In April 2021, we entered into a purchase agreement with certain counterparties for the sale of an aggregate of $1.15 billion principal amount of convertible senior notes due in 2027 (the “2027 Notes”) in a private offering to qualified institutional buyers pursuant to Rule 144A under the Securities Act of 1933, as amended (the “Securities Act”). The 2027 Notes consisted of a $1.0 billion initial placement and an over-allotment option that provided the initial purchasers of the 2027 Notes with the option to purchase an additional $150.0 million aggregate principal amount of the 2027 Notes, which was fully exercised. The 2027 Notes were issued pursuant to an indenture dated April 30, 2021. The net proceeds from the issuance of the 2027 Notes were $1.05 billion, net of debt issuance costs and cash used to purchase the capped call transactions (“2027 Capped Call Transactions”) discussed below. The debt issuance costs are amortized to interest expense using the effective interest rate method.

The 2027 Notes are unsecured and unsubordinated obligations which do not bear regular interest and for which the principal balance will not accrete. The 2027 Notes will mature on May 1, 2027 unless repurchased, redeemed, or converted in accordance with their terms prior to such date.

The 2027 Notes are convertible into cash, shares of our Class A common stock, or a combination of cash and shares of our Class A common stock, at our election, at an initial conversion rate of 11.2042 shares of Class A common stock per $1,000 principal amount of 2027 Notes, which is equivalent to an initial conversion price of approximately $89.25 per share of our Class A common stock. The conversion rate is subject to customary adjustments for certain events as described in the indenture governing the 2027 Notes.

We may redeem for cash all or any portion of the 2027 Notes, at our option, on or after May 5, 2024 if the last reported sale price of our Class A common stock has been at least 130% of the conversion price then in effect for at least 20 trading days at a redemption price equal to 100% of the principal amount of the 2027 Notes to be redeemed, plus accrued and unpaid special interest or additional interest, if any.

Holders of the 2027 Notes may convert all or a portion of their 2027 Notes at their option prior to February 1, 2027, in multiples of $1,000 principal amounts, only under the following circumstances:

On or after February 1, 2027, the 2027 Notes are convertible at any time until the close of business on the second scheduled trading day immediately preceding the maturity date.

Holders of the 2027 Notes who convert the 2027 Notes in connection with a make-whole fundamental change, as defined in the indenture governing the 2027 Notes, or in connection with a redemption are entitled to an increase in the conversion rate. Additionally, in the event of a fundamental change, holders of the 2027 Notes may require us to repurchase all or a portion of the 2027 Notes at a price equal to 100% of the principal amount of 2027 Notes, plus any accrued and unpaid special interest, if any.

We accounted for the issuance of the 2027 Notes as a single liability measured at its amortized cost, as no other embedded features require bifurcation and recognition as derivatives.

In April 2020, we entered into the 2025 Notes in a private offering to qualified institutional buyers pursuant to Rule 144A under the Securities Act. The net proceeds from the issuance of the 2025 Notes were $888.6 million, net of debt issuance costs and cash used to purchase the capped call transactions (the “2025 Capped Call Transactions”) discussed below. The debt issuance costs are amortized to interest expense using the effective interest rate method.

The 2025 Notes are unsecured and unsubordinated obligations. Interest is payable in cash semi-annually in arrears beginning on November 1, 2020 at a rate of 0.25% per year. The 2025 Notes mature on May 1, 2025 unless repurchased, redeemed, or converted in accordance with their terms prior to such date.

The 2025 Notes are convertible into cash, shares of our Class A common stock, or a combination of cash and shares of our Class A common stock, at our election, at an initial conversion rate of 46.1233 shares of Class A common stock per $1,000 principal amount of 2025 Notes, which is equivalent to an initial conversion price of approximately $21.68 per share of our Class A common stock. We may redeem for cash all or portions of the 2025 Notes, at our option, on or after May 6, 2023 based on certain circumstances.

In August 2019, we entered into the 2026 Notes (and together with the 2027 Notes and the 2025 Notes, the “Convertible Notes”) in a private offering to qualified institutional buyers pursuant to Rule 144A under the Securities Act. The net proceeds from the issuance of the 2026 Notes were $1.15 billion, net of debt issuance costs and cash used to purchase the capped call transactions (“2026 Capped Call Transactions”) discussed below. The debt issuance costs are amortized to interest expense using the effective interest rate method.

The 2026 Notes are unsecured and unsubordinated obligations. Interest is payable in cash semi-annually in arrears beginning on February 1, 2020 at a rate of 0.75% per year. The 2026 Notes mature on August 1, 2026 unless repurchased, redeemed, or converted in accordance with the terms prior to such date.

The 2026 Notes are convertible into cash, shares of our Class A common stock, or a combination of cash and shares of our Class A common stock, at our election, at an initial conversion rate of 43.8481 shares of Class A common stock per $1,000 principal amount of 2026 Notes, which is equivalent to an initial conversion price of approximately $22.81 per share of our Class A common stock. We may redeem for cash all or portions of the 2026 Notes, at our option, on or after August 6, 2023 based on certain circumstances.

