diff --git a/crates/catalog/rest/src/catalog.rs b/crates/catalog/rest/src/catalog.rs
index b6ca41df7..4e380727b 100644
--- a/crates/catalog/rest/src/catalog.rs
+++ b/crates/catalog/rest/src/catalog.rs
@@ -521,7 +521,7 @@ mod _serde {
 
     use serde_derive::{Deserialize, Serialize};
 
-    use iceberg::spec::{PartitionSpec, Schema, SortOrder, TableMetadata, UnboundPartitionSpec};
+    use iceberg::spec::{Schema, SortOrder, TableMetadata, UnboundPartitionSpec};
     use iceberg::{Error, ErrorKind, Namespace, TableIdent, TableRequirement, TableUpdate};
 
     pub(super) const OK: u16 = 200u16;
@@ -686,9 +686,9 @@ mod tests {
     use chrono::{TimeZone, Utc};
     use iceberg::spec::ManifestListLocation::ManifestListFile;
     use iceberg::spec::{
-        FormatVersion, NestedField, NullOrder, Operation, PartitionField, PartitionSpec,
-        PrimitiveType, Schema, Snapshot, SnapshotLog, SortDirection, SortField, SortOrder, Summary,
-        Transform, Type,
+        FormatVersion, NestedField, NullOrder, Operation, PrimitiveType, Schema, Snapshot,
+        SnapshotLog, SortDirection, SortField, SortOrder, Summary, Transform, Type,
+        UnboundPartitionField, UnboundPartitionSpec,
     };
     use iceberg::transaction::Transaction;
     use mockito::{Mock, Server, ServerGuard};
@@ -1233,14 +1233,12 @@ mod tests {
             )
             .properties(HashMap::from([("owner".to_string(), "testx".to_string())]))
             .partition_spec(
-                PartitionSpec::builder()
-                    .with_fields(vec![PartitionField::builder()
+                UnboundPartitionSpec::builder()
+                    .with_fields(vec![UnboundPartitionField::builder()
                         .source_id(1)
-                        .field_id(1000)
                         .transform(Transform::Truncate(3))
                         .name("id".to_string())
                         .build()])
-                    .with_spec_id(1)
                     .build()
                     .unwrap(),
             )
diff --git a/crates/iceberg/src/catalog/mod.rs b/crates/iceberg/src/catalog/mod.rs
index 142ea3029..a0b69a154 100644
--- a/crates/iceberg/src/catalog/mod.rs
+++ b/crates/iceberg/src/catalog/mod.rs
@@ -20,7 +20,9 @@
 use serde_derive::{Deserialize, Serialize};
 use urlencoding::encode;
 
