diff --git a/src/models/activity.rs b/src/models/activity.rs
new file mode 100644
index 0000000..9170976
--- /dev/null
+++ b/src/models/activity.rs
@@ -0,0 +1,122 @@
+use serde::{Deserialize, Serialize};
+use serde_json::{Map, Value};
+
+/// One row of the activity log, as `GET /activities` returns it.
+///
+/// Every reference is a hashed id, or an empty string when the activity does
+/// not concern that kind of record. `activity_type_id` arrives as a string
+/// here but as a number in the [feed](ActivityFeedEntry).
+#[derive(Debug, Clone, Default, Serialize, Deserialize)]
+pub struct Activity {
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub id: Option<String>,
+    #[serde(default, deserialize_with = "super::common::null_to_default")]
+    pub activity_type_id: String,
+    #[serde(default, deserialize_with = "super::common::null_to_default")]
+    pub user_id: String,
+    #[serde(default, deserialize_with = "super::common::null_to_default")]
+    pub company_id: String,
+    #[serde(default, deserialize_with = "super::common::null_to_default")]
+    pub client_id: String,
+    #[serde(default, deserialize_with = "super::common::null_to_default")]
+    pub contact_id: String,
+    #[serde(default, deserialize_with = "super::common::null_to_default")]
+    pub vendor_id: String,
+    #[serde(default, deserialize_with = "super::common::null_to_default")]
+    pub vendor_contact_id: String,
+    #[serde(default, deserialize_with = "super::common::null_to_default")]
+    pub invoice_id: String,
+    #[serde(default, deserialize_with = "super::common::null_to_default")]
+    pub quote_id: String,
+    #[serde(default, deserialize_with = "super::common::null_to_default")]
+    pub credit_id: String,
+    #[serde(default, deserialize_with = "super::common::null_to_default")]
+    pub payment_id: String,
+    #[serde(default, deserialize_with = "super::common::null_to_default")]
+    pub recurring_invoice_id: String,
+    #[serde(default, deserialize_with = "super::common::null_to_default")]
+    pub recurring_expense_id: String,
+    #[serde(default, deserialize_with = "super::common::null_to_default")]
+    pub purchase_order_id: String,
+    #[serde(default, deserialize_with = "super::common::null_to_default")]
+    pub expense_id: String,
+    #[serde(default, deserialize_with = "super::common::null_to_default")]
+    pub task_id: String,
+    #[serde(default, deserialize_with = "super::common::null_to_default")]
+    pub token_id: String,
+    #[serde(default, deserialize_with = "super::common::null_to_default")]
+    pub is_system: bool,
+    #[serde(default, deserialize_with = "super::common::null_to_default")]
+    pub notes: String,
+    #[serde(default, deserialize_with = "super::common::null_to_default")]
+    pub ip: String,
+    #[serde(default)]
+    pub created_at: Option<i64>,
+    #[serde(default)]
+    pub updated_at: Option<i64>,
+
+    #[serde(flatten)]
+    pub extra: Map<String, Value>,
+}
+
+/// A named record an activity refers to: the display label and its hashed id.
+#[derive(Debug, Clone, Default, Serialize, Deserialize)]
+pub struct ActivityRef {
+    #[serde(default, deserialize_with = "super::common::null_to_default")]
+    pub label: String,
+    #[serde(default, deserialize_with = "super::common::null_to_default")]
+    pub hashed_id: String,
+
+    #[serde(flatten)]
+    pub extra: Map<String, Value>,
+}
+
+/// One entry of the activity feed (`activity_feed`, `entity_activity`).
+///
+/// A different shape from [`Activity`]: the server resolves the records an
+/// activity mentions into labelled references. Which references are present
+/// depends on the activity type, so each is optional, and any the server adds
+/// that this does not name lands in `extra`.
+#[derive(Debug, Clone, Default, Serialize, Deserialize)]
+pub struct ActivityFeedEntry {
+    #[serde(default, deserialize_with = "super::common::null_to_default")]
+    pub id: String,
+    #[serde(default, deserialize_with = "super::common::null_to_default")]
+    pub hashed_id: String,
+    #[serde(default, deserialize_with = "super::common::int_or_numeric_string")]
+    pub activity_type_id: i64,
+    #[serde(default, deserialize_with = "super::common::null_to_default")]
+    pub notes: String,
+    #[serde(default, deserialize_with = "super::common::null_to_default")]
+    pub ip: String,
+    #[serde(default, deserialize_with = "super::common::int_or_numeric_string")]
+    pub created_at: i64,
+
+    #[serde(default, skip_serializing_if = "Option::is_none")]
+    pub user: Option<ActivityRef>,
+    #[serde(default, skip_serializing_if = "Option::is_none")]
+    pub client: Option<ActivityRef>,
+    #[serde(default, skip_serializing_if = "Option::is_none")]
+    pub vendor: Option<ActivityRef>,
+    #[serde(default, skip_serializing_if = "Option::is_none")]
+    pub invoice: Option<ActivityRef>,
+    #[serde(default, skip_serializing_if = "Option::is_none")]
+    pub quote: Option<ActivityRef>,
+    #[serde(default, skip_serializing_if = "Option::is_none")]
+    pub credit: Option<ActivityRef>,
+    #[serde(default, skip_serializing_if = "Option::is_none")]
+    pub payment: Option<ActivityRef>,
+    #[serde(default, skip_serializing_if = "Option::is_none")]
+    pub task: Option<ActivityRef>,
+    #[serde(default, skip_serializing_if = "Option::is_none")]
+    pub expense: Option<ActivityRef>,
+    #[serde(default, skip_serializing_if = "Option::is_none")]
+    pub purchase_order: Option<ActivityRef>,
+    #[serde(default, skip_serializing_if = "Option::is_none")]
+    pub recurring_invoice: Option<ActivityRef>,
+    #[serde(default, skip_serializing_if = "Option::is_none")]
+    pub recurring_expense: Option<ActivityRef>,
+
+    #[serde(flatten)]
+    pub extra: Map<String, Value>,
+}
diff --git a/src/models/common.rs b/src/models/common.rs
index 3cfc0d8..4545e12 100644
--- a/src/models/common.rs
+++ b/src/models/common.rs
@@ -154,6 +154,32 @@ where
     }
 }
 
+/// Deserializes an integer that may arrive as a JSON number or as a numeric
+/// string.
