diff --git a/book/src/cluster/stake-delegation-and-rewards.md b/book/src/cluster/stake-delegation-and-rewards.md
index fb2e0f03cc..952d7374ec 100644
--- a/book/src/cluster/stake-delegation-and-rewards.md
+++ b/book/src/cluster/stake-delegation-and-rewards.md
@@ -76,7 +76,7 @@ StakeState::Stake is the current delegation preference of the **staker** and con
 * `deactivated` - the epoch at which this stake was de-activated, some cool down epochs are required before the account
 
   ```text
-              is fully deactivated, and the stake available for withdrawal    
+              is fully deactivated, and the stake available for withdrawal
   ```
 
 * `authorized_staker` - the pubkey of the entity that must sign delegation, activation, and deactivation transactions
@@ -94,7 +94,7 @@ The Stakes and the RewardsPool are accounts that are owned by the same `Stake` p
 
 ### StakeInstruction::DelegateStake
 
-The Stake account is moved from Ininitialized to StakeState::Stake form. This is how stakers choose their initial delegate validator node and activate their stake account lamports. If the stake account is already StakeState::Stake \(i.e. already activated\), the stake is re-delegated The transaction must be signed by the stake's `authorized_staker`.
+The Stake account is moved from Ininitialized to StakeState::Stake form. This is how stakers choose their initial delegate validator node and activate their stake account lamports. The transaction must be signed by the stake's `authorized_staker`.  If the stake account is already StakeState::Stake \(i.e. already activated\), the stake is re-delegated.  Stakes may be re-delegated at any time, and updated stakes are reflected immediately, but only one re-delegation is permitted per epoch.
 
 * `account[0]` - RW - The StakeState::Stake instance.  `StakeState::Stake::credits_observed` is initialized to `VoteState::credits`,  `StakeState::Stake::voter_pubkey` is initialized to `account[1]`.  If this is the initial delegation of stake, `StakeState::Stake::stake` is initialized to the account's balance in lamports,  `StakeState::Stake::activated` is initialized to the current Bank epoch, and  `StakeState::Stake::deactivated` is initialized to std::u64::MAX
 * `account[1]` - R - The VoteState instance.
@@ -132,7 +132,7 @@ stake_state.credits_observed = vote_state.credits;
 
 ### StakeInstruction::Deactivate
 
-A staker may wish to withdraw from the network. To do so he must first deactivate his stake, and wait for cool down.  
+A staker may wish to withdraw from the network. To do so he must first deactivate his stake, and wait for cool down.
 The transaction must be signed by the stake's `authorized_staker`.
 
 * `account[0]` - RW - The StakeState::Stake instance that is deactivating.
@@ -229,4 +229,3 @@ Only lamports in excess of effective+activating stake may be withdrawn at any ti
 ### Lock-up
 
 Stake accounts support the notion of lock-up, wherein the stake account balance is unavailable for withdrawal until a specified time. Lock-up is specified as a slot height, i.e. the minimum slot height that must be reached by the network before the stake account balance is available for withdrawal, except to a specified custodian. This information is gathered when the stake account is created.
-
diff --git a/book/src/running-validator/validator-stake.md b/book/src/running-validator/validator-stake.md
index b977270def..7823d4913a 100644
--- a/book/src/running-validator/validator-stake.md
+++ b/book/src/running-validator/validator-stake.md
@@ -19,7 +19,7 @@ $ solana delegate-stake ~/validator-config/stake-keypair.json ~/validator-vote-k
 
 Note that stakes need to warm up, and warmup increments are applied at Epoch boundaries, so it can take an hour or more for the change to fully take effect.
 
-Stakes can be re-delegated to another node at any time with the same command:
+Stakes can be re-delegated to another node at any time with the same command, but only one re-delegation is permitted per epoch:
 
 ```bash
 $ solana delegate-stake ~/validator-config/stake-keypair.json ~/some-other-validator-vote-keypair.json
@@ -44,4 +44,3 @@ The stake will cool down, deactivate over time. While cooling down, your stake w
 Note that a stake account may only be used once, so after deactivation, use the cli's `withdraw-stake` command to recover the previously staked lamports.
 
 Be sure and redeem your credits before withdrawing all your lamports. Once the account is fully withdrawn, the account is destroyed.
