diff --git a/linera-chain/src/block.rs b/linera-chain/src/block.rs
index cd068e6aa48b..f2cf31067180 100644
--- a/linera-chain/src/block.rs
+++ b/linera-chain/src/block.rs
@@ -79,3 +79,23 @@ impl ConfirmedBlock {
         self.executed_block
     }
 }
+
+use linera_base::{data_types::BlockHeight, identifiers::ChainId};
+use linera_execution::committee::Epoch;
+
+#[derive(Debug, PartialEq, Eq, Hash, Clone, Deserialize, Serialize)]
+pub struct Timeout {
+    pub chain_id: ChainId,
+    pub height: BlockHeight,
+    pub epoch: Epoch,
+}
+
+impl Timeout {
+    pub fn new(chain_id: ChainId, height: BlockHeight, epoch: Epoch) -> Self {
+        Self {
+            chain_id,
+            height,
+            epoch,
+        }
+    }
+}
diff --git a/linera-chain/src/certificate.rs b/linera-chain/src/certificate.rs
index 69b031b16195..e477b46b2283 100644
--- a/linera-chain/src/certificate.rs
+++ b/linera-chain/src/certificate.rs
@@ -13,10 +13,13 @@ use linera_base::{
     identifiers::BlobId,
 };
 use linera_execution::committee::{Committee, ValidatorName};
-use serde::{ser::Serializer, Deserialize, Deserializer, Serialize};
+use serde::{
+    ser::{Serialize, SerializeStruct, Serializer},
+    Deserialize, Deserializer,
+};
 
 use crate::{
-    block::{ConfirmedBlock, ValidatedBlock},
+    block::{ConfirmedBlock, Timeout, ValidatedBlock},
     data_types::{
         Certificate, CertificateValue, ExecutedBlock, HashedCertificateValue, LiteCertificate,
         LiteValue,
@@ -30,6 +33,9 @@ pub type ValidatedBlockCertificate = GenericCertificate<ValidatedBlock>;
 /// Certificate for a [`ConfirmedBlock`] instance.
 pub type ConfirmedBlockCertificate = GenericCertificate<ConfirmedBlock>;
 
+/// Certificate for a Timeout instance.
+pub type TimeoutCertificate = GenericCertificate<Timeout>;
+
 /// Generic type representing a certificate for `value` of type `T`.
 pub struct GenericCertificate<T> {
     value: Hashed<T>,
@@ -69,13 +75,25 @@ impl<T: Debug> Debug for GenericCertificate<T> {
     }
 }
 
-// NOTE: For backwards compatiblity reasons we serialize the new `Certificate` type as the old
-// one. Otherwise we would be breaking the RPC API schemas. We can't implement generic serialization
-// for `Certificate<T>` since only specific `T`s have corresponding `CertificateValue` variants.
 impl Serialize for ValidatedBlockCertificate {
     fn serialize<S: Serializer>(&self, serializer: S) -> Result<S::Ok, S::Error> {
-        let cert = Certificate::from(self.clone());
-        cert.serialize(serializer)
+        let mut state = serializer.serialize_struct("ValidatedBlockCertificate", 4)?;
+        state.serialize_field("hash", &self.value.hash())?;
+        state.serialize_field("value", &self.inner())?;
+        state.serialize_field("round", &self.round)?;
+        state.serialize_field("signatures", &self.signatures)?;
+        state.end()
+    }
+}
+
+impl Serialize for TimeoutCertificate {
+    fn serialize<S: Serializer>(&self, serializer: S) -> Result<S::Ok, S::Error> {
+        let mut state = serializer.serialize_struct("TimeoutCertificate", 4)?;
+        state.serialize_field("hash", &self.value.hash())?;
+        state.serialize_field("value", &self.inner())?;
+        state.serialize_field("round", &self.round)?;
+        state.serialize_field("signatures", &self.signatures)?;
+        state.end()
     }
 }
 
