diff --git a/Cargo.toml b/Cargo.toml
index ab5854d..7b1fc8f 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -55,6 +55,7 @@ log = "0.4.14"
 murmur3 = "0.5.1"
 rand = "0.8.4"
 rustversion = "1.0.7"
+semver = "1.0.18"
 serde_json = "1.0.68"
 serde_plain = "1.0.0"
 surf = { version = "2.3.1", optional = true }
diff --git a/README.md b/README.md
index 1093f49..d4cff54 100644
--- a/README.md
+++ b/README.md
@@ -107,4 +107,4 @@ UNLEASH_API_URL=http://127.0.0.1:4242/api \
 
 or similar. The functional test suite looks for a manually setup set of
 features. E.g. log into the Unleash UI on port 4242 and create a feature called
-`default`.
+`default` & `semver` with a `SEMVER_EQ` strategy constraint.
diff --git a/docker-compose.yml b/docker-compose.yml
index 3510ec1..0771287 100644
--- a/docker-compose.yml
+++ b/docker-compose.yml
@@ -1,7 +1,7 @@
 version: "3.3"
 services:
   web:
-    image: unleashorg/unleash-server:4.12.6
+    image: unleashorg/unleash-server:4.16.0
     ports:
       - "4242:4242"
     environment:
diff --git a/src/api.rs b/src/api.rs
index a0babdb..078ccf5 100644
--- a/src/api.rs
+++ b/src/api.rs
@@ -50,13 +50,29 @@ pub struct Constraint {
 }
 
 #[derive(Clone, Serialize, Deserialize, Debug)]
-#[serde(tag = "operator", content = "values")]
+#[serde(tag = "operator")]
 #[cfg_attr(feature = "strict", serde(deny_unknown_fields))]
 pub enum ConstraintExpression {
     #[serde(rename = "IN")]
-    In(Vec<String>),
+    In(MultiValueExpression),
     #[serde(rename = "NOT_IN")]
-    NotIn(Vec<String>),
+    NotIn(MultiValueExpression),
+    #[serde(rename = "SEMVER_EQ")]
+    SemverEq(SingleValueExpression),
+    #[serde(rename = "SEMVER_GT")]
+    SemverGt(SingleValueExpression),
+    #[serde(rename = "SEMVER_LT")]
+    SemverLt(SingleValueExpression),
+}
+
+#[derive(Clone, Serialize, Deserialize, Debug)]
+pub struct MultiValueExpression {
+    pub values: Vec<String>,
+}
+
+#[derive(Clone, Serialize, Deserialize, Debug)]
+pub struct SingleValueExpression {
+    pub value: String,
 }
 
 #[derive(Clone, Serialize, Deserialize, Debug)]
diff --git a/src/client.rs b/src/client.rs
index 654f22a..7f6ecea 100644
--- a/src/client.rs
+++ b/src/client.rs
@@ -777,10 +777,9 @@ where
         self.polling.store(true, Ordering::Relaxed);
         loop {
             debug!("poll: retrieving features");
-            let res = self.http.get_json(&endpoint).await;
-            if let Ok(res) = res {
-                let features: Features = res;
-                match self.memoize(features.features) {
+            let res: Result<Features, C::Error> = self.http.get_json(&endpoint).await;
+            match res {
+                Ok(features) => match self.memoize(features.features) {
                     Ok(None) => {}
                     Ok(Some(metrics)) => {
                         if !self.disable_metric_submission {
@@ -800,9 +799,10 @@ where
                     Err(_) => {
                         warn!("poll: failed to memoize features");
                     }
+                },
+                Err(err) => {
+                    warn!("poll: failed to retrieve features {}", err);
                 }
-            } else {
-                warn!("poll: failed to retrieve features");
             }
 
             let duration = Duration::from_millis(self.interval);
diff --git a/src/strategy.rs b/src/strategy.rs
index b8d82ca..b4caa71 100644
--- a/src/strategy.rs
+++ b/src/strategy.rs
@@ -10,8 +10,9 @@ use ipnet::IpNet;
 use log::{trace, warn};
 use murmur3::murmur3_32;
 use rand::Rng;
+use semver::{Version, VersionReq};
 
-use crate::api::{Constraint, ConstraintExpression};
+use crate::api::{Constraint, ConstraintExpression, MultiValueExpression, SingleValueExpression};
 use crate::context::Context;
 
