diff --git a/packages/config/src/chainConfig/presets/mainnet.ts b/packages/config/src/chainConfig/presets/mainnet.ts
index 46c278679e9c..3611c5fbb810 100644
--- a/packages/config/src/chainConfig/presets/mainnet.ts
+++ b/packages/config/src/chainConfig/presets/mainnet.ts
@@ -7,8 +7,8 @@ export const chainConfig: IChainConfig = {
   PRESET_BASE: PresetName.mainnet,
 
   // Transition
-  // TBD, 2**256-1 is a placeholder
-  TERMINAL_TOTAL_DIFFICULTY: BigInt("115792089237316195423570985008687907853269984665640564039457584007913129639935"),
+  // Estimated: Sept 15, 2022
+  TERMINAL_TOTAL_DIFFICULTY: BigInt("58750000000000000000000"),
   TERMINAL_BLOCK_HASH: b("0x0000000000000000000000000000000000000000000000000000000000000000"),
   TERMINAL_BLOCK_HASH_ACTIVATION_EPOCH: Infinity,
 
@@ -29,12 +29,12 @@ export const chainConfig: IChainConfig = {
   //  - These may be re-assigned to another fork-version later
   //  - Temporarily set to max uint64 value: 2**64 - 1
 
-  // Altair
+  // Altair - Oct 27, 2021, 10:56:23am UTC
   ALTAIR_FORK_VERSION: b("0x01000000"),
-  ALTAIR_FORK_EPOCH: 74240, // Oct 27, 2021, 10:56:23am UTC
-  // Bellatrix
+  ALTAIR_FORK_EPOCH: 74240,
+  // Bellatrix - Sept 6, 2022, 11:34:47am UTC
   BELLATRIX_FORK_VERSION: b("0x02000000"),
-  BELLATRIX_FORK_EPOCH: Infinity,
+  BELLATRIX_FORK_EPOCH: 144896,
   // Sharding
   SHARDING_FORK_VERSION: b("0x03000000"),
   SHARDING_FORK_EPOCH: Infinity,