@@ -84,7 +102,42 @@ impl<'de> Deserialize<'de> for ValidatedBlockCertificate {
     where
         D: Deserializer<'de>,
     {
-        Certificate::deserialize(deserializer).map(ValidatedBlockCertificate::from)
+        #[derive(Deserialize)]
+        #[serde(rename = "ValidatedBlockCertificate")]
+        struct Inner {
+            hash: CryptoHash,
+            value: ValidatedBlock,
+            round: Round,
+            signatures: Vec<(ValidatorName, Signature)>,
+        }
+        let value = Inner::deserialize(deserializer)?;
+        Ok(Self {
+            value: Hashed::unchecked_new(value.value, value.hash),
+            round: value.round,
+            signatures: value.signatures,
+        })
+    }
+}
+
+impl<'de> Deserialize<'de> for TimeoutCertificate {
+    fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
+    where
+        D: Deserializer<'de>,
+    {
+        #[derive(Deserialize)]
+        #[serde(rename = "TimeoutCertificate")]
+        struct Inner {
+            hash: CryptoHash,
+            value: Timeout,
+            round: Round,
+            signatures: Vec<(ValidatorName, Signature)>,
+        }
+        let value = Inner::deserialize(deserializer)?;
+        Ok(Self {
+            value: Hashed::unchecked_new(value.value, value.hash),
+            round: value.round,
+            signatures: value.signatures,
+        })
     }
 }
 
@@ -129,7 +182,23 @@ impl From<ValidatedBlockCertificate> for Certificate {
     }
 }
 
-// TODO(#2842): In practice, it should be HashedCertificateValue = Hashed<CertificateValue>
+impl From<TimeoutCertificate> for Certificate {
+    fn from(cert: TimeoutCertificate) -> Certificate {
+        let TimeoutCertificate {
+            value,
+            round,
+            signatures,
+        } = cert;
+        let timeout = value.into_inner();
+        Certificate::new(
+            HashedCertificateValue::new_timeout(timeout.chain_id, timeout.height, timeout.epoch),
+            round,
+            signatures,
+        )
+    }
+}
+
+// In practice, it should be HashedCertificateValue = Hashed<CertificateValue>
 // but [`HashedCertificateValue`] is used in too many places to change it now.
 /// Wrapper type around hashed instance of `T` type.
 pub struct Hashed<T> {
@@ -319,3 +388,22 @@ impl TryFrom<Certificate> for ConfirmedBlockCertificate {
         }
     }
 }
+
+impl From<Certificate> for TimeoutCertificate {
+    fn from(cert: Certificate) -> Self {
+        let signatures = cert.signatures().clone();
+        let hash = cert.value.hash();
+        match cert.value.into_inner() {
+            CertificateValue::Timeout {
+                chain_id,
+                epoch,
+                height,
+            } => Self {
+                value: Hashed::unchecked_new(Timeout::new(chain_id, height, epoch), hash),
+                round: cert.round,
+                signatures,
+            },
+            _ => panic!("Expected a timeout certificate"),
+        }
+    }
+}
diff --git a/linera-chain/src/manager.rs b/linera-chain/src/manager.rs
index 43f0b195a4c7..4017b4919416 100644
--- a/linera-chain/src/manager.rs
+++ b/linera-chain/src/manager.rs
@@ -81,14 +81,13 @@ use linera_execution::committee::Epoch;
 use rand_chacha::{rand_core::SeedableRng, ChaCha8Rng};
 use rand_distr::{Distribution, WeightedAliasIndex};
 use serde::{Deserialize, Serialize};
-use tracing::error;
 
 use crate::{
     data_types::{
-        Block, BlockExecutionOutcome, BlockProposal, Certificate, CertificateValue,
-        HashedCertificateValue, LiteVote, ProposalContent, Vote,
+        Block, BlockExecutionOutcome, BlockProposal, CertificateValue, HashedCertificateValue,
+        LiteVote, ProposalContent, Vote,
     },
-    types::{ConfirmedBlockCertificate, ValidatedBlockCertificate},
+    types::{ConfirmedBlockCertificate, TimeoutCertificate, ValidatedBlockCertificate},
     ChainError,
 };
 
@@ -117,7 +116,7 @@ pub struct ChainManager {
     /// validator).
     pub locked: Option<ValidatedBlockCertificate>,
     /// Latest leader timeout certificate we have received.
-    pub timeout: Option<Certificate>,
+    pub timeout: Option<TimeoutCertificate>,
     /// Latest vote we have cast, to validate or confirm.
     pub pending: Option<Vote>,
     /// Latest timeout vote we cast.
@@ -470,12 +469,11 @@ impl ChainManager {
 
