diff --git a/Cargo.lock b/Cargo.lock
index 8c907e3516..c72d21f76d 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -4209,6 +4209,7 @@ dependencies = [
 name = "goose-acp"
 version = "1.23.0"
 dependencies = [
+ "agent-client-protocol-schema",
  "anyhow",
  "assert-json-diff",
  "async-stream",
diff --git a/crates/goose-acp/Cargo.toml b/crates/goose-acp/Cargo.toml
index 135f2f0b45..507df29a6f 100644
--- a/crates/goose-acp/Cargo.toml
+++ b/crates/goose-acp/Cargo.toml
@@ -19,6 +19,7 @@ goose = { path = "../goose" }
 goose-mcp = { path = "../goose-mcp" }
 rmcp = { workspace = true }
 sacp = "10.1.0"
+agent-client-protocol-schema = { version = "0.10", features = ["unstable_session_model"] }
 anyhow = { workspace = true }
 tokio = { workspace = true }
 tokio-util = { version = "0.7.15", features = ["compat", "rt"] }
diff --git a/crates/goose-acp/src/server.rs b/crates/goose-acp/src/server.rs
index 3f344914cb..59bdbc23bf 100644
--- a/crates/goose-acp/src/server.rs
+++ b/crates/goose-acp/src/server.rs
@@ -13,6 +13,7 @@ use goose::conversation::Conversation;
 use goose::mcp_utils::ToolResult;
 use goose::permission::permission_confirmation::PrincipalType;
 use goose::permission::{Permission, PermissionConfirmation};
+use goose::providers::base::Provider;
 use goose::providers::provider_registry::ProviderConstructor;
 use goose::session::session_manager::SessionType;
 use goose::session::{Session, SessionManager};
@@ -21,12 +22,13 @@ use sacp::schema::{
     AgentCapabilities, AuthMethod, AuthenticateRequest, AuthenticateResponse, BlobResourceContents,
     CancelNotification, Content, ContentBlock, ContentChunk, EmbeddedResource,
     EmbeddedResourceResource, ImageContent, InitializeRequest, InitializeResponse,
-    LoadSessionRequest, LoadSessionResponse, McpCapabilities, McpServer, NewSessionRequest,
-    NewSessionResponse, PermissionOption, PermissionOptionKind, PromptCapabilities, PromptRequest,
-    PromptResponse, RequestPermissionOutcome, RequestPermissionRequest, ResourceLink, SessionId,
-    SessionNotification, SessionUpdate, StopReason, TextContent, TextResourceContents, ToolCall,
-    ToolCallContent, ToolCallId, ToolCallLocation, ToolCallStatus, ToolCallUpdate,
-    ToolCallUpdateFields, ToolKind,
+    LoadSessionRequest, LoadSessionResponse, McpCapabilities, McpServer, ModelId, ModelInfo,
+    NewSessionRequest, NewSessionResponse, PermissionOption, PermissionOptionKind,
+    PromptCapabilities, PromptRequest, PromptResponse, RequestPermissionOutcome,
+    RequestPermissionRequest, ResourceLink, SessionId, SessionModelState, SessionNotification,
+    SessionUpdate, SetSessionModelRequest, SetSessionModelResponse, StopReason, TextContent,
+    TextResourceContents, ToolCall, ToolCallContent, ToolCallId, ToolCallLocation, ToolCallStatus,
+    ToolCallUpdate, ToolCallUpdateFields, ToolKind,
 };
 use sacp::{AgentToClient, ByteStreams, Handled, JrConnectionCx, JrMessageHandler, MessageCx};
 use std::collections::HashMap;
@@ -48,7 +50,7 @@ pub struct GooseAcpAgent {
     agent: Arc<Agent>,
     provider_factory: ProviderConstructor,
     config_dir: std::path::PathBuf,
-    provider_initialized: tokio::sync::OnceCell<String>,
+    provider_initialized: tokio::sync::OnceCell<Arc<dyn Provider>>,
 }
 
 fn mcp_server_to_extension_config(mcp_server: McpServer) -> Result<ExtensionConfig, String> {
@@ -266,6 +268,22 @@ async fn add_extensions(agent: &Agent, extensions: Vec<ExtensionConfig>) {
     }
 }
 
