Uber Technologies Inc. filed paperwork confidentially this week for its initial public offering, according to people familiar with the matter, as it races with smaller rival Lyft Inc. to be the first to market.

The S-1 filing with the Securities and Exchange Commission puts Uber neck-and-neck with Lyft. Both planned IPOs are shaping up to be among the biggest in a spate of offerings aimed for 2019. Lyft said Thursday it had filed its S-1, and people familiar with the matter have said it is aiming to debut in March or April.

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