, Related Stockholder Matters and Issuer Purchases of Equity Securities	53
Item 6.	Selected Financial Data	56
Item 7.	Management's Discussion and Analysis of Financial Condition and Results of Operations	60
Item 7A.	Quantitative and Qualitative Disclosures About Market Risk	82
Item 8.	Financial Statements and Supplementary Data	83
Item 9.	Changes in and Disagreements with Accountants on Accounting and Financial Disclosure	125
Item 9A.	Controls and Procedures	125
Item 9B.	Other Information	125
PART III
Item 10.	Directors, Executive Officers and Corporate Governance	126
Item 11.	Executive Compensation	126
Item 12.	Security Ownership of Certain Beneficial Owners and Management and Related Stockholder Matters	126
Item 13.	Certain Relationships and Related Transactions and Director Independence	126
Item 14.	Principal Accountant Fees and Services	126
PART IV
Item 15.	Exhibits, Financial Statement Schedules	126
Item 16.	Form 10-K Summary	126

	Low		High

Fiscal Year 2016
Second Quarter (from June 23, 2016)	$	23.66	$	41.89
Third Quarter	$	33.07	$	70.96
Fourth Quarter	$	28.37	$	66.64


Delaware (State or other jurisdiction of incorporation or organization)		26-2574840 (I.R.S. Employer Identification Number)

	Less Than 1 Year		1 to 3 Years		3 to 5 Years		5 Years or More		Total

	(In thousands)
As of December 31, 2016:
Operating leases⁽¹⁾	$	7,534	$	14,144	$	14,070	$	16,052	$	51,800
Purchase obligations⁽²⁾		19,034		42,871		91		—		61,996

Total	$	26,568	$	57,015	$	14,161	$	16,052	$	113,796