 /// Memoise feature state for a strategy.
@@ -296,13 +297,13 @@ where
     F: Fn(&Context) -> Option<&String> + Clone + Sync + Send + 'static,
 {
     match &expression {
-        ConstraintExpression::In(values) => {
+        ConstraintExpression::In(MultiValueExpression { values, .. }) => {
             let as_set: HashSet<String> = values.iter().cloned().collect();
             Box::new(move |context: &Context| {
                 getter(context).map(|v| as_set.contains(v)).unwrap_or(false)
             })
         }
-        ConstraintExpression::NotIn(values) => {
+        ConstraintExpression::NotIn(MultiValueExpression { values, .. }) => {
             if values.is_empty() {
                 Box::new(|_| true)
             } else {
@@ -314,6 +315,39 @@ where
                 })
             }
         }
+        ConstraintExpression::SemverEq(SingleValueExpression { value, .. }) => {
+            evaluate_semver_expression(getter, &format!("={value}"))
+        }
+        ConstraintExpression::SemverGt(SingleValueExpression { value, .. }) => {
+            evaluate_semver_expression(getter, &format!(">{value}"))
+        }
+        ConstraintExpression::SemverLt(SingleValueExpression { value, .. }) => {
+            evaluate_semver_expression(getter, &format!("<{value}"))
+        }
+    }
+}
+
+fn evaluate_semver_expression<F>(
+    getter: F,
+    version_req: &str,
+) -> Box<dyn Evaluator + Send + Sync + 'static>
+where
+    F: Fn(&Context) -> Option<&String> + Clone + Sync + Send + 'static,
+{
+    let parsed_request = VersionReq::parse(version_req);
+    match parsed_request {
+        Ok(req) => Box::new(move |context: &Context| {
+            getter(context)
+                .map(|v: &String| {
+                    let parsed = Version::parse(v);
+                    match parsed {
+                        Ok(version) => req.matches(&version),
+                        _ => false,
+                    }
+                })
+                .unwrap_or(false)
+        }),
+        _ => Box::new(|_| false),
     }
 }
 
@@ -336,7 +370,7 @@ where
     F: Fn(&Context) -> Option<&crate::context::IPAddress> + Clone + Sync + Send + 'static,
 {
     match &expression {
-        ConstraintExpression::In(values) => {
+        ConstraintExpression::In(MultiValueExpression { values, .. }) => {
             let ips = _ip_to_vec(values);
             Box::new(move |context: &Context| {
                 getter(context)
@@ -351,7 +385,7 @@ where
                     .unwrap_or(false)
             })
         }
-        ConstraintExpression::NotIn(values) => {
+        ConstraintExpression::NotIn(MultiValueExpression { values }) => {
             if values.is_empty() {
                 Box::new(|_| false)
             } else {
@@ -373,6 +407,7 @@ where
                 })
             }
         }
+        _ => Box::new(|_| false),
     }
 }
 
@@ -452,7 +487,7 @@ mod tests {
 
     use maplit::hashmap;
 
-    use crate::api::{Constraint, ConstraintExpression};
+    use crate::api::{Constraint, ConstraintExpression, MultiValueExpression};
     use crate::context::{Context, IPAddress};
 