+async fn build_model_state(
+    provider: &dyn Provider,
+    current_model: &str,
+) -> Result<SessionModelState, sacp::Error> {
+    let models = provider.fetch_recommended_models().await.map_err(|e| {
+        sacp::Error::internal_error().data(format!("Failed to fetch models: {}", e))
+    })?;
+    Ok(SessionModelState::new(
+        ModelId::new(current_model),
+        models
+            .iter()
+            .map(|name| ModelInfo::new(ModelId::new(&**name), &**name))
+            .collect(),
+    ))
+}
+
 impl GooseAcpAgent {
     pub fn permission_manager(&self) -> Arc<PermissionManager> {
         Arc::clone(&self.agent.config.permission_manager)
@@ -682,7 +700,7 @@ impl GooseAcpAgent {
             .map_err(|e| {
                 sacp::Error::internal_error().data(format!("Failed to create session: {}", e))
             })?;
-        self.ensure_provider(&goose_session).await.map_err(|e| {
+        let provider = self.ensure_provider(&goose_session).await.map_err(|e| {
             sacp::Error::internal_error().data(format!("Failed to set provider: {}", e))
         })?;
 
@@ -715,25 +733,28 @@ impl GooseAcpAgent {
             "Session started"
         );
 
-        Ok(NewSessionResponse::new(SessionId::new(goose_session.id)))
+        let model_state =
+            build_model_state(&**provider, &provider.get_model_config().model_name).await?;
+
+        Ok(NewSessionResponse::new(SessionId::new(goose_session.id)).models(model_state))
     }
 
-    // Called at most once via OnceCell; returns the model_id used.
-    async fn create_provider(&self, session: &Session) -> Result<String> {
+    async fn create_provider(&self, session: &Session) -> Result<Arc<dyn Provider>> {
         let config_path = self.config_dir.join(CONFIG_YAML_NAME);
         let config = Config::new(&config_path, "goose")?;
         let model_id = config.get_goose_model()?;
         let model_config = goose::model::ModelConfig::new(&model_id)?;
         let provider = (self.provider_factory)(model_config).await?;
-        self.agent.update_provider(provider, &session.id).await?;
-        Ok(model_id)
+        self.agent
+            .update_provider(provider.clone(), &session.id)
+            .await?;
+        Ok(provider)
     }
 
-    async fn ensure_provider(&self, session: &Session) -> Result<()> {
+    async fn ensure_provider(&self, session: &Session) -> Result<&Arc<dyn Provider>> {
         self.provider_initialized
             .get_or_try_init(|| self.create_provider(session))
-            .await?;
-        Ok(())
+            .await
     }
 
     async fn on_load_session(
@@ -750,7 +771,7 @@ impl GooseAcpAgent {
             sacp::Error::invalid_params()
                 .data(format!("Failed to load session {}: {}", session_id, e))
         })?;
-        self.ensure_provider(&goose_session).await.map_err(|e| {
+        let provider = self.ensure_provider(&goose_session).await.map_err(|e| {
             sacp::Error::internal_error().data(format!("Failed to set provider: {}", e))
         })?;
 
@@ -830,7 +851,10 @@ impl GooseAcpAgent {
             "Session loaded"
         );
 
-        Ok(LoadSessionResponse::new())
+        let model_state =
+            build_model_state(&**provider, &provider.get_model_config().model_name).await?;
+
+        Ok(LoadSessionResponse::new().models(model_state))
     }
 
     async fn on_prompt(
@@ -928,6 +952,28 @@ impl GooseAcpAgent {
 
         Ok(())
     }
+
+    async fn on_set_model(
+        &self,
+        session_id: &str,
+        model_id: &str,
+    ) -> Result<SetSessionModelResponse, sacp::Error> {
+        let model_config = goose::model::ModelConfig::new(model_id).map_err(|e| {
+            sacp::Error::internal_error().data(format!("Invalid model config: {}", e))
+        })?;
+        let provider = (self.provider_factory)(model_config).await.map_err(|e| {
+            sacp::Error::internal_error().data(format!("Failed to create provider: {}", e))
+        })?;
+        self.agent
+            .update_provider(provider, session_id)
+            .await
+            .map_err(|e| {
+                sacp::Error::internal_error().data(format!("Failed to update provider: {}", e))
+            })?;
+
+        info!(session_id = %session_id, model_id = %model_id, "Model switched");
+        Ok(SetSessionModelResponse::new())
+    }
 }
 
