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# T4 Network Upgrade

This page summarizes T4 scope.

:::info[T4 status]
T4 is active on both testnet and mainnet.
:::

## Timeline

| Network | Date | Timestamp |
|---------|------|-----------|
| Testnet | May 14, 2026 4pm CEST | `1778767200` |
| Mainnet | May 18, 2026 4pm CEST | `1779112800` |

Node operators needed to upgrade to the T4-compatible release (v1.7.0, released May 11, 2026 4pm CEST) before the testnet activation timestamp.

## Overview

T4 introduced the following changes:

* [Consensus context in block headers](https://tips.sh/1031) to unlock deferred verification and reduce finalization latency
* [T4 network upgrade](https://tips.sh/1046) bug fixes and security hardening

## Compatible SDK releases

| SDK | T4-compatible release |
|-----|-----------------------|
| [Rust](https://github.com/tempoxyz/tempo) | [`tempo-alloy@1.7.0`](https://github.com/tempoxyz/tempo/releases/tag/tempo-alloy%401.7.0), [`tempo-primitives@1.7.0`](https://github.com/tempoxyz/tempo/releases/tag/tempo-primitives%401.7.0), [`tempo-contracts@1.7.0`](https://github.com/tempoxyz/tempo/releases/tag/tempo-contracts%401.7.0) |
| [Foundry](https://github.com/foundry-rs/foundry) | nightly (T4 hardfork-aware decoding) |

See [Developer tools](/docs/quickstart/developer-tools) for the broader SDK ecosystem.

## Related docs

* [Network upgrades and releases](/docs/guide/node/network-upgrades)
* [Consensus context in block headers](https://tips.sh/1031)
* [T4 network upgrade](https://tips.sh/1046)

## Feature TIPs

### Consensus context in block headers

The [specification](https://tips.sh/1031) added an optional `Context` field (epoch, view, parent view, leader) as the last field of `TempoHeader`. This commits consensus metadata to the block hash so Tempo blocks implement Commonware's `CertifiableBlock` trait, enabling deferred verification (optimistic notarization with async background verification) and reduced finalization latency. Pre-T4 headers are unchanged; post-T4 headers require the field, and validators reject mismatched context.