+///
+/// The OpenAPI spec calls `frequency_id` a number on recurring invoices and
+/// expenses, but a real 5.13.50 server returns the string `"5"`. A strict
+/// `i64` made that a hard decode error *after* the record had already been
+/// created. A string that is not a whole number is still an error.
+pub(crate) fn int_or_numeric_string<'de, D>(deserializer: D) -> Result<i64, D::Error>
+where
+    D: Deserializer<'de>,
+{
+    match Option::<Value>::deserialize(deserializer)? {
+        None | Some(Value::Null) => Ok(0),
+        Some(Value::Number(n)) => n
+            .as_i64()
+            .ok_or_else(|| serde::de::Error::custom(format!("expected a whole number, got {n}"))),
+        Some(Value::String(s)) if s.is_empty() => Ok(0),
+        Some(Value::String(s)) => s.trim().parse().map_err(|_| {
+            serde::de::Error::custom(format!("expected a whole number, got string `{s}`"))
+        }),
+        Some(other) => Err(serde::de::Error::custom(format!(
+            "expected a whole number or numeric string, got {other}"
+        ))),
+    }
+}
+
 /// Body for a bulk action (`POST /{resource}/bulk`).
 ///
 /// The action set varies by resource; `archive`, `restore`, and `delete` work
@@ -174,3 +200,15 @@ impl BulkRequest {
         }
     }
 }
+
+/// The `{"message": "..."}` body that action endpoints answer with.
+///
+/// `message` is defaulted so a reply that carries none still decodes.
+/// Anything else the server adds is kept in `extra`.
+#[derive(Debug, Clone, Default, Deserialize)]
+pub struct MessageResponse {
+    #[serde(default, deserialize_with = "null_to_default")]
+    pub message: String,
+    #[serde(flatten)]
+    pub extra: serde_json::Map<String, Value>,
+}
diff --git a/src/models/mod.rs b/src/models/mod.rs
index d1961db..488ca46 100644
--- a/src/models/mod.rs
+++ b/src/models/mod.rs
@@ -1,3 +1,4 @@
+mod activity;
 mod bank_integration;
 mod bank_transaction;
 mod bank_transaction_rule;
@@ -35,12 +36,15 @@ mod user;
 mod vendor;
 mod webhook;
 
+pub use activity::{Activity, ActivityFeedEntry, ActivityRef};
 pub use bank_integration::BankIntegration;
 pub use bank_transaction::BankTransaction;
 pub use bank_transaction_rule::BankTransactionRule;
 pub use client::{Client, ClientContact};
 pub use client_gateway_token::ClientGatewayToken;
-pub use common::{BulkRequest, ItemResponse, ListParams, ListResponse, Meta, Pagination};
+pub use common::{
+    BulkRequest, ItemResponse, ListParams, ListResponse, MessageResponse, Meta, Pagination,
+};
 pub use company::Company;
 pub use company_gateway::CompanyGateway;
 pub use company_token::CompanyToken;
@@ -61,7 +65,7 @@ pub use recurring_expense::RecurringExpense;
 pub use recurring_invoice::{RecurringInvoice, RecurringQuote};
 pub use search::{SearchHit, SearchResults};
 pub use statics::{Currency, DateFormat, StaticItem, Statics};
-pub use subscription::Subscription;
+pub use subscription::{Subscription, SubscriptionStep};
 pub use system_log::SystemLog;
 pub use tag::Tag;
 pub use task::Task;
diff --git a/src/models/subscription.rs b/src/models/subscription.rs
index 4837bf0..76301d0 100644
--- a/src/models/subscription.rs
+++ b/src/models/subscription.rs
@@ -55,3 +55,16 @@ pub struct Subscription {
     #[serde(flatten)]
     pub extra: Map<String, Value>,
 }
+
+/// One step of the subscription purchase flow and the steps it depends on,
+/// as returned by `GET /subscriptions/steps`.
+#[derive(Debug, Clone, Default, Serialize, Deserialize)]
+pub struct SubscriptionStep {
+    #[serde(default, deserialize_with = "super::common::null_to_default")]
+    pub id: String,
+    #[serde(default, deserialize_with = "super::common::null_to_default")]
+    pub dependencies: Vec<String>,
+
+    #[serde(flatten)]
+    pub extra: Map<String, Value>,
+}