-
diff --git a/programs/bpf/Cargo.lock b/programs/bpf/Cargo.lock
index cc61de70e3..3a03a06b36 100644
--- a/programs/bpf/Cargo.lock
+++ b/programs/bpf/Cargo.lock
@@ -80,7 +80,7 @@ dependencies = [
  "cfg-if 0.1.9 (registry+https://github.com/rust-lang/crates.io-index)",
  "libc 0.2.65 (registry+https://github.com/rust-lang/crates.io-index)",
  "rustc-demangle 0.1.16 (registry+https://github.com/rust-lang/crates.io-index)",
- "serde 1.0.101 (registry+https://github.com/rust-lang/crates.io-index)",
+ "serde 1.0.102 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
 [[package]]
@@ -107,7 +107,7 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 dependencies = [
  "autocfg 0.1.6 (registry+https://github.com/rust-lang/crates.io-index)",
  "byteorder 1.3.2 (registry+https://github.com/rust-lang/crates.io-index)",
- "serde 1.0.101 (registry+https://github.com/rust-lang/crates.io-index)",
+ "serde 1.0.102 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
 [[package]]
@@ -177,7 +177,7 @@ version = "0.11.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 dependencies = [
  "feature-probe 0.1.1 (registry+https://github.com/rust-lang/crates.io-index)",
- "serde 1.0.101 (registry+https://github.com/rust-lang/crates.io-index)",
+ "serde 1.0.102 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
 [[package]]
@@ -251,7 +251,7 @@ dependencies = [
  "libc 0.2.65 (registry+https://github.com/rust-lang/crates.io-index)",
  "num-integer 0.1.41 (registry+https://github.com/rust-lang/crates.io-index)",
  "num-traits 0.2.8 (registry+https://github.com/rust-lang/crates.io-index)",
- "serde 1.0.101 (registry+https://github.com/rust-lang/crates.io-index)",
+ "serde 1.0.102 (registry+https://github.com/rust-lang/crates.io-index)",
  "time 0.1.42 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
@@ -322,7 +322,7 @@ dependencies = [
  "idna 0.1.5 (registry+https://github.com/rust-lang/crates.io-index)",
  "log 0.4.8 (registry+https://github.com/rust-lang/crates.io-index)",
  "publicsuffix 1.5.3 (registry+https://github.com/rust-lang/crates.io-index)",
- "serde 1.0.101 (registry+https://github.com/rust-lang/crates.io-index)",
+ "serde 1.0.102 (registry+https://github.com/rust-lang/crates.io-index)",
  "serde_json 1.0.41 (registry+https://github.com/rust-lang/crates.io-index)",
  "time 0.1.42 (registry+https://github.com/rust-lang/crates.io-index)",
  "try_from 0.3.2 (registry+https://github.com/rust-lang/crates.io-index)",
@@ -611,7 +611,7 @@ name = "generic-array"
 version = "0.13.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 dependencies = [
- "serde 1.0.101 (registry+https://github.com/rust-lang/crates.io-index)",
+ "serde 1.0.102 (registry+https://github.com/rust-lang/crates.io-index)",
  "typenum 1.11.2 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
@@ -791,7 +791,7 @@ dependencies = [
 
 [[package]]
 name = "itertools"
-version = "0.8.0"
+version = "0.8.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 dependencies = [
  "either 1.5.3 (registry+https://github.com/rust-lang/crates.io-index)",
@@ -1359,7 +1359,7 @@ dependencies = [
  "mime 0.3.14 (registry+https://github.com/rust-lang/crates.io-index)",
  "mime_guess 2.0.1 (registry+https://github.com/rust-lang/crates.io-index)",
  "rustls 0.16.0 (registry+https://github.com/rust-lang/crates.io-index)",
- "serde 1.0.101 (registry+https://github.com/rust-lang/crates.io-index)",
+ "serde 1.0.102 (registry+https://github.com/rust-lang/crates.io-index)",
  "serde_json 1.0.41 (registry+https://github.com/rust-lang/crates.io-index)",
  "serde_urlencoded 0.5.5 (registry+https://github.com/rust-lang/crates.io-index)",
  "time 0.1.42 (registry+https://github.com/rust-lang/crates.io-index)",
@@ -1466,10 +1466,10 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 
 [[package]]
 name = "serde"
-version = "1.0.101"
+version = "1.0.102"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 dependencies = [
- "serde_derive 1.0.101 (registry+https://github.com/rust-lang/crates.io-index)",
+ "serde_derive 1.0.102 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
 [[package]]
@@ -1477,12 +1477,12 @@ name = "serde_bytes"
 version = "0.11.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 dependencies = [
- "serde 1.0.101 (registry+https://github.com/rust-lang/crates.io-index)",
+ "serde 1.0.102 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
 [[package]]
 name = "serde_derive"
-version = "1.0.101"
+version = "1.0.102"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 dependencies = [
  "proc-macro2 1.0.3 (registry+https://github.com/rust-lang/crates.io-index)",
@@ -1497,7 +1497,7 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 dependencies = [
  "itoa 0.4.4 (registry+https://github.com/rust-lang/crates.io-index)",
  "ryu 1.0.0 (registry+https://github.com/rust-lang/crates.io-index)",
- "serde 1.0.101 (registry+https://github.com/rust-lang/crates.io-index)",
+ "serde 1.0.102 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
 [[package]]
@@ -1507,7 +1507,7 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 dependencies = [