     /// Updates the round number and timer if the timeout certificate is from a higher round than
     /// any known certificate.
-    pub fn handle_timeout_certificate(&mut self, certificate: Certificate, local_time: Timestamp) {
-        if !certificate.value().is_timeout() {
-            // Unreachable: This is only called with timeout certificates.
-            error!("Unexpected certificate; expected leader timeout");
-            return;
-        }
+    pub fn handle_timeout_certificate(
+        &mut self,
+        certificate: TimeoutCertificate,
+        local_time: Timestamp,
+    ) {
         let round = certificate.round;
         if let Some(known_certificate) = &self.timeout {
             if known_certificate.round >= round {
@@ -565,7 +563,7 @@ pub struct ChainManagerInfo {
     /// validator).
     pub requested_locked: Option<Box<ValidatedBlockCertificate>>,
     /// Latest timeout certificate we have seen.
-    pub timeout: Option<Box<Certificate>>,
+    pub timeout: Option<Box<TimeoutCertificate>>,
     /// Latest vote we cast (either to validate or to confirm a block).
     pub pending: Option<LiteVote>,
     /// Latest timeout vote we cast.
diff --git a/linera-core/src/chain_worker/actor.rs b/linera-core/src/chain_worker/actor.rs
index 896a6ffc83ff..6c343a5cda66 100644
--- a/linera-core/src/chain_worker/actor.rs
+++ b/linera-core/src/chain_worker/actor.rs
@@ -16,10 +16,9 @@ use linera_base::{
 };
 use linera_chain::{
     data_types::{
-        Block, BlockProposal, Certificate, ExecutedBlock, HashedCertificateValue, MessageBundle,
-        Origin, Target,
+        Block, BlockProposal, ExecutedBlock, HashedCertificateValue, MessageBundle, Origin, Target,
     },
-    types::{ConfirmedBlockCertificate, ValidatedBlockCertificate},
+    types::{ConfirmedBlockCertificate, TimeoutCertificate, ValidatedBlockCertificate},
     ChainStateView,
 };
 use linera_execution::{
@@ -45,7 +44,8 @@ where
     #[cfg(with_testing)]
     ReadCertificate {
         height: BlockHeight,
-        callback: oneshot::Sender<Result<Option<Certificate>, WorkerError>>,
+        callback:
+            oneshot::Sender<Result<Option<linera_chain::data_types::Certificate>, WorkerError>>,
     },
 
     /// Search for a bundle in one of the chain's inboxes.
@@ -84,7 +84,7 @@ where
 
     /// Process a leader timeout issued for this multi-owner chain.
     ProcessTimeout {
-        certificate: Certificate,
+        certificate: TimeoutCertificate,
         callback: oneshot::Sender<Result<(ChainInfoResponse, NetworkActions), WorkerError>>,
     },
 