 pub struct GooseAcpHandler {
@@ -997,7 +1043,30 @@ impl JrMessageHandler for GooseAcpHandler {
                 self.agent.on_cancel(notif).await
             })
             .await
-            .done()
+            // HACK: sacp doesn't support session/set_model yet, so we handle it as untyped JSON.
+            .otherwise({
+                let agent = self.agent.clone();
+                |message: MessageCx| async move {
+                    match message {
+                        MessageCx::Request(req, request_cx)
+                            if req.method == "session/set_model" =>
+                        {
+                            let params: SetSessionModelRequest = serde_json::from_value(req.params)
+                                .map_err(|e| sacp::Error::invalid_params().data(e.to_string()))?;
+                            let resp = agent
+                                .on_set_model(&params.session_id.0, &params.model_id.0)
+                                .await?;
+                            let json = serde_json::to_value(resp)
+                                .map_err(|e| sacp::Error::internal_error().data(e.to_string()))?;
+                            request_cx.respond(json)?;
+                            Ok(())
+                        }
+                        _ => Err(sacp::Error::method_not_found()),
+                    }
+                }
+            })
+            .await
+            .map(|()| Handled::Yes)
     }
 }
 
@@ -1189,4 +1258,79 @@ print(\"hello, world\")
     ) {
         assert_eq!(outcome_to_confirmation(&input), expected);
     }
+
+    use goose::providers::errors::ProviderError;
+
+    struct MockModelProvider {
+        models: Result<Vec<String>, ProviderError>,
+    }
+
+    #[async_trait::async_trait]
+    impl goose::providers::base::Provider for MockModelProvider {
+        fn get_name(&self) -> &str {
+            "mock"
+        }
+
+        async fn complete_with_model(
+            &self,
+            _session_id: Option<&str>,
+            _model_config: &goose::model::ModelConfig,
+            _system: &str,
+            _messages: &[goose::conversation::message::Message],
+            _tools: &[rmcp::model::Tool],
+        ) -> Result<
+            (
+                goose::conversation::message::Message,
+                goose::providers::base::ProviderUsage,
+            ),
+            ProviderError,
+        > {
+            unimplemented!()
+        }
+
+        fn get_model_config(&self) -> goose::model::ModelConfig {
+            goose::model::ModelConfig::new_or_fail("unused")
+        }
+
+        async fn fetch_recommended_models(&self) -> Result<Vec<String>, ProviderError> {
+            self.models.clone()
+        }
+    }
+
+    #[test_case(
+        "model-a", Ok(vec!["model-a".into(), "model-b".into()])
+        => Ok(SessionModelState::new(
+            ModelId::new("model-a"),
+            vec![ModelInfo::new(ModelId::new("model-a"), "model-a"),
+                 ModelInfo::new(ModelId::new("model-b"), "model-b")],
+        ))
+        ; "returns current and available models"
+    )]
+    #[test_case(
+        "model-a", Ok(vec![])
+        => Ok(SessionModelState::new(ModelId::new("model-a"), vec![]))
+        ; "empty model list"
+    )]
+    #[test_case(
+        "model-a", Err(ProviderError::ExecutionError("fail".into()))
+        => matches Err(_)
+        ; "fetch error propagates"
+    )]
+    #[test_case(
+        "switched-model", Ok(vec!["model-a".into(), "switched-model".into()])
+        => Ok(SessionModelState::new(
+            ModelId::new("switched-model"),
+            vec![ModelInfo::new(ModelId::new("model-a"), "model-a"),
+                 ModelInfo::new(ModelId::new("switched-model"), "switched-model")],
+        ))
+        ; "current model reflects switched model"
+    )]
+    #[tokio::test]
+    async fn test_build_model_state(
+        current_model: &str,
+        models: Result<Vec<String>, ProviderError>,
+    ) -> Result<SessionModelState, sacp::Error> {
+        let provider = MockModelProvider { models };
+        build_model_state(&provider, current_model).await
+    }
 }
diff --git a/crates/goose-acp/tests/common_tests/mod.rs b/crates/goose-acp/tests/common_tests/mod.rs
index e1d8ba53cc..e2e1130421 100644
--- a/crates/goose-acp/tests/common_tests/mod.rs
+++ b/crates/goose-acp/tests/common_tests/mod.rs
@@ -8,8 +8,10 @@ use fixtures::{OpenAiFixture, PermissionDecision, Session, TestSessionConfig};
 use fs_err as fs;
 use goose::config::base::CONFIG_YAML_NAME;
 use goose::config::GooseMode;
-use goose_test_support::{ExpectedSessionId, McpFixture, FAKE_CODE};
-use sacp::schema::{McpServer, McpServerHttp, ToolCallStatus};
+use goose_test_support::{ExpectedSessionId, McpFixture, FAKE_CODE, TEST_MODEL};
+use sacp::schema::{
+    McpServer, McpServerHttp, ModelId, ModelInfo, SessionModelState, ToolCallStatus,
+};
 
