Classification of short-term investments as of December 31, 2024 and 2025 were shown as below:

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The gross unrecognized holding gains or losses on the time deposits and held-to-maturity debt securities were nil as of December 31, 2024 and 2025.

The costs of equity securities were RMB35,737,847 and RMB47,244,735 (US$6,755,908), with net unrealized gains of RMB8,741,557 and RMB18,788,861 (US$2,686,771) as of December 31, 2024 and 2025, respectively.

For the years ended December 31, 2023, 2024 and 2025, interest income related to time deposits and held-to-maturity debt securities were RMB5,750,934, RMB7,314,780 and RMB7,913,608 (US$1,131,631), respectively.

As of December 31, 2024 and 2025, available-for-sale debt securities include government bonds purchased from financial institutions with maturities within one year. The following table summarizes the details of available-for-sale debt securities:

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Other debt investments mainly include loan investments, as of December 31, 2024 and 2025, the carrying amounts for the loan investments, net of allowance for credit losses, were RMB12,119,285 and RMB6,856,643 (US$980,487).

The Group enters into lending agreements with certain financial institutions, under which it lends certain held-to-maturity debt securities to the counterparty. As of December 31, 2024 and 2025, the carrying amount of the securities lent was nil and RMB14,649,111 (US$2,094,795), respectively, with collateral received amounted nil and RMB155,635 (US$22,256), respectively.