The Hedera developer community and our ecosystem partners have expressed interest in early access to Hedera codebase features and functionality, prior to their release on the Hedera testnet and mainnet. In response to this feedback, we started looking into the idea of a second testnet — the "previewnet" — which would run a development version of the Hedera codebase.
The Hedera previewnet is designed to offer developers in the Hedera community early exposure to features coming down the pipe. It’s not always stable and accounts / data are likely to be lost when the network codebase is upgraded.
As of right now, you’ll need to use the latest version of the SDK in the language of your choice to interact with the previewnet. You can find all of the Hedera SDKs in our documentation, here: https://docs.hedera.com/guides/docs/sdks. We plan to support a previewnet version of the officially supported SDKs in the future, but do not have a timeline for this yet. Features in certain versions of the previewnet codebase will not be accessible through the SDK.
The source of truth for Hedera network, mirror node, and planned network upgrades for Hedera’s mainnet, testnet, and, now, previewnet, will always be available at https://status.hedera.com/