  "dtoa 0.4.4 (registry+https://github.com/rust-lang/crates.io-index)",
  "itoa 0.4.4 (registry+https://github.com/rust-lang/crates.io-index)",
- "serde 1.0.101 (registry+https://github.com/rust-lang/crates.io-index)",
+ "serde 1.0.102 (registry+https://github.com/rust-lang/crates.io-index)",
  "url 1.7.2 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
@@ -1545,165 +1545,165 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 
 [[package]]
 name = "solana-bpf-loader-api"
-version = "0.20.0"
+version = "0.21.0"
 dependencies = [
  "bincode 1.2.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "byteorder 1.3.2 (registry+https://github.com/rust-lang/crates.io-index)",
  "libc 0.2.65 (registry+https://github.com/rust-lang/crates.io-index)",
  "log 0.4.8 (registry+https://github.com/rust-lang/crates.io-index)",
- "serde 1.0.101 (registry+https://github.com/rust-lang/crates.io-index)",
- "solana-logger 0.20.0",
- "solana-sdk 0.20.0",
+ "serde 1.0.102 (registry+https://github.com/rust-lang/crates.io-index)",
+ "solana-logger 0.21.0",
+ "solana-sdk 0.21.0",
  "solana_rbpf 0.1.19 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
 [[package]]
 name = "solana-bpf-loader-program"
-version = "0.20.0"
+version = "0.21.0"
 dependencies = [
  "log 0.4.8 (registry+https://github.com/rust-lang/crates.io-index)",
- "solana-bpf-loader-api 0.20.0",
- "solana-logger 0.20.0",
- "solana-sdk 0.20.0",
+ "solana-bpf-loader-api 0.21.0",
+ "solana-logger 0.21.0",
+ "solana-sdk 0.21.0",
 ]
 
 [[package]]
 name = "solana-bpf-programs"
-version = "0.20.0"
+version = "0.21.0"
 dependencies = [
  "bincode 1.2.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "byteorder 1.3.2 (registry+https://github.com/rust-lang/crates.io-index)",
  "elf 0.0.10 (registry+https://github.com/rust-lang/crates.io-index)",
- "solana-bpf-loader-api 0.20.0",
- "solana-logger 0.20.0",
- "solana-runtime 0.20.0",
- "solana-sdk 0.20.0",
+ "solana-bpf-loader-api 0.21.0",
+ "solana-logger 0.21.0",
+ "solana-runtime 0.21.0",
+ "solana-sdk 0.21.0",
  "solana_rbpf 0.1.19 (registry+https://github.com/rust-lang/crates.io-index)",
  "walkdir 2.2.9 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
 [[package]]
 name = "solana-bpf-rust-128bit"
-version = "0.20.0"
+version = "0.21.0"
 dependencies = [
- "solana-bpf-rust-128bit-dep 0.20.0",
- "solana-sdk 0.20.0",
- "solana-sdk-bpf-test 0.20.0",
+ "solana-bpf-rust-128bit-dep 0.21.0",
+ "solana-sdk 0.21.0",
+ "solana-sdk-bpf-test 0.21.0",
 ]
 
 [[package]]
 name = "solana-bpf-rust-128bit-dep"
-version = "0.20.0"
+version = "0.21.0"
 dependencies = [
- "solana-sdk 0.20.0",
- "solana-sdk-bpf-test 0.20.0",
+ "solana-sdk 0.21.0",
+ "solana-sdk-bpf-test 0.21.0",
 ]
 
 [[package]]
 name = "solana-bpf-rust-alloc"
-version = "0.20.0"
+version = "0.21.0"
 dependencies = [
- "solana-sdk 0.20.0",
- "solana-sdk-bpf-test 0.20.0",
+ "solana-sdk 0.21.0",
+ "solana-sdk-bpf-test 0.21.0",
 ]
 
 [[package]]
 name = "solana-bpf-rust-dep-crate"
-version = "0.20.0"
+version = "0.21.0"
 dependencies = [
  "byteorder 1.3.2 (registry+https://github.com/rust-lang/crates.io-index)",
- "solana-sdk 0.20.0",
- "solana-sdk-bpf-test 0.20.0",
+ "solana-sdk 0.21.0",
+ "solana-sdk-bpf-test 0.21.0",
 ]
 
 [[package]]
 name = "solana-bpf-rust-external-spend"
-version = "0.20.0"
+version = "0.21.0"
 dependencies = [
- "solana-sdk 0.20.0",
- "solana-sdk-bpf-test 0.20.0",
+ "solana-sdk 0.21.0",
+ "solana-sdk-bpf-test 0.21.0",
 ]
 
 [[package]]
 name = "solana-bpf-rust-iter"
-version = "0.20.0"
+version = "0.21.0"
 dependencies = [
- "solana-sdk 0.20.0",
- "solana-sdk-bpf-test 0.20.0",
+ "solana-sdk 0.21.0",
+ "solana-sdk-bpf-test 0.21.0",
 ]
 
 [[package]]
 name = "solana-bpf-rust-many-args"
-version = "0.20.0"
+version = "0.21.0"
 dependencies = [
- "solana-bpf-rust-many-args-dep 0.20.0",
- "solana-sdk 0.20.0",
- "solana-sdk-bpf-test 0.20.0",
+ "solana-bpf-rust-many-args-dep 0.21.0",
+ "solana-sdk 0.21.0",
+ "solana-sdk-bpf-test 0.21.0",
 ]
 
 [[package]]
 name = "solana-bpf-rust-many-args-dep"
-version = "0.20.0"
+version = "0.21.0"
 dependencies = [
- "solana-sdk 0.20.0",
- "solana-sdk-bpf-test 0.20.0",
+ "solana-sdk 0.21.0",
+ "solana-sdk-bpf-test 0.21.0",
 ]
 
 [[package]]
 name = "solana-bpf-rust-noop"
-version = "0.20.0"
+version = "0.21.0"
 dependencies = [
- "solana-sdk 0.20.0",
- "solana-sdk-bpf-test 0.20.0",
+ "solana-sdk 0.21.0",
+ "solana-sdk-bpf-test 0.21.0",
 ]
 
 [[package]]
 name = "solana-bpf-rust-panic"
-version = "0.20.0"
+version = "0.21.0"
 dependencies = [
- "solana-sdk 0.20.0",
- "solana-sdk-bpf-test 0.20.0",
+ "solana-sdk 0.21.0",
+ "solana-sdk-bpf-test 0.21.0",
 ]
 
 [[package]]
 name = "solana-bpf-rust-param-passing"
-version = "0.20.0"
+version = "0.21.0"
 dependencies = [
- "solana-bpf-rust-param-passing-dep 0.20.0",
- "solana-sdk 0.20.0",
- "solana-sdk-bpf-test 0.20.0",
+ "solana-bpf-rust-param-passing-dep 0.21.0",
+ "solana-sdk 0.21.0",
+ "solana-sdk-bpf-test 0.21.0",
 ]
 
 [[package]]
 name = "solana-bpf-rust-param-passing-dep"
-version = "0.20.0"
+version = "0.21.0"
