Updated answer as of 2025-05-04.
According to the Market data endpoints page, the new intervals are
| Interval | interval value |
|---|---|
| seconds | 1s |
| minutes | 1m, 3m, 5m, 15m, 30m |
| hours | 1h, 2h, 4h, 6h, 8h, 12h |
| days | 1d, 3d |
| weeks | 1w |
| months | 1M |
1-second is the new interval, as informed in the page New 1-Second Interval Feature Now Available on Spot and Margin Charts of the Binance blog, in the markets pages.