	As of December 31, 2021									As of December 31, 2020
	2027 Notes			2025 Notes			2026 Notes			2025 Notes			2026 Notes
	(in thousands)
Liability:
Principal	$	1,150,000		$	284,105		$	838,493		$	1,000,000		$	1,265,000
Unamortized debt discount and issuance costs⁽¹⁾		(11,361	)		(2,168	)		(5,982	)		(263,956	)		(325,875	)
Net carrying amount	$	1,138,639		$	281,937		$	832,511		$	736,044		$	939,125

Prior to January 1, 2021, we separated the 2025 Notes and the 2026 Notes into liability and equity components. On issuance, the carrying amount of the equity components was recorded as a debt discount and subsequently amortized to interest expense. Effective January 1, 2021, we early adopted ASU 2020-06 using the modified retrospective approach. As a result, the 2025 Notes and 2026 Notes are each accounted for as a single liability measured at its amortized cost, as no other embedded features require bifurcation and recognition as derivatives. Adoption of the new standard resulted in a decrease to accumulated deficit of $95.0 million, a decrease to additional paid-in capital of $664.0 million, and an increase to convertible senior notes, net of $569.0 million. The 2027 Notes were issued after January 1, 2021.

As of December 31, 2021, the debt issuance costs on the 2027 Notes, the 2025 Notes, and the 2026 Notes will be amortized over the remaining period of approximately 5.3 years, 3.3 years and 4.6 years, respectively.

Interest expense related to the amortization of debt issuance costs was $4.3 million for the year ended December 31, 2021. Interest expense related to the amortization of debt discount and issuance costs was $81.4 million and $17.8 million for the years ended December 31, 2020 and 2019, respectively. Contractual interest expense was $8.9 million, $11.2 million, and $3.7 million for the years ended December 31, 2021, 2020, and 2019, respectively.

As of December 31, 2021, the if-converted value of the 2025 Notes and 2026 Notes exceeded the principal amount by $332.2 million and $890.6 million, respectively. As of December 31, 2021, the if-converted value of the 2027 Notes did not exceed the principal amount. The sale price for conversion was satisfied as of December 31, 2021 for the 2025 Notes and the 2026 Notes, and as a result, the 2025 Notes and 2026 Notes will continue to be eligible for optional conversion during the first quarter of 2022. The 2027 Notes were not eligible for conversion as of December 31, 2021. No sinking fund is provided for the Convertible Notes, which means that we are not required to redeem or retire them periodically.

In connection with the pricing of the 2027 Notes, 2025 Notes, and 2026 Notes, we entered into the 2027 Capped Call Transactions, the 2025 Capped Call Transactions, and the 2026 Capped Call Transactions (collectively, the “Capped Call Transactions”), respectively, with certain counterparties at a net cost of $86.8 million, $100.0 million, and $102.1 million, respectively. The cap price of the 2027 Capped Call Transactions, the 2025 Capped Call Transactions, and the 2026 Capped Call Transaction is initially $121.02, $32.12, and $32.58 per share of our Class A common stock, respectively. All are subject to certain adjustments under the terms of the Capped Call Transactions. Conditions that cause adjustments to the initial strike price of the Capped Call Transactions mirror conditions that result in corresponding adjustments for the Convertible Notes.

The Capped Call Transactions are intended to reduce potential dilution to holders of our Class A common stock beyond the conversion prices up to the cap prices on any conversion of the Convertible Notes or offset any cash payments we are required to make in excess of the principal amount, as the case may be, with such reduction or offset subject to a cap. The cost of the Capped Call Transactions was recorded as a reduction of our additional paid-in capital in our consolidated balance sheets. The Capped Call Transactions will not be remeasured as long as they continue to meet the conditions for equity classification. As of December 31, 2021, the 2025 Capped Call Transactions and the 2026 Capped Call Transactions were in-the-money.

In 2021, we entered into various exchange agreements (collectively, the “Exchange Agreements”) with certain holders of the 2025 Notes and the 2026 Notes pursuant to which we exchanged approximately $715.9 million principal amount of the 2025 Notes and approximately $426.5 million principal amount of the 2026 Notes for aggregate consideration of approximately 52.4 million shares of Class A common stock (the “Exchange Shares”). The Exchange Shares included an additional 0.7 million shares of our Class A common stock not provided for under the original conversion terms of the 2025 Notes and the 2026 Notes to induce the holders to agree to the exchange.

The Exchange Agreements were accounted for as an induced conversion with the fair value of 0.7 million Exchange Shares, less accrued interest, recognized as an inducement expense in other income (expense), net in our consolidated statements of operations and included as an adjustment to reconcile net loss to net cash provided by (used in) operating activities in our consolidated statements of cash flows. Inducement expense recorded for the year ended December 31, 2021 was $41.5 million. The common stock consideration issued under the original terms of the 2025 Notes and 2026 Notes was accounted for under the general conversion accounting guidance with the net carrying amount of $1,132.6 million recorded in additional paid-in-capital and as a non-cash transaction excluded from cash activities on the consolidated statements of cash flows.

In July 2016, we entered into a senior unsecured revolving credit facility (“Credit Facility”) with certain lenders, some of which are affiliated with certain members of the underwriting syndicate for our Convertible Notes offerings, to fund working capital and general corporate-purpose expenditures. Since July 2016, we have amended the Credit Facility multiple times. As of December 31, 2021, the Credit Facility has a maximum borrowing amount of $1.05 billion, bears interest at LIBO plus 0.75%, as well as an annual commitment fee of 0.10% on the daily undrawn balance of the facility and terminates in August 2023. As of December 31, 2021, no amounts were outstanding under the Credit Facility. As of December 31, 2021, we had $23.9 million in the form of outstanding standby letters of credit.