diff --git a/linera-core/src/chain_worker/state/attempted_changes.rs b/linera-core/src/chain_worker/state/attempted_changes.rs
index 7485641df382..0604113416a8 100644
--- a/linera-core/src/chain_worker/state/attempted_changes.rs
+++ b/linera-core/src/chain_worker/state/attempted_changes.rs
@@ -12,11 +12,10 @@ use linera_base::{
 };
 use linera_chain::{
     data_types::{
-        BlockExecutionOutcome, BlockProposal, Certificate, CertificateValue, MessageBundle, Origin,
-        Target,
+        BlockExecutionOutcome, BlockProposal, Certificate, MessageBundle, Origin, Target,
     },
     manager,
-    types::{ConfirmedBlockCertificate, ValidatedBlockCertificate},
+    types::{ConfirmedBlockCertificate, TimeoutCertificate, ValidatedBlockCertificate},
     ChainStateView,
 };
 use linera_execution::{
@@ -68,17 +67,8 @@ where
     /// Processes a leader timeout issued for this multi-owner chain.
     pub(super) async fn process_timeout(
         &mut self,
-        certificate: Certificate,
+        certificate: TimeoutCertificate,
     ) -> Result<(ChainInfoResponse, NetworkActions), WorkerError> {
-        let (chain_id, height, epoch) = match certificate.value() {
-            CertificateValue::Timeout {
-                chain_id,
-                height,
-                epoch,
-                ..
-            } => (*chain_id, *height, *epoch),
-            _ => panic!("Expecting a leader timeout certificate"),
-        };
         // Check that the chain is active and ready for this timeout.
         // Verify the certificate. Returns a catch-all error to make client code more robust.
         self.state.ensure_is_active()?;
@@ -90,11 +80,11 @@ where
             .current_committee()
             .expect("chain is active");
         ensure!(
-            epoch == chain_epoch,
+            certificate.inner().epoch == chain_epoch,
             WorkerError::InvalidEpoch {
-                chain_id,
+                chain_id: certificate.inner().chain_id,
                 chain_epoch,
-                epoch
+                epoch: certificate.inner().epoch
             }
         );
         certificate.check(committee)?;
@@ -104,7 +94,7 @@ where
             .chain
             .tip_state
             .get()
-            .already_validated_block(height)?
+            .already_validated_block(certificate.inner().height)?
         {
             return Ok((
                 ChainInfoResponse::new(&self.state.chain, self.state.config.key_pair()),
@@ -112,19 +102,21 @@ where
             ));
         }
         let old_round = self.state.chain.manager.get().current_round;
+        let timeout_chainid = certificate.inner().chain_id;
+        let timeout_height = certificate.inner().height;
         self.state
             .chain
             .manager
             .get_mut()
-            .handle_timeout_certificate(
-                certificate.clone(),
-                self.state.storage.clock().current_time(),
-            );
+            .handle_timeout_certificate(certificate, self.state.storage.clock().current_time());
         let round = self.state.chain.manager.get().current_round;
         if round > old_round {
             actions.notifications.push(Notification {
-                chain_id,
-                reason: Reason::NewRound { height, round },
+                chain_id: timeout_chainid,
+                reason: Reason::NewRound {
+                    height: timeout_height,
+                    round,
+                },
             })
         }
         let info = ChainInfoResponse::new(&self.state.chain, self.state.config.key_pair());
diff --git a/linera-core/src/chain_worker/state/mod.rs b/linera-core/src/chain_worker/state/mod.rs
index 5b8f1d109983..80654435be1e 100644
--- a/linera-core/src/chain_worker/state/mod.rs
+++ b/linera-core/src/chain_worker/state/mod.rs
@@ -19,10 +19,10 @@ use linera_base::{
 };
 use linera_chain::{
     data_types::{
-        Block, BlockProposal, Certificate, ExecutedBlock, HashedCertificateValue, Medium,
-        MessageBundle, Origin, Target,
+        Block, BlockProposal, ExecutedBlock, HashedCertificateValue, Medium, MessageBundle, Origin,
+        Target,
     },
-    types::{ConfirmedBlockCertificate, ValidatedBlockCertificate},
+    types::{ConfirmedBlockCertificate, TimeoutCertificate, ValidatedBlockCertificate},
     ChainError, ChainStateView,
 };
 use linera_execution::{
@@ -130,7 +130,7 @@ where
     pub(super) async fn read_certificate(
         &mut self,
         height: BlockHeight,
-    ) -> Result<Option<Certificate>, WorkerError> {
+    ) -> Result<Option<linera_chain::data_types::Certificate>, WorkerError> {
         ChainWorkerStateWithTemporaryChanges::new(self)
             .await
             .read_certificate(height)
@@ -188,7 +188,7 @@ where
     /// Processes a leader timeout issued for this multi-owner chain.
     pub(super) async fn process_timeout(
         &mut self,
-        certificate: Certificate,
+        certificate: TimeoutCertificate,
     ) -> Result<(ChainInfoResponse, NetworkActions), WorkerError> {
         ChainWorkerStateWithAttemptedChanges::new(self)
             .await
diff --git a/linera-core/src/updater.rs b/linera-core/src/updater.rs
index 668bf864e1ea..e59d2c678b57 100644
--- a/linera-core/src/updater.rs
+++ b/linera-core/src/updater.rs
@@ -352,8 +352,8 @@ where
             }
         }
         if let Some(cert) = manager.timeout {
-            if cert.value().is_timeout() && cert.value().chain_id() == chain_id {
-                self.send_certificate(cert, CrossChainMessageDelivery::NonBlocking)
+            if cert.inner().chain_id == chain_id {
+                self.send_certificate(cert.into(), CrossChainMessageDelivery::NonBlocking)
                     .await?;
             }
         }
diff --git a/linera-core/src/worker.rs b/linera-core/src/worker.rs
index 23f3cb80e0ae..41c74abc0a22 100644
--- a/linera-core/src/worker.rs
+++ b/linera-core/src/worker.rs
@@ -25,7 +25,7 @@ use linera_chain::{
         Block, BlockExecutionOutcome, BlockProposal, Certificate, CertificateValue, ExecutedBlock,
         HashedCertificateValue, LiteCertificate, MessageBundle, Origin, Target,
     },
-    types::{ConfirmedBlockCertificate, ValidatedBlockCertificate},
+    types::{ConfirmedBlockCertificate, TimeoutCertificate, ValidatedBlockCertificate},
     ChainStateView,
 };
 use linera_execution::{committee::Epoch, Query, Response};
@@ -514,12 +514,10 @@ where
     #[instrument(level = "trace", skip(self, certificate))]
     async fn process_timeout(
         &self,
-        certificate: Certificate,
+        certificate: TimeoutCertificate,
     ) -> Result<(ChainInfoResponse, NetworkActions), WorkerError> {
-        let CertificateValue::Timeout { chain_id, .. } = certificate.value() else {
-            panic!("Expecting a leader timeout certificate");
-        };
-        self.query_chain_worker(*chain_id, move |callback| {
+        let chain_id = certificate.inner().chain_id;
+        self.query_chain_worker(chain_id, move |callback| {
             ChainWorkerRequest::ProcessTimeout {
                 certificate,
                 callback,
@@ -792,7 +790,10 @@ where
             }
             CertificateValue::Timeout { .. } => {
                 // Handle the leader timeout.
-                self.process_timeout(certificate).await?
+                // Note: This conversion panics if `certificate` is not a timeout certificate
+                // but we just checked that it is.
+                let timeout_certificate = certificate.into();
+                self.process_timeout(timeout_certificate).await?
             }
         };
 