 dependencies = [
- "solana-sdk 0.20.0",
- "solana-sdk-bpf-test 0.20.0",
+ "solana-sdk 0.21.0",
+ "solana-sdk-bpf-test 0.21.0",
 ]
 
 [[package]]
 name = "solana-bpf-rust-sysval"
-version = "0.20.0"
+version = "0.21.0"
 dependencies = [
- "solana-sdk 0.20.0",
- "solana-sdk-bpf-test 0.20.0",
+ "solana-sdk 0.21.0",
+ "solana-sdk-bpf-test 0.21.0",
 ]
 
 [[package]]
 name = "solana-config-api"
-version = "0.20.0"
+version = "0.21.0"
 dependencies = [
  "bincode 1.2.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "log 0.4.8 (registry+https://github.com/rust-lang/crates.io-index)",
- "serde 1.0.101 (registry+https://github.com/rust-lang/crates.io-index)",
- "serde_derive 1.0.101 (registry+https://github.com/rust-lang/crates.io-index)",
- "solana-sdk 0.20.0",
+ "serde 1.0.102 (registry+https://github.com/rust-lang/crates.io-index)",
+ "serde_derive 1.0.102 (registry+https://github.com/rust-lang/crates.io-index)",
+ "solana-sdk 0.21.0",
 ]
 
 [[package]]
 name = "solana-crate-features"
-version = "0.20.0"
+version = "0.21.0"
 dependencies = [
  "backtrace 0.3.37 (registry+https://github.com/rust-lang/crates.io-index)",
  "bytes 0.4.12 (registry+https://github.com/rust-lang/crates.io-index)",
@@ -1716,7 +1716,7 @@ dependencies = [
  "rand_chacha 0.1.1 (registry+https://github.com/rust-lang/crates.io-index)",
  "regex-syntax 0.6.12 (registry+https://github.com/rust-lang/crates.io-index)",
  "reqwest 0.9.22 (registry+https://github.com/rust-lang/crates.io-index)",
- "serde 1.0.101 (registry+https://github.com/rust-lang/crates.io-index)",
+ "serde 1.0.102 (registry+https://github.com/rust-lang/crates.io-index)",
  "solana-ed25519-dalek 0.2.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "syn 0.15.44 (registry+https://github.com/rust-lang/crates.io-index)",
  "syn 1.0.5 (registry+https://github.com/rust-lang/crates.io-index)",
@@ -1733,13 +1733,13 @@ dependencies = [
  "curve25519-dalek 1.2.3 (registry+https://github.com/rust-lang/crates.io-index)",
  "failure 0.1.5 (registry+https://github.com/rust-lang/crates.io-index)",
  "rand 0.6.5 (registry+https://github.com/rust-lang/crates.io-index)",
- "serde 1.0.101 (registry+https://github.com/rust-lang/crates.io-index)",
+ "serde 1.0.102 (registry+https://github.com/rust-lang/crates.io-index)",
  "sha2 0.8.0 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
 [[package]]
 name = "solana-logger"
-version = "0.20.0"
+version = "0.21.0"
 dependencies = [
  "env_logger 0.7.1 (registry+https://github.com/rust-lang/crates.io-index)",
  "lazy_static 1.4.0 (registry+https://github.com/rust-lang/crates.io-index)",
@@ -1748,26 +1748,26 @@ dependencies = [
 
 [[package]]
 name = "solana-measure"
-version = "0.20.0"
+version = "0.21.0"
 dependencies = [
- "solana-sdk 0.20.0",
+ "solana-sdk 0.21.0",
 ]
 
 [[package]]
 name = "solana-metrics"
-version = "0.20.0"
+version = "0.21.0"
 dependencies = [
  "env_logger 0.7.1 (registry+https://github.com/rust-lang/crates.io-index)",
  "lazy_static 1.4.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "log 0.4.8 (registry+https://github.com/rust-lang/crates.io-index)",
  "reqwest 0.9.22 (registry+https://github.com/rust-lang/crates.io-index)",
- "solana-sdk 0.20.0",
+ "solana-sdk 0.21.0",
  "sys-info 0.5.8 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
 [[package]]
 name = "solana-rayon-threadlimit"
-version = "0.20.0"
+version = "0.21.0"
 dependencies = [
  "lazy_static 1.4.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "sys-info 0.5.8 (registry+https://github.com/rust-lang/crates.io-index)",
@@ -1775,14 +1775,14 @@ dependencies = [
 
 [[package]]
 name = "solana-runtime"
-version = "0.20.0"
+version = "0.21.0"
 dependencies = [
  "bincode 1.2.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "bv 0.11.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "byteorder 1.3.2 (registry+https://github.com/rust-lang/crates.io-index)",
  "fnv 1.0.6 (registry+https://github.com/rust-lang/crates.io-index)",
  "fs_extra 1.1.0 (registry+https://github.com/rust-lang/crates.io-index)",
- "itertools 0.8.0 (registry+https://github.com/rust-lang/crates.io-index)",
+ "itertools 0.8.1 (registry+https://github.com/rust-lang/crates.io-index)",
  "lazy_static 1.4.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "libc 0.2.65 (registry+https://github.com/rust-lang/crates.io-index)",
  "libloading 0.5.2 (registry+https://github.com/rust-lang/crates.io-index)",
@@ -1790,28 +1790,28 @@ dependencies = [
  "memmap 0.6.2 (registry+https://github.com/rust-lang/crates.io-index)",
  "rand 0.6.5 (registry+https://github.com/rust-lang/crates.io-index)",
  "rayon 1.2.0 (registry+https://github.com/rust-lang/crates.io-index)",
- "serde 1.0.101 (registry+https://github.com/rust-lang/crates.io-index)",
- "serde_derive 1.0.101 (registry+https://github.com/rust-lang/crates.io-index)",
+ "serde 1.0.102 (registry+https://github.com/rust-lang/crates.io-index)",
+ "serde_derive 1.0.102 (registry+https://github.com/rust-lang/crates.io-index)",
  "serde_json 1.0.41 (registry+https://github.com/rust-lang/crates.io-index)",
