Starknet, in its upcoming updates, is poised for some major shifts. Here's a breakdown:

### V0.12.3:

- Feeder Gateway Deprecation: This is a significant change urging builders to migrate to an API service or run independent full nodes.

- Account Contract Validation Updates: Detailed changes are available in the release notes.

### V0.13.0:

- New Transaction Type (V3): Sets the stage for future features like STRK fee payments, fee market, paymaster, and nonce generalization. More details in SNIP-8 and SNIP-10.

- Cairo Version 2.4.0: Brings string literals and basic string operations.

Upgrade Schedule:

- Nov 19, 2023: V0.12.3 Goerli testnet

- Dec 11, 2023: V0.12.3 mainnet (moved a week earlier)

- Dec 5, 2023: V0.13.0 Goerli testnet (might be delayed to Dec 13 if necessary)

- Jan 22, 2024: V0.13.0 mainnet (subject to governance vote)

Sepolia Testnet Migration:

- Goerli Deprecation: Starknet will transition to Sepolia post the Goerli deprecation, urging developers to move to Sepolia once feasible.

- Migration Start: Nov 15, 2023, marking the migration of nodes, services, SDKs, and dev tools to Sepolia.

- Support & Clean State: Sepolia supports Cairo v0 and Cairo v2.0.0 and higher with a fresh start.

Developers are encouraged to ask questions or voice concerns in the community forum.