diff --git a/linera-rpc/tests/snapshots/format__format.yaml.snap b/linera-rpc/tests/snapshots/format__format.yaml.snap
index 032ee89e0e7b..f0d51941c49c 100644
--- a/linera-rpc/tests/snapshots/format__format.yaml.snap
+++ b/linera-rpc/tests/snapshots/format__format.yaml.snap
@@ -266,10 +266,10 @@ ChainManagerInfo:
           TYPENAME: BlockProposal
     - requested_locked:
         OPTION:
-          TYPENAME: Certificate
+          TYPENAME: ValidatedBlockCertificate
     - timeout:
         OPTION:
-          TYPENAME: Certificate
+          TYPENAME: TimeoutCertificate
     - pending:
         OPTION:
           TYPENAME: LiteVote
@@ -1029,6 +1029,27 @@ SystemOperation:
           TYPENAME: AdminOperation
 TimeDelta:
   NEWTYPESTRUCT: U64
+Timeout:
+  STRUCT:
+    - chain_id:
+        TYPENAME: ChainId
+    - height:
+        TYPENAME: BlockHeight
+    - epoch:
+        TYPENAME: Epoch
+TimeoutCertificate:
+  STRUCT:
+    - hash:
+        TYPENAME: CryptoHash
+    - value:
+        TYPENAME: Timeout
+    - round:
+        TYPENAME: Round
+    - signatures:
+        SEQ:
+          TUPLE:
+            - TYPENAME: ValidatorName
+            - TYPENAME: Signature
 TimeoutConfig:
   STRUCT:
     - fast_round_duration:
@@ -1052,6 +1073,23 @@ UserApplicationDescription:
     - required_application_ids:
         SEQ:
           TYPENAME: ApplicationId
+ValidatedBlock:
+  STRUCT:
+    - executed_block:
+        TYPENAME: ExecutedBlock
+ValidatedBlockCertificate:
+  STRUCT:
+    - hash:
+        TYPENAME: CryptoHash
+    - value:
+        TYPENAME: ValidatedBlock
+    - round:
+        TYPENAME: Round
+    - signatures:
+        SEQ:
+          TUPLE:
+            - TYPENAME: ValidatorName
+            - TYPENAME: Signature
 ValidatorName:
   NEWTYPESTRUCT:
     TYPENAME: PublicKey