- "solana-bpf-loader-api 0.20.0",
- "solana-bpf-loader-program 0.20.0",
- "solana-logger 0.20.0",
- "solana-measure 0.20.0",
- "solana-metrics 0.20.0",
- "solana-rayon-threadlimit 0.20.0",
- "solana-sdk 0.20.0",
- "solana-stake-api 0.20.0",
- "solana-stake-program 0.20.0",
- "solana-storage-api 0.20.0",
- "solana-vote-api 0.20.0",
- "solana-vote-program 0.20.0",
+ "solana-bpf-loader-api 0.21.0",
+ "solana-bpf-loader-program 0.21.0",
+ "solana-logger 0.21.0",
+ "solana-measure 0.21.0",
+ "solana-metrics 0.21.0",
+ "solana-rayon-threadlimit 0.21.0",
+ "solana-sdk 0.21.0",
+ "solana-stake-api 0.21.0",
+ "solana-stake-program 0.21.0",
+ "solana-storage-api 0.21.0",
+ "solana-vote-api 0.21.0",
+ "solana-vote-program 0.21.0",
  "sys-info 0.5.8 (registry+https://github.com/rust-lang/crates.io-index)",
  "tempfile 3.1.0 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
 [[package]]
 name = "solana-sdk"
-version = "0.20.0"
+version = "0.21.0"
 dependencies = [
  "assert_matches 1.3.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "bincode 1.2.0 (registry+https://github.com/rust-lang/crates.io-index)",
@@ -1820,7 +1820,7 @@ dependencies = [
  "chrono 0.4.9 (registry+https://github.com/rust-lang/crates.io-index)",
  "generic-array 0.13.2 (registry+https://github.com/rust-lang/crates.io-index)",
  "hex 0.4.0 (registry+https://github.com/rust-lang/crates.io-index)",
- "itertools 0.8.0 (registry+https://github.com/rust-lang/crates.io-index)",
+ "itertools 0.8.1 (registry+https://github.com/rust-lang/crates.io-index)",
  "log 0.4.8 (registry+https://github.com/rust-lang/crates.io-index)",
  "memmap 0.6.2 (registry+https://github.com/rust-lang/crates.io-index)",
  "num-derive 0.3.0 (registry+https://github.com/rust-lang/crates.io-index)",
@@ -1828,52 +1828,52 @@ dependencies = [
  "rand 0.6.5 (registry+https://github.com/rust-lang/crates.io-index)",
  "rand_chacha 0.1.1 (registry+https://github.com/rust-lang/crates.io-index)",
  "rayon 1.2.0 (registry+https://github.com/rust-lang/crates.io-index)",
- "serde 1.0.101 (registry+https://github.com/rust-lang/crates.io-index)",
+ "serde 1.0.102 (registry+https://github.com/rust-lang/crates.io-index)",
  "serde_bytes 0.11.2 (registry+https://github.com/rust-lang/crates.io-index)",
- "serde_derive 1.0.101 (registry+https://github.com/rust-lang/crates.io-index)",
+ "serde_derive 1.0.102 (registry+https://github.com/rust-lang/crates.io-index)",
  "serde_json 1.0.41 (registry+https://github.com/rust-lang/crates.io-index)",
  "sha2 0.8.0 (registry+https://github.com/rust-lang/crates.io-index)",
- "solana-crate-features 0.20.0",
+ "solana-crate-features 0.21.0",
  "solana-ed25519-dalek 0.2.0 (registry+https://github.com/rust-lang/crates.io-index)",
- "solana-logger 0.20.0",
+ "solana-logger 0.21.0",
  "untrusted 0.7.0 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
 [[package]]
 name = "solana-sdk-bpf-test"
-version = "0.20.0"
+version = "0.21.0"
 
 [[package]]
 name = "solana-stake-api"
-version = "0.20.0"
+version = "0.21.0"
 dependencies = [
  "bincode 1.2.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "log 0.4.8 (registry+https://github.com/rust-lang/crates.io-index)",
  "num-derive 0.3.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "num-traits 0.2.8 (registry+https://github.com/rust-lang/crates.io-index)",
  "rand 0.6.5 (registry+https://github.com/rust-lang/crates.io-index)",
- "serde 1.0.101 (registry+https://github.com/rust-lang/crates.io-index)",
- "serde_derive 1.0.101 (registry+https://github.com/rust-lang/crates.io-index)",
- "solana-config-api 0.20.0",
- "solana-logger 0.20.0",
- "solana-metrics 0.20.0",
- "solana-sdk 0.20.0",
- "solana-vote-api 0.20.0",
+ "serde 1.0.102 (registry+https://github.com/rust-lang/crates.io-index)",
+ "serde_derive 1.0.102 (registry+https://github.com/rust-lang/crates.io-index)",
+ "solana-config-api 0.21.0",
+ "solana-logger 0.21.0",
+ "solana-metrics 0.21.0",
+ "solana-sdk 0.21.0",
+ "solana-vote-api 0.21.0",
 ]
 
 [[package]]
 name = "solana-stake-program"
-version = "0.20.0"
+version = "0.21.0"
 dependencies = [
  "log 0.4.8 (registry+https://github.com/rust-lang/crates.io-index)",
- "solana-logger 0.20.0",
- "solana-sdk 0.20.0",
- "solana-stake-api 0.20.0",
+ "solana-logger 0.21.0",
+ "solana-sdk 0.21.0",
+ "solana-stake-api 0.21.0",
 ]
 
 [[package]]
 name = "solana-storage-api"
-version = "0.20.0"
+version = "0.21.0"
 dependencies = [
  "assert_matches 1.3.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "bincode 1.2.0 (registry+https://github.com/rust-lang/crates.io-index)",
@@ -1881,35 +1881,35 @@ dependencies = [
  "num-derive 0.3.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "num-traits 0.2.8 (registry+https://github.com/rust-lang/crates.io-index)",
  "rand 0.6.5 (registry+https://github.com/rust-lang/crates.io-index)",
- "serde 1.0.101 (registry+https://github.com/rust-lang/crates.io-index)",
- "serde_derive 1.0.101 (registry+https://github.com/rust-lang/crates.io-index)",
- "solana-logger 0.20.0",
- "solana-sdk 0.20.0",
+ "serde 1.0.102 (registry+https://github.com/rust-lang/crates.io-index)",