-use crate::spec::{FormatVersion, PartitionSpec, Schema, Snapshot, SnapshotReference, SortOrder, UnboundPartitionSpec};
+use crate::spec::{
+    FormatVersion, Schema, Snapshot, SnapshotReference, SortOrder, UnboundPartitionSpec,
+};
 use crate::table::Table;
 use crate::{Error, ErrorKind, Result};
 use async_trait::async_trait;
@@ -429,9 +431,9 @@ pub enum TableUpdate {
 mod tests {
     use crate::spec::ManifestListLocation::ManifestListFile;
     use crate::spec::{
-        FormatVersion, NestedField, NullOrder, Operation, PartitionField, PartitionSpec,
-        PrimitiveType, Schema, Snapshot, SnapshotReference, SnapshotRetention, SortDirection,
-        SortField, SortOrder, Summary, Transform, Type,
+        FormatVersion, NestedField, NullOrder, Operation, PrimitiveType, Schema, Snapshot,
+        SnapshotReference, SnapshotRetention, SortDirection, SortField, SortOrder, Summary,
+        Transform, Type, UnboundPartitionField, UnboundPartitionSpec,
     };
     use crate::{NamespaceIdent, TableIdent, TableRequirement, TableUpdate};
     use serde::de::DeserializeOwned;
@@ -758,23 +760,19 @@ mod tests {
 {
     "action": "add-spec",
     "spec": {
-        "spec-id": 1,
         "fields": [
             {
                 "source-id": 4,
-                "field-id": 1000,
                 "name": "ts_day",
                 "transform": "day"
             },
             {
                 "source-id": 1,
-                "field-id": 1001,
                 "name": "id_bucket",
                 "transform": "bucket[16]"
             },
             {
                 "source-id": 2,
-                "field-id": 1002,
                 "name": "id_truncate",
                 "transform": "truncate[4]"
             }
@@ -783,28 +781,24 @@ mod tests {
 }
         "#,
             TableUpdate::AddSpec {
-                spec: PartitionSpec::builder()
-                    .with_spec_id(1)
-                    .with_partition_field(
-                        PartitionField::builder()
+                spec: UnboundPartitionSpec::builder()
+                    .with_unbound_partition_field(
+                        UnboundPartitionField::builder()
                             .source_id(4)
-                            .field_id(1000)
                             .name("ts_day".to_string())
                             .transform(Transform::Day)
                             .build(),
                     )
-                    .with_partition_field(
-                        PartitionField::builder()
+                    .with_unbound_partition_field(
+                        UnboundPartitionField::builder()
                             .source_id(1)
-                            .field_id(1001)
                             .name("id_bucket".to_string())
                             .transform(Transform::Bucket(16))
                             .build(),
                     )
-                    .with_partition_field(
-                        PartitionField::builder()
+                    .with_unbound_partition_field(
+                        UnboundPartitionField::builder()
                             .source_id(2)
-                            .field_id(1002)
                             .name("id_truncate".to_string())
                             .transform(Transform::Truncate(4))
                             .build(),
diff --git a/crates/iceberg/src/spec/partition.rs b/crates/iceberg/src/spec/partition.rs
index e2f67740b..774162dec 100644
--- a/crates/iceberg/src/spec/partition.rs
+++ b/crates/iceberg/src/spec/partition.rs
@@ -18,13 +18,11 @@
 /*!
  * Partitioning
 */
-use crate::error::{Error, ErrorKind, Result};
 use serde::{Deserialize, Serialize};
 use std::sync::Arc;
 use typed_builder::TypedBuilder;
 
-use super::DEFAULT_SPEC_ID;
-use super::{schema::SchemaRef, transform::Transform};
+use super::transform::Transform;
 
 /// Reference to [`PartitionSpec`].
 pub type PartitionSpecRef = Arc<PartitionSpec>;
@@ -62,11 +60,9 @@ impl PartitionSpec {
     }
 }
 
-static PARTITION_DATA_ID_START: i32 = 1000;
-
 /// Reference to [`UnboundPartitionSpec`].
 pub type UnboundPartitionSpecRef = Arc<UnboundPartitionSpec>;
-#[derive(Debug, Serialize, Deserialize, PartialEq, Eq, Clone)]
+#[derive(Debug, Serialize, Deserialize, PartialEq, Eq, Clone, TypedBuilder)]
 #[serde(rename_all = "kebab-case")]
 /// Unbound partition field can be built without a schema and later bound to a schema.
 pub struct UnboundPartitionField {
@@ -74,6 +70,7 @@ pub struct UnboundPartitionField {
     pub source_id: i32,
     /// A partition field id that is used to identify a partition field and is unique within a partition spec.
     /// In v2 table metadata, it is unique across all partition specs.
+    #[builder(default, setter(strip_option))]
     pub partition_id: Option<i32>,
     /// A partition name.
     pub name: String,
@@ -87,6 +84,7 @@ pub struct UnboundPartitionField {
 /// Unbound partition spec can be built without a schema and later bound to a schema.
 pub struct UnboundPartitionSpec {
     /// Identifier for PartitionSpec
+    #[builder(default, setter(strip_option))]
     pub spec_id: Option<i32>,
     /// Details of the partition spec
     #[builder(setter(each(name = "with_unbound_partition_field")))]
@@ -94,16 +92,10 @@ pub struct UnboundPartitionSpec {
 }
 
 impl UnboundPartitionSpec {
-    /// last assigned id for partitioned field
-    pub fn unpartitioned_last_assigned_id() -> i32 {
-        PARTITION_DATA_ID_START - 1
-    }
-
     /// Create unbound partition spec builer
     pub fn builder() -> UnboundPartitionSpecBuilder {
         UnboundPartitionSpecBuilder::default()
     }
-
 }
 
 #[cfg(test)]