 pub async fn run_config_mcp<S: Session>() {
     let temp_dir = tempfile::tempdir().unwrap();
@@ -18,7 +20,7 @@ pub async fn run_config_mcp<S: Session>() {
     let mcp = McpFixture::new(Some(expected_session_id.clone())).await;
 
     let config_yaml = format!(
-        "GOOSE_MODEL: gpt-5-nano\nextensions:\n  mcp-fixture:\n    enabled: true\n    type: streamable_http\n    name: mcp-fixture\n    description: MCP fixture\n    uri: \"{}\"\n",
+        "GOOSE_MODEL: {TEST_MODEL}\nextensions:\n  mcp-fixture:\n    enabled: true\n    type: streamable_http\n    name: mcp-fixture\n    description: MCP fixture\n    uri: \"{}\"\n",
         mcp.url
     );
     fs::write(temp_dir.path().join(CONFIG_YAML_NAME), config_yaml).unwrap();
@@ -255,3 +257,101 @@ pub async fn run_prompt_mcp<S: Session>() {
     assert_eq!(output.text, FAKE_CODE);
     expected_session_id.assert_matches(&session.id().0);
 }
+
+pub async fn run_model_list<S: Session>() {
+    let expected_session_id = ExpectedSessionId::default();
+    let openai = OpenAiFixture::new(vec![], expected_session_id.clone()).await;
+
+    let session = S::new(TestSessionConfig::default(), openai).await;
+    expected_session_id.set(session.id().0.to_string());
+
+    let models = session.models().unwrap();
+    let expected = SessionModelState::new(
+        ModelId::new(TEST_MODEL),
+        [
+            "gpt-5.2",
+            "gpt-5.2-2025-12-11",
+            "gpt-5.2-chat-latest",
+            "gpt-5.2-codex",
+            "gpt-5.2-pro",
+            "gpt-5.2-pro-2025-12-11",
+            "gpt-5.1",
+            "gpt-5.1-2025-11-13",
+            "gpt-5.1-chat-latest",
+            "gpt-5.1-codex",
+            "gpt-5.1-codex-max",
+            "gpt-5.1-codex-mini",
+            "gpt-5-pro",
+            "gpt-5-pro-2025-10-06",
+            "gpt-5-codex",
+            "gpt-5",
+            "gpt-5-2025-08-07",
+            "gpt-5-chat-latest",
+            "gpt-5-mini",
+            "gpt-5-mini-2025-08-07",
+            TEST_MODEL,
+            "gpt-5-nano-2025-08-07",
+            "codex-mini-latest",
+            "o3",
+            "o3-2025-04-16",
+            "o4-mini",
+            "o4-mini-2025-04-16",
+            "gpt-4.1",
+            "gpt-4.1-2025-04-14",
+            "gpt-4.1-mini",
+            "gpt-4.1-mini-2025-04-14",
+            "gpt-4.1-nano",
+            "gpt-4.1-nano-2025-04-14",
+            "o1-pro",
+            "o1-pro-2025-03-19",
+            "o3-mini",
+            "o3-mini-2025-01-31",
+            "o1",
+            "o1-2024-12-17",
+            "gpt-4o",
+            "gpt-4o-2024-05-13",
+            "gpt-4o-2024-08-06",
+            "gpt-4o-2024-11-20",
+            "gpt-4o-mini",
+            "gpt-4o-mini-2024-07-18",
+            "o4-mini-deep-research",
+            "o4-mini-deep-research-2025-06-26",
+            "text-embedding-3-large",
+            "text-embedding-3-small",
+            "gpt-4",
+            "gpt-4-0613",
+            "gpt-4-turbo",
+            "gpt-4-turbo-2024-04-09",
+            "gpt-3.5-turbo",
+            "gpt-3.5-turbo-0125",
+            "gpt-3.5-turbo-1106",
+            "text-embedding-ada-002",
+        ]
+        .iter()
+        .map(|id| ModelInfo::new(ModelId::new(*id), *id))
+        .collect(),
+    );
+    assert_eq!(*models, expected);
+}
+
+pub async fn run_set_model<S: Session>() {
+    let expected_session_id = ExpectedSessionId::default();
+    let openai = OpenAiFixture::new(
+        vec![(
+            r#""model":"o4-mini""#.into(),
+            include_str!("../test_data/openai_basic.txt"),
+        )],
+        expected_session_id.clone(),
+    )
+    .await;
+
+    let mut session = S::new(TestSessionConfig::default(), openai).await;
+    expected_session_id.set(session.id().0.to_string());
+
+    session.set_model("o4-mini").await;
+
+    let output = session
+        .prompt("what is 1+1", PermissionDecision::Cancel)
+        .await;
+    assert_eq!(output.text, "2");
+}
diff --git a/crates/goose-acp/tests/fixtures/mod.rs b/crates/goose-acp/tests/fixtures/mod.rs
index a66751bf57..c5bcdbee6b 100644
--- a/crates/goose-acp/tests/fixtures/mod.rs
+++ b/crates/goose-acp/tests/fixtures/mod.rs
@@ -11,10 +11,10 @@ use goose::providers::openai::OpenAiProvider;
 use goose::providers::provider_registry::ProviderConstructor;
 use goose::session_context::SESSION_ID_HEADER;
 use goose_acp::server::{serve, GooseAcpAgent};
-use goose_test_support::ExpectedSessionId;
+use goose_test_support::{ExpectedSessionId, TEST_MODEL};
 use sacp::schema::{
     McpServer, PermissionOptionKind, RequestPermissionOutcome, RequestPermissionRequest,
-    RequestPermissionResponse, SelectedPermissionOutcome, ToolCallStatus,
+    RequestPermissionResponse, SelectedPermissionOutcome, SessionModelState, ToolCallStatus,
 };
 use std::collections::VecDeque;
 use std::future::Future;
@@ -86,6 +86,17 @@ impl OpenAiFixture {
         let mock_server = MockServer::start().await;
         let queue = Arc::new(Mutex::new(VecDeque::from(exchanges.clone())));
 