     fn parse_ip(addr: &str) -> Option<IPAddress> {
@@ -479,7 +514,7 @@ mod tests {
         assert!(!super::constrain(
             Some(vec![Constraint {
                 context_name: "".into(),
-                expression: ConstraintExpression::In(vec![]),
+                expression: ConstraintExpression::In(MultiValueExpression { values: vec![] }),
             }]),
             &super::default,
             None
@@ -493,7 +528,9 @@ mod tests {
         assert!(!super::constrain(
             Some(vec![Constraint {
                 context_name: "environment".into(),
-                expression: ConstraintExpression::In(vec!["development".into()]),
+                expression: ConstraintExpression::In(MultiValueExpression {
+                    values: vec!["development".into()]
+                }),
             }]),
             &super::default,
             None
@@ -507,7 +544,9 @@ mod tests {
         assert!(!super::constrain(
             Some(vec![Constraint {
                 context_name: "environment".into(),
-                expression: ConstraintExpression::NotIn(vec!["development".into()]),
+                expression: ConstraintExpression::NotIn(MultiValueExpression {
+                    values: vec!["development".into()]
+                }),
             }]),
             &super::default,
             None
@@ -521,7 +560,9 @@ mod tests {
         assert!(super::constrain(
             Some(vec![Constraint {
                 context_name: "environment".into(),
-                expression: ConstraintExpression::In(vec!["development".into()]),
+                expression: ConstraintExpression::In(MultiValueExpression {
+                    values: vec!["development".into()]
+                }),
             }]),
             &super::default,
             None
@@ -534,7 +575,9 @@ mod tests {
         assert!(super::constrain(
             Some(vec![Constraint {
                 context_name: "environment".into(),
-                expression: ConstraintExpression::In(vec!["staging".into(), "development".into()]),
+                expression: ConstraintExpression::In(MultiValueExpression {
+                    values: vec!["staging".into(), "development".into()]
+                }),
             }]),
             &super::default,
             None
@@ -548,10 +591,9 @@ mod tests {
         assert!(super::constrain(
             Some(vec![Constraint {
                 context_name: "environment".into(),
-                expression: ConstraintExpression::NotIn(vec![
-                    "staging".into(),
-                    "development".into()
-                ]),
+                expression: ConstraintExpression::NotIn(MultiValueExpression {
+                    values: vec!["staging".into(), "development".into()]
+                }),
             }]),
             &super::default,
             None
@@ -567,7 +609,9 @@ mod tests {
         assert!(super::constrain(
             Some(vec![Constraint {
                 context_name: "userId".into(),
-                expression: ConstraintExpression::In(vec!["fred".into()]),
+                expression: ConstraintExpression::In(MultiValueExpression {
+                    values: vec!["fred".into()]
+                }),
             }]),
             &super::default,
             None
@@ -581,7 +625,9 @@ mod tests {
         assert!(super::constrain(
             Some(vec![Constraint {
                 context_name: "sessionId".into(),
-                expression: ConstraintExpression::In(vec!["qwerty".into()]),
+                expression: ConstraintExpression::In(MultiValueExpression {
+                    values: vec!["qwerty".into()]
+                }),
             }]),
             &super::default,
             None
@@ -595,7 +641,9 @@ mod tests {
         assert!(super::constrain(
             Some(vec![Constraint {
                 context_name: "remoteAddress".into(),
-                expression: ConstraintExpression::In(vec!["10.0.0.0/8".into()]),
+                expression: ConstraintExpression::In(MultiValueExpression {
+                    values: vec!["10.0.0.0/8".into()]
+                }),
             }]),
             &super::default,
             None
@@ -607,7 +655,9 @@ mod tests {
         assert!(super::constrain(
             Some(vec![Constraint {
                 context_name: "remoteAddress".into(),
-                expression: ConstraintExpression::NotIn(vec!["10.0.0.0/8".into()]),
+                expression: ConstraintExpression::NotIn(MultiValueExpression {
+                    values: vec!["10.0.0.0/8".into()]
+                }),
             }]),
             &super::default,
             None
@@ -623,11 +673,15 @@ mod tests {
             Some(vec![
                 Constraint {
                     context_name: "environment".into(),
-                    expression: ConstraintExpression::In(vec!["development".into()]),
+                    expression: ConstraintExpression::In(MultiValueExpression {
+                        values: vec!["development".into()]
+                    }),
                 },
                 Constraint {
                     context_name: "environment".into(),
-                    expression: ConstraintExpression::In(vec!["development".into()]),
+                    expression: ConstraintExpression::In(MultiValueExpression {
+                        values: vec!["development".into()]
+                    }),
                 },
             ]),
             &super::default,
@@ -637,11 +691,13 @@ mod tests {
             Some(vec![
                 Constraint {
                     context_name: "environment".into(),
-                    expression: ConstraintExpression::In(vec!["development".into()]),
+                    expression: ConstraintExpression::In(MultiValueExpression {
+                        values: vec!["development".into()]
+                    }),
                 },
                 Constraint {
                     context_name: "environment".into(),
-                    expression: ConstraintExpression::In(vec![]),
+                    expression: ConstraintExpression::In(MultiValueExpression { values: vec![] }),
                 }
             ]),
             &super::default,
@@ -649,6 +705,106 @@ mod tests {
         )(&context));
     }
 
