[UPGRADE] Mainnet upgrade to v.1.6.0

[AkKoks]

Proposal

Network: tacchain_239-1
Current version: v1.0.4
Target version: v1.6.0
Upgrade name: v1.6.0

Overview

This proposal upgrades the TacChain mainnet from v1.0.4 to v1.6.0.

The upgrade replaces the legacy evmos-based EVM stack with upstream cosmos/evm v0.6.0, upgrades Cosmos SDK from v0.50.15 to v0.53.6, and applies the TacBuild-specific migration handler required to preserve the existing EVM and staking state. It also corrects the x/mint blocks_per_year parameter so that real token emission matches the nominal inflation rate (see "Mint Inflation Correction" below).

References:

• Changelog: https://github.com/TacBuild/tacchain/blob/main/docs/CHANGELOG-v104-v160.md
• Migration guide: https://github.com/TacBuild/tacchain/blob/main/docs/migration-v104-v160.md

Release Artifacts

Artifact	Value
Git tag	v1.6.0
Commit	ab311af
GitHub release	v1.6.0

Upgrade Timeline

Dates and block numbers are approximate and will be finalized before proposal submission.

This is an expedited proposal: the voting period is 3.5 days (302400s) with a 66.7% expedited threshold and a 50000000000000000utac (0.05 TAC) minimum deposit.

Event	Date (UTC)	Block
Governance proposal submitted	June 26, 2026, 12:00 UTC	-
Voting period ends (expedited, +3.5 days)	June 30, 2026, 00:00 UTC	-
Upgrade activation height	~ June 30, 2026, 12:00 UTC	21,776,800
Node update deadline	after upgrade height	-

Updating Process

Validators should vote on the proposal during the voting period and prepare their nodes before the upgrade height.

At the upgrade height the chain will halt with the upgrade name v1.6.0. After the halt:

1. Stop tacchaind.
2. Back up the node home directory.
3. Replace the binary with the v1.6.0 binary.
4. Update app.toml.
5. Start tacchaind.

The upgrade handler runs automatically on the first block after restart. No manual state migration is required.

Local rehearsals have been run for the v1.0.4 -> v1.6.0 upgrade path, including EVM params migration, historical governance EVM-params proposal migration, EVM contract storage preservation, post-upgrade EVM writes, staking state normalization, vesting rescue edge cases, and the x/mint blocks_per_year correction.

Mandatory app.toml Change

Validators must set the EVM chain ID explicitly in app.toml.

For mainnet:

[evm]
evm-chain-id = 239

This value is mandatory. If evm-chain-id is absent or set to 0, the node may fall back to an incorrect upstream default (262144). That would break EIP-155 replay protection, eth_chainId, and EVM transaction signing.

Also remove the old JSON-RPC field if it is present:

[json-rpc]
# remove this line if present
fix-revert-gas-refund-height = 0

See the migration guide for all new app.toml fields:

https://github.com/TacBuild/tacchain/blob/main/docs/migration-v104-v160.md

Technical Implementation

The proposed upgrade includes the following major changes.

EVM Stack Upgrade

• Replaces the evmos-based cosmos/evm v0.2.0 stack with upstream cosmos/evm v0.6.0.
• Upgrades go-ethereum from the legacy v1.10 series to v1.16.
• Adds support for newer EVM functionality, including EIP-7702, EIP-2935, state overrides in eth_call, and new debug / access-list RPC methods.
• Moves allow_unprotected_txs from consensus params to local JSON-RPC config.
• Removes chain_config from x/vm params.

Cosmos SDK Upgrade

• Upgrades Cosmos SDK from v0.50.15 to v0.53.6.
• Removes deprecated x/params and x/crisis app wiring.
• Removes the unused feeibc store.

Upgrade Handler

The v1.6.0 upgrade handler performs the on-chain state migration:

• Migrates x/vm params from the old proto layout to the new cosmos/evm v0.6.0 layout.
• Migrates historical x/gov proposals that embed legacy x/vm MsgUpdateParams payloads, so governance queries remain decodable after the EVM proto field numbers change.
• Initializes the new EVM coin info KV entry for utac.
• Migrates x/erc20 params and precompile KV records.
• Preserves EVM JSON-RPC chain ID semantics for mainnet (239).
• Rebuilds staking LSM accounting to normalize staking state after historical validator slashing edge cases.
• Migrates the vesting rescue account state according to the embedded rescue plan.
• Corrects the x/mint blocks_per_year parameter (see "Mint Inflation Correction").

Mint Inflation Correction

The x/mint blocks_per_year parameter was originally set to 15,768,000, which assumes a 2.0s block time (365 × 86400 / 2.0). The mint module mints exactly annual_provisions / blocks_per_year per block, independent of wall-clock time. Mainnet's real block time is ~1.553s, so the chain has been minting materially more tokens per year than the nominal inflation rate implies (actual emission ≈ nominal × 2.0 / block_time, i.e. roughly +28–42% over the reported inflation rate).

The upgrade handler sets blocks_per_year to 20,300,000 (≈ 365 × 86400 / 1.553), which re-aligns real per-block emission with the nominal inflation rate. Only blocks_per_year is changed; the inflation curve (inflation_max, inflation_min, goal_bonded, inflation_rate_change) is left unchanged. The reported inflation rate figure is unaffected — this correction makes the actual emission match it.

[AkKoks]

Upgrade proposal submitted at 26 June 2026 12:00 UTC.

Proposal ID is: 6

[AkKoks]

TAC Mainnet v1.6.0 — proposal passed

Governance proposal #6 has passed. The upgrade is scheduled at block 21,776,800, expected around 12:15 UTC today.

Track the upgrade countdown live here:
https://ping.explorer.tac.build/tacchain/block/21776800
(Give it 10-20 seconds to settle — the ETA is based on a rolling average block time.)

Reminder: have the v1.6.0 binary ready and set evm-chain-id = 239 in app.toml before restarting after the halt.