diff --git a/.github/workflows/sdk-spec.yml b/.github/workflows/sdk-spec.yml
new file mode 100644
index 0000000..1f19dbb
--- /dev/null
+++ b/.github/workflows/sdk-spec.yml
@@ -0,0 +1,17 @@
+name: SDK spec
+
+on:
+  pull_request:
+  push:
+    branches: [main]
+
+permissions:
+  contents: read
+
+jobs:
+  sdk-spec:
+    # Keep the ref in `uses:` and `spec-ref` in sync.
+    uses: Flagsmith/sdk-spec/.github/workflows/run-spec.yml@v0.3.0
+    with:
+      spec-ref: v0.3.0
+      language: rust
diff --git a/Cargo.toml b/Cargo.toml
index 4e4476d..d7e7ea8 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -11,6 +11,8 @@ readme = "README.md"
 categories = ["config", "api-bindings"]
 keywords = ["Flagsmith", "feature-flag", "remote-config"]
 rust-version = "1.86.0"
+# The SDK spec steps are a separate crate used only in CI.
+exclude = ["/sdk-spec"]
 
 # See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
 
diff --git a/renovate.json b/renovate.json
index 5464e80..b674be3 100644
--- a/renovate.json
+++ b/renovate.json
@@ -3,6 +3,15 @@
     "extends": ["config:recommended", ":semanticCommitScopeDisabled"],
     "ignorePresets": [":semanticPrefixFixDepsChoreOthers"],
     "semanticCommitType": "deps",
+    "customManagers": [
+        {
+            "customType": "regex",
+            "managerFilePatterns": ["/^\\.github/workflows/sdk-spec\\.yml$/"],
+            "matchStrings": ["spec-ref: (?<currentValue>v[\\d.]+)"],
+            "depNameTemplate": "Flagsmith/sdk-spec",
+            "datasourceTemplate": "github-tags"
+        }
+    ],
     "packageRules": [
         {
             "matchUpdateTypes": [
@@ -21,6 +30,11 @@
         {
             "matchPackageNames": ["flagsmith-flag-engine"],
             "enabled": true
+        },
+        {
+            "matchPackageNames": ["Flagsmith/sdk-spec"],
+            "groupName": "SDK spec",
+            "enabled": true
         }
     ]
 }
diff --git a/sdk-spec/.gitignore b/sdk-spec/.gitignore
new file mode 100644
index 0000000..4fffb2f
--- /dev/null
+++ b/sdk-spec/.gitignore
@@ -0,0 +1,2 @@
+/target
+/Cargo.lock
diff --git a/sdk-spec/Cargo.toml b/sdk-spec/Cargo.toml
new file mode 100644
index 0000000..73cb089
--- /dev/null
+++ b/sdk-spec/Cargo.toml
@@ -0,0 +1,14 @@
+# The steps file as a crate, built by the Rust harness of the Flagsmith SDK behavioural spec.
+[package]
+name = "sdk-spec"
+version = "0.0.0"
+edition = "2021"
+publish = false
+
+[lib]
+path = "steps.rs"
+
+[dependencies]
+flagsmith = { path = ".." }
+flagsmith-flag-engine = "0.6"
+serde = { version = "1.0", features = ["derive"] }
diff --git a/sdk-spec/Dockerfile b/sdk-spec/Dockerfile
new file mode 100644
index 0000000..658ca09
--- /dev/null
+++ b/sdk-spec/Dockerfile
@@ -0,0 +1,23 @@
+# Runs this SDK, built from source, under the Flagsmith SDK behavioural spec.
+# docker build -f sdk-spec/Dockerfile --build-context harness=<sdk-spec>/harness/rust .
+FROM docker.io/library/rust:1.86-slim-bookworm AS build
+
+WORKDIR /sdk
+COPY Cargo.toml Cargo.lock README.md ./
+COPY src ./src
+COPY sdk-spec/Cargo.toml sdk-spec/steps.rs ./sdk-spec/
+
+# The harness builds the steps file in, from the SDK checkout at /sdk.
+COPY --from=harness . /harness
+# Resolve dependencies to the versions the SDK is tested with.
+COPY Cargo.lock /harness/Cargo.lock
+RUN cargo build --release --manifest-path /harness/Cargo.toml
+
+FROM docker.io/library/debian:bookworm-slim
+# The SDK's HTTP client fails to build without system CA certificates.
+RUN apt-get update \
+    && apt-get install -y --no-install-recommends ca-certificates \
+    && rm -rf /var/lib/apt/lists/*
+COPY --from=build /harness/target/release/sdk-spec-harness /usr/local/bin/
+
+ENTRYPOINT ["sdk-spec-harness"]
diff --git a/sdk-spec/steps.rs b/sdk-spec/steps.rs
new file mode 100644
index 0000000..52321ce
--- /dev/null
+++ b/sdk-spec/steps.rs
@@ -0,0 +1,59 @@
+//! Steps for the Flagsmith SDK behavioural spec: https://github.com/Flagsmith/sdk-spec
+//!
+//! Each function implements the Gherkin step in the comment above it.
+
+use std::collections::HashMap;
+
+use flagsmith::error::Error;
+use flagsmith::flagsmith::models::{Flags, SDKTrait};
+use flagsmith::{Flagsmith, FlagsmithOptions};
+use flagsmith_flag_engine::types::FlagsmithValue;
+use serde::Serialize;
+
+#[derive(Serialize)]
+pub struct SpecFlag {
+    feature: String,
+    enabled: bool,
+    value: FlagsmithValue,
+}
+
+fn as_spec_flags(flags: Flags) -> Vec<SpecFlag> {
+    flags
+        .all_flags()
+        .into_iter()
+        .map(|flag| SpecFlag {
+            feature: flag.feature_name,
+            enabled: flag.enabled,
+            value: flag.value,
+        })
+        .collect()
+}
+
+// Create the SDK client
+pub fn create_client(environment_key: String, api_url: String) -> Flagsmith {
+    let options = FlagsmithOptions {
+        api_url,
+        ..Default::default()
+    };
+    Flagsmith::new(environment_key, options)
+}
+
+// When the application gets the environment flags
+pub fn get_environment_flags(flagsmith: &Flagsmith) -> Result<Vec<SpecFlag>, Error> {
+    flagsmith.get_environment_flags().map(as_spec_flags)
+}
+
+// When the application gets the flags for identity "{identifier}" with traits:
+pub fn get_identity_flags(
+    flagsmith: &Flagsmith,
+    identifier: String,
+    traits: HashMap<String, FlagsmithValue>,
+) -> Result<Vec<SpecFlag>, Error> {
+    let traits = traits
+        .into_iter()
+        .map(|(key, value)| SDKTrait::new(key, value))
+        .collect();
+    flagsmith
+        .get_identity_flags(&identifier, Some(traits), None)
+        .map(as_spec_flags)
+}