+    #[test]
+    fn test_semver_constrain() {
+        let context = Context {
+            properties: hashmap! {
+                "version".to_string() => "1.1.1".to_string()
+            },
+            ..Default::default()
+        };
+        assert!(super::constrain(
+            Some(vec![Constraint {
+                context_name: "version".into(),
+                expression: ConstraintExpression::SemverEq(crate::api::SingleValueExpression {
+                    value: "1.1.1".to_string()
+                }),
+            }]),
+            &super::default,
+            None
+        )(&context));
+        assert!(!super::constrain(
+            Some(vec![Constraint {
+                context_name: "version".into(),
+                expression: ConstraintExpression::SemverEq(crate::api::SingleValueExpression {
+                    value: "1.0.1".to_string()
+                }),
+            }]),
+            &super::default,
+            None
+        )(&context));
+        assert!(super::constrain(
+            Some(vec![Constraint {
+                context_name: "version".into(),
+                expression: ConstraintExpression::SemverGt(crate::api::SingleValueExpression {
+                    value: "1.0.0".to_string()
+                }),
+            }]),
+            &super::default,
+            None
+        )(&context));
+        assert!(super::constrain(
+            Some(vec![Constraint {
+                context_name: "version".into(),
+                expression: ConstraintExpression::SemverGt(crate::api::SingleValueExpression {
+                    value: "1.1.0".to_string()
+                }),
+            }]),
+            &super::default,
+            None
+        )(&context));
+        assert!(!super::constrain(
+            Some(vec![Constraint {
+                context_name: "version".into(),
+                expression: ConstraintExpression::SemverGt(crate::api::SingleValueExpression {
+                    value: "1.1.1".to_string()
+                }),
+            }]),
+            &super::default,
+            None
+        )(&context));
+        assert!(super::constrain(
+            Some(vec![Constraint {
+                context_name: "version".into(),
+                expression: ConstraintExpression::SemverLt(crate::api::SingleValueExpression {
+                    value: "1.1.2".to_string()
+                }),
+            }]),
+            &super::default,
+            None
+        )(&context));
+        assert!(super::constrain(
+            Some(vec![Constraint {
+                context_name: "version".into(),
+                expression: ConstraintExpression::SemverLt(crate::api::SingleValueExpression {
+                    value: "1.2.0".to_string()
+                }),
+            }]),
+            &super::default,
+            None
+        )(&context));
+        assert!(super::constrain(
+            Some(vec![Constraint {
+                context_name: "version".into(),
+                expression: ConstraintExpression::SemverLt(crate::api::SingleValueExpression {
+                    value: "2.0.0".to_string()
+                }),
+            }]),
+            &super::default,
+            None
+        )(&context));
+        assert!(!super::constrain(
+            Some(vec![Constraint {
+                context_name: "version".into(),
+                expression: ConstraintExpression::SemverLt(crate::api::SingleValueExpression {
+                    value: "1.0.0".to_string()
+                }),
+            }]),
+            &super::default,
+            None
+        )(&context));
+    }
+
     #[test]
     fn test_user_with_id() {
         let params: HashMap<String, String> = hashmap! {
diff --git a/tests/functional.rs b/tests/functional.rs
index 4c08665..c1bba96 100644
--- a/tests/functional.rs
+++ b/tests/functional.rs
@@ -19,6 +19,7 @@ mod tests {
     use futures_timer::Delay;
     use serde::{Deserialize, Serialize};
 
+    use unleash_api_client::Context;
     use unleash_api_client::{client, config::EnvironmentConfig, http::HttpClient};
 
     #[cfg(not(any(feature = "surf", feature = "reqwest")))]
@@ -28,6 +29,7 @@ mod tests {
     #[derive(Debug, Deserialize, Serialize, Enum, Clone)]
     enum UserFeatures {
         default,
+        semver
     }
 
     #[async_trait]
@@ -120,6 +122,7 @@ mod tests {
             // Ensure we have features
             Delay::new(Duration::from_millis(500)).await;
             assert!(client.is_enabled(UserFeatures::default, None, false));
+            assert!(client.is_enabled(UserFeatures::semver, Some(&Context { app_name: "1.0.0".to_string(), ..Context::default() }), false));
             // Ensure the metrics get up-loaded
             Delay::new(Duration::from_millis(500)).await;
             client.stop_poll().await;
@@ -179,7 +182,7 @@ mod tests {
         A::sleep(Duration::from_millis(500)).await;
         assert!(client.is_enabled(UserFeatures::default, None, false));
         // Ensure the metrics get up-loaded
-        A::sleep(Duration::from_millis(500));
+        let _ = A::sleep(Duration::from_millis(500));
         client.stop_poll().await;
 
         handler.await;