+        // Always return the models when asked, as there is no POST data to validate
+        Mock::given(method("GET"))
+            .and(path("/v1/models"))
+            .respond_with(
+                ResponseTemplate::new(200)
+                    .insert_header("content-type", "application/json")
+                    .set_body_string(include_str!("../test_data/openai_models.json")),
+            )
+            .mount(&mock_server)
+            .await;
+
         Mock::given(method("POST"))
             .and(path("/v1/chat/completions"))
             .respond_with({
@@ -188,7 +199,7 @@ pub async fn spawn_acp_server_in_process(
     // ensure_provider reads the model from config lazily, so tests need a config.yaml.
     let config_path = data_root.join(goose::config::base::CONFIG_YAML_NAME);
     if !config_path.exists() {
-        fs::write(&config_path, "GOOSE_MODEL: gpt-5-nano\n").unwrap();
+        fs::write(&config_path, format!("GOOSE_MODEL: {TEST_MODEL}\n")).unwrap();
     }
     let base_url = openai_base_url.to_string();
     let provider_factory: ProviderConstructor = Arc::new(move |model_config| {
@@ -249,9 +260,11 @@ pub trait Session {
     where
         Self: Sized;
     fn id(&self) -> &sacp::schema::SessionId;
+    fn models(&self) -> Option<&SessionModelState>;
     fn reset_openai(&self);
     fn reset_permissions(&self);
     async fn prompt(&mut self, text: &str, decision: PermissionDecision) -> TestOutput;
+    async fn set_model(&self, model_id: &str);
 }
 