+ "serde_derive 1.0.102 (registry+https://github.com/rust-lang/crates.io-index)",
+ "solana-logger 0.21.0",
+ "solana-sdk 0.21.0",
 ]
 
 [[package]]
 name = "solana-vote-api"
-version = "0.20.0"
+version = "0.21.0"
 dependencies = [
  "bincode 1.2.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "log 0.4.8 (registry+https://github.com/rust-lang/crates.io-index)",
  "num-derive 0.3.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "num-traits 0.2.8 (registry+https://github.com/rust-lang/crates.io-index)",
- "serde 1.0.101 (registry+https://github.com/rust-lang/crates.io-index)",
- "serde_derive 1.0.101 (registry+https://github.com/rust-lang/crates.io-index)",
- "solana-logger 0.20.0",
- "solana-metrics 0.20.0",
- "solana-sdk 0.20.0",
+ "serde 1.0.102 (registry+https://github.com/rust-lang/crates.io-index)",
+ "serde_derive 1.0.102 (registry+https://github.com/rust-lang/crates.io-index)",
+ "solana-logger 0.21.0",
+ "solana-metrics 0.21.0",
+ "solana-sdk 0.21.0",
 ]
 
 [[package]]
 name = "solana-vote-program"
-version = "0.20.0"
+version = "0.21.0"
 dependencies = [
  "log 0.4.8 (registry+https://github.com/rust-lang/crates.io-index)",
- "solana-logger 0.20.0",
- "solana-sdk 0.20.0",
- "solana-vote-api 0.20.0",
+ "solana-logger 0.21.0",
+ "solana-sdk 0.21.0",
+ "solana-vote-api 0.21.0",
 ]
 
 [[package]]
@@ -2660,7 +2660,7 @@ dependencies = [
 "checksum indexmap 1.2.0 (registry+https://github.com/rust-lang/crates.io-index)" = "a61202fbe46c4a951e9404a720a0180bcf3212c750d735cb5c4ba4dc551299f3"
 "checksum iovec 0.1.2 (registry+https://github.com/rust-lang/crates.io-index)" = "dbe6e417e7d0975db6512b90796e8ce223145ac4e33c377e4a42882a0e88bb08"
 "checksum itertools 0.7.11 (registry+https://github.com/rust-lang/crates.io-index)" = "0d47946d458e94a1b7bcabbf6521ea7c037062c81f534615abcad76e84d4970d"
-"checksum itertools 0.8.0 (registry+https://github.com/rust-lang/crates.io-index)" = "5b8467d9c1cebe26feb08c640139247fac215782d35371ade9a2136ed6085358"
+"checksum itertools 0.8.1 (registry+https://github.com/rust-lang/crates.io-index)" = "87fa75c9dea7b07be3138c49abbb83fd4bea199b5cdc76f9804458edc5da0d6e"
 "checksum itoa 0.4.4 (registry+https://github.com/rust-lang/crates.io-index)" = "501266b7edd0174f8530248f87f99c88fbe60ca4ef3dd486835b8d8d53136f7f"
 "checksum jobserver 0.1.17 (registry+https://github.com/rust-lang/crates.io-index)" = "f2b1d42ef453b30b7387e113da1c83ab1605d90c5b4e0eb8e96d016ed3b8c160"
 "checksum js-sys 0.3.27 (registry+https://github.com/rust-lang/crates.io-index)" = "1efc4f2a556c58e79c5500912e221dd826bec64ff4aabd8ce71ccef6da02d7d4"
@@ -2738,9 +2738,9 @@ dependencies = [
 "checksum sct 0.6.0 (registry+https://github.com/rust-lang/crates.io-index)" = "e3042af939fca8c3453b7af0f1c66e533a15a86169e39de2657310ade8f98d3c"
 "checksum semver 0.9.0 (registry+https://github.com/rust-lang/crates.io-index)" = "1d7eb9ef2c18661902cc47e535f9bc51b78acd254da71d375c2f6720d9a40403"
 "checksum semver-parser 0.7.0 (registry+https://github.com/rust-lang/crates.io-index)" = "388a1df253eca08550bef6c72392cfe7c30914bf41df5269b68cbd6ff8f570a3"
-"checksum serde 1.0.101 (registry+https://github.com/rust-lang/crates.io-index)" = "9796c9b7ba2ffe7a9ce53c2287dfc48080f4b2b362fcc245a259b3a7201119dd"
+"checksum serde 1.0.102 (registry+https://github.com/rust-lang/crates.io-index)" = "0c4b39bd9b0b087684013a792c59e3e07a46a01d2322518d8a1104641a0b1be0"
 "checksum serde_bytes 0.11.2 (registry+https://github.com/rust-lang/crates.io-index)" = "45af0182ff64abaeea290235eb67da3825a576c5d53e642c4d5b652e12e6effc"
-"checksum serde_derive 1.0.101 (registry+https://github.com/rust-lang/crates.io-index)" = "4b133a43a1ecd55d4086bd5b4dc6c1751c68b1bfbeba7a5040442022c7e7c02e"
+"checksum serde_derive 1.0.102 (registry+https://github.com/rust-lang/crates.io-index)" = "ca13fc1a832f793322228923fbb3aba9f3f44444898f835d31ad1b74fa0a2bf8"
 "checksum serde_json 1.0.41 (registry+https://github.com/rust-lang/crates.io-index)" = "2f72eb2a68a7dc3f9a691bfda9305a1c017a6215e5a4545c258500d2099a37c2"
 "checksum serde_urlencoded 0.5.5 (registry+https://github.com/rust-lang/crates.io-index)" = "642dd69105886af2efd227f75a520ec9b44a820d65bc133a9131f7d229fd165a"
 "checksum sha2 0.7.1 (registry+https://github.com/rust-lang/crates.io-index)" = "9eb6be24e4c23a84d7184280d2722f7f2731fcdd4a9d886efbfe4413e4847ea0"
diff --git a/programs/stake_api/src/stake_instruction.rs b/programs/stake_api/src/stake_instruction.rs
index d38676888c..551a597b83 100644
--- a/programs/stake_api/src/stake_instruction.rs
+++ b/programs/stake_api/src/stake_instruction.rs
@@ -20,6 +20,7 @@ pub enum StakeError {
     NoCreditsToRedeem,
     LockupInForce,
     AlreadyDeactivated,
+    TooSoonToRedelegate,
 }
 impl<E> DecodeError<E> for StakeError {
     fn type_of() -> &'static str {
@@ -32,6 +33,9 @@ impl std::fmt::Display for StakeError {
             StakeError::NoCreditsToRedeem => write!(f, "not enough credits to redeem"),
             StakeError::LockupInForce => write!(f, "lockup has not yet expired"),
             StakeError::AlreadyDeactivated => write!(f, "stake already deactivated"),
+            StakeError::TooSoonToRedelegate => {
+                write!(f, "only one redelegation permitted per epoch")
+            }
         }
     }
 }
diff --git a/programs/stake_api/src/stake_state.rs b/programs/stake_api/src/stake_state.rs
index 4204b073e5..84e0a8cc3c 100644
--- a/programs/stake_api/src/stake_state.rs
+++ b/programs/stake_api/src/stake_state.rs
@@ -103,7 +103,7 @@ pub struct Stake {
     pub config: Config,
     /// history of prior delegates and the epoch ranges for which
     ///  they were set, circular buffer
-    pub prior_delegates: [(Pubkey, Epoch, Epoch); MAX_PRIOR_DELEGATES],
+    pub prior_delegates: [(Pubkey, Epoch, Epoch, Slot); MAX_PRIOR_DELEGATES],
     /// next pointer
     pub prior_delegates_idx: usize,
 }
@@ -120,7 +120,7 @@ impl Default for Stake {
             activation_epoch: 0,
             deactivation_epoch: std::u64::MAX,
             config: Config::default(),
-            prior_delegates: <[(Pubkey, Epoch, Epoch); MAX_PRIOR_DELEGATES]>::default(),
+            prior_delegates: <[(Pubkey, Epoch, Epoch, Slot); MAX_PRIOR_DELEGATES]>::default(),
             prior_delegates_idx: MAX_PRIOR_DELEGATES - 1,
         }
     }
@@ -169,17 +169,6 @@ impl Stake {
         self.stake_activating_and_deactivating(epoch, history).0
     }
 
-    pub fn voter_pubkey(&self, epoch: Epoch) -> &Pubkey {
-        let prior_delegate_pubkey = &self.prior_delegates[self.prior_delegates_idx].0;
-        // next epoch from re-delegation, or no redelegations
-        if epoch > self.voter_pubkey_epoch || *prior_delegate_pubkey == Pubkey::default() {
-            &self.voter_pubkey
-        } else {
-            assert!(epoch <= self.prior_delegates[self.prior_delegates_idx].2);
-            prior_delegate_pubkey
-        }
-    }
-
     fn stake_activating_and_deactivating(
         &self,
         epoch: Epoch,
@@ -362,18 +351,26 @@ impl Stake {
         &mut self,
         voter_pubkey: &Pubkey,
         vote_state: &VoteState,
-        epoch: Epoch,
+        clock: &sysvar::clock::Clock,
     ) -> Result<(), StakeError> {
-        // remember old delegate,
-        if epoch != self.voter_pubkey_epoch {
-            self.prior_delegates_idx += 1;
-            self.prior_delegates_idx %= MAX_PRIOR_DELEGATES;
-
-            self.prior_delegates[self.prior_delegates_idx] =
-                (self.voter_pubkey, self.voter_pubkey_epoch, epoch);
+        // only one re-delegation supported per epoch
+        if self.voter_pubkey_epoch == clock.epoch {
+            return Err(StakeError::TooSoonToRedelegate);
         }
+
+        // remember prior delegate and when we switched, to support later slashing
+        self.prior_delegates_idx += 1;
+        self.prior_delegates_idx %= MAX_PRIOR_DELEGATES;
+
+        self.prior_delegates[self.prior_delegates_idx] = (
+            self.voter_pubkey,
+            self.voter_pubkey_epoch,
+            clock.epoch,
+            clock.slot,
+        );
+
         self.voter_pubkey = *voter_pubkey;
-        self.voter_pubkey_epoch = epoch;
+        self.voter_pubkey_epoch = clock.epoch;
         self.credits_observed = vote_state.credits();
         Ok(())
     }
@@ -500,11 +497,7 @@ impl<'a> StakeAccount for KeyedAccount<'a> {
             self.set_state(&StakeState::Stake(authorized, lockup, stake))
         } else if let StakeState::Stake(authorized, lockup, mut stake) = self.state()? {
             authorized.check(signers, StakeAuthorize::Staker)?;
-            stake.redelegate(
-                vote_account.unsigned_key(),
-                &vote_account.state()?,
-                clock.epoch,
-            )?;
+            stake.redelegate(vote_account.unsigned_key(), &vote_account.state()?, &clock)?;
             self.set_state(&StakeState::Stake(authorized, lockup, stake))
         } else {
             Err(InstructionError::InvalidAccountData)
@@ -711,7 +704,7 @@ mod tests {
 
     #[test]
     fn test_stake_delegate_stake() {
-        let clock = sysvar::clock::Clock {
+        let mut clock = sysvar::clock::Clock {
             epoch: 1,
             ..sysvar::clock::Clock::default()
         };
@@ -792,12 +785,18 @@ mod tests {
                 ..Stake::default()
             }
         );
+        // verify that delegate_stake can be called twice, 2nd is redelegate
+        assert_eq!(
+            stake_keyed_account.delegate_stake(
+                &vote_keyed_account,
+                &clock,
+                &Config::default(),
+                &signers
+            ),
+            Err(StakeError::TooSoonToRedelegate.into())
+        );
 
-        // verify that voter_pubkey() is right for all epochs, even ones that don't count (like 0)
-        for epoch in 0..=clock.epoch + 1 {
-            assert_eq!(stake.voter_pubkey(epoch), &vote_pubkey);
-        }
-
+        clock.epoch += 1;
         // verify that delegate_stake can be called twice, 2nd is redelegate
         assert!(stake_keyed_account
             .delegate_stake(&vote_keyed_account, &clock, &Config::default(), &signers)
@@ -820,33 +819,34 @@ mod tests {
             voter_pubkey_epoch: 0,
             ..Stake::default()
         };
-        // verify that redelegation any number of times since first delegation works just fine,
-        //  and that the stake is delegated to the most recent vote account
-        for epoch in 0..=MAX_PRIOR_DELEGATES + 1 {
+        // verify that redelegation works when epoch is changing, that
+        //  wraparound works, and that the stake is delegated
+        //  to the most recent vote account
+        for epoch in 1..=MAX_PRIOR_DELEGATES + 2 {
             let voter_pubkey = Pubkey::new_rand();
-            let _ignored = stake.redelegate(&voter_pubkey, &VoteState::default(), 0);
-            assert_eq!(stake.voter_pubkey(epoch as u64), &voter_pubkey);
-        }
-
-        // get a new voter_pubkey
-        let voter_pubkey = Pubkey::new_rand();
-        // save off old voter_pubkey
-        let prior_voter_pubkey = stake.voter_pubkey;
-
-        // actually redelegate in epoch 1
-        let _ignored = stake.redelegate(&voter_pubkey, &VoteState::default(), 1);
-        // verify that delegation is delayed
-        assert_eq!(stake.voter_pubkey(0 as u64), &prior_voter_pubkey);
-        assert_eq!(stake.voter_pubkey(1 as u64), &prior_voter_pubkey);
-        assert_eq!(stake.voter_pubkey(2 as u64), &voter_pubkey);
-
-        // verify that prior_delegates wraps around safely...
-        for epoch in 0..=MAX_PRIOR_DELEGATES + 1 {
-            let voter_pubkey = Pubkey::new_rand();
-            let prior_voter_pubkey = stake.voter_pubkey;
-            let _ignored = stake.redelegate(&voter_pubkey, &VoteState::default(), epoch as u64);
-            assert_eq!(stake.voter_pubkey(epoch as u64), &prior_voter_pubkey);
-            assert_eq!(stake.voter_pubkey((epoch + 1) as u64), &voter_pubkey);
+            assert_eq!(
+                stake.redelegate(
+                    &voter_pubkey,
+                    &VoteState::default(),
+                    &sysvar::clock::Clock {
+                        epoch: epoch as u64,
+                        ..sysvar::clock::Clock::default()
+                    },
+                ),
+                Ok(())
+            );
+            assert_eq!(
+                stake.redelegate(
+                    &voter_pubkey,
+                    &VoteState::default(),
+                    &sysvar::clock::Clock {
+                        epoch: epoch as u64,
+                        ..sysvar::clock::Clock::default()
+                    },
+                ),
+                Err(StakeError::TooSoonToRedelegate)
+            );
+            assert_eq!(stake.voter_pubkey, voter_pubkey);
         }
     }
 
@@ -1908,7 +1908,7 @@ mod tests {
         )
         .expect("stake_account");
 
-        let clock = sysvar::clock::Clock::default();
+        let mut clock = sysvar::clock::Clock::default();
 
         let vote_pubkey = Pubkey::new_rand();
         let mut vote_account =
@@ -1943,6 +1943,8 @@ mod tests {
             KeyedAccount::new(&new_voter_pubkey, false, &mut new_vote_account);
         new_vote_keyed_account.set_state(&vote_state).unwrap();
 
+        // time passes, so we can re-delegate
+        clock.epoch += 1;
         // Random other account should fail
         assert_eq!(
             stake_keyed_account.delegate_stake(
@@ -1966,7 +1968,7 @@ mod tests {
             Ok(())
         );
         let stake = StakeState::stake_from(&stake_keyed_account.account).unwrap();
-        assert_eq!(stake.voter_pubkey(0), &new_voter_pubkey);
+        assert_eq!(stake.voter_pubkey, new_voter_pubkey);
 
         // Test another staking action
         assert_eq!(
diff --git a/runtime/src/stakes.rs b/runtime/src/stakes.rs
index bcae8d5bc1..f7b93c4729 100644
--- a/runtime/src/stakes.rs
+++ b/runtime/src/stakes.rs
@@ -85,7 +85,7 @@ impl Stakes {
             .iter()
             .map(|(_, stake_account)| {
                 StakeState::stake_from(stake_account).map_or(0, |stake| {
-                    if stake.voter_pubkey(epoch) == voter_pubkey {
+                    if &stake.voter_pubkey == voter_pubkey {
                         stake.stake(epoch, stake_history)
                     } else {
                         0
@@ -129,7 +129,7 @@ impl Stakes {
             let old_stake = self.stake_accounts.get(pubkey).and_then(|old_account| {
                 StakeState::stake_from(old_account).map(|stake| {
                     (
-                        *stake.voter_pubkey(self.epoch),
+                        stake.voter_pubkey,
                         stake.stake(self.epoch, Some(&self.stake_history)),
                     )
                 })
@@ -137,7 +137,7 @@ impl Stakes {
 
             let stake = StakeState::stake_from(account).map(|stake| {
                 (
-                    *stake.voter_pubkey(self.epoch),
+                    stake.voter_pubkey,
                     if account.lamports != 0 {
                         stake.stake(self.epoch, Some(&self.stake_history))
                     } else {