 #[allow(dead_code)]
diff --git a/crates/goose-acp/tests/fixtures/server.rs b/crates/goose-acp/tests/fixtures/server.rs
index 572ebe337c..4d6a7c841d 100644
--- a/crates/goose-acp/tests/fixtures/server.rs
+++ b/crates/goose-acp/tests/fixtures/server.rs
@@ -5,9 +5,9 @@ use super::{
 use async_trait::async_trait;
 use goose::config::PermissionManager;
 use sacp::schema::{
-    ContentBlock, InitializeRequest, NewSessionRequest, PromptRequest, ProtocolVersion,
-    RequestPermissionRequest, SessionNotification, SessionUpdate, StopReason, TextContent,
-    ToolCallStatus,
+    ContentBlock, InitializeRequest, NewSessionRequest, NewSessionResponse, PromptRequest,
+    ProtocolVersion, RequestPermissionRequest, SessionModelState, SessionNotification,
+    SessionUpdate, StopReason, TextContent, ToolCallStatus,
 };
 use sacp::{ClientToAgent, JrConnectionCx};
 use std::sync::{Arc, Mutex};
@@ -17,6 +17,7 @@ use tokio::sync::Notify;
 pub struct ClientToAgentSession {
     cx: JrConnectionCx<ClientToAgent>,
     session_id: sacp::schema::SessionId,
+    new_session_response: NewSessionResponse,
     updates: Arc<Mutex<Vec<SessionNotification>>>,
     permission: Arc<Mutex<PermissionDecision>>,
     notify: Arc<Notify>,
@@ -50,7 +51,7 @@ impl Session for ClientToAgentSession {
         let notify = Arc::new(Notify::new());
         let permission = Arc::new(Mutex::new(PermissionDecision::Cancel));
 
-        let (cx, session_id) = {
+        let (cx, session_id, new_session_response) = {
             let updates_clone = updates.clone();
             let notify_clone = notify.clone();
             let permission_clone = permission.clone();
@@ -60,9 +61,12 @@ impl Session for ClientToAgentSession {
                 Arc::new(Mutex::new(None));
             let session_id_holder: Arc<Mutex<Option<sacp::schema::SessionId>>> =
                 Arc::new(Mutex::new(None));
+            let response_holder: Arc<Mutex<Option<NewSessionResponse>>> =
+                Arc::new(Mutex::new(None));
 
             let cx_holder_clone = cx_holder.clone();
             let session_id_holder_clone = session_id_holder.clone();
+            let response_holder_clone = response_holder.clone();
 
             let (ready_tx, ready_rx) = tokio::sync::oneshot::channel();
 
@@ -109,7 +113,7 @@ impl Session for ClientToAgentSession {
                                 .unwrap();
 
                             let work_dir = tempfile::tempdir().unwrap();
-                            let session = cx
+                            let response = cx
                                 .send_request(
                                     NewSessionRequest::new(work_dir.path())
                                         .mcp_servers(mcp_servers),
@@ -119,7 +123,8 @@ impl Session for ClientToAgentSession {
                                 .unwrap();
 
                             *cx_holder.lock().unwrap() = Some(cx.clone());
-                            *session_id_holder.lock().unwrap() = Some(session.session_id);
+                            *session_id_holder.lock().unwrap() = Some(response.session_id.clone());
+                            *response_holder_clone.lock().unwrap() = Some(response);
                             let _ = ready_tx.send(());
 
                             std::future::pending::<Result<(), sacp::Error>>().await
@@ -136,12 +141,14 @@ impl Session for ClientToAgentSession {
 
             let cx = cx_holder.lock().unwrap().take().unwrap();
             let session_id = session_id_holder.lock().unwrap().take().unwrap();
-            (cx, session_id)
+            let new_session_response = response_holder.lock().unwrap().take().unwrap();
+            (cx, session_id, new_session_response)
         };
 
         Self {
             cx,
             session_id,
+            new_session_response,
             updates,
             permission,
             notify,
@@ -155,6 +162,10 @@ impl Session for ClientToAgentSession {
         &self.session_id
     }
 
+    fn models(&self) -> Option<&SessionModelState> {
+        self.new_session_response.models.as_ref()
+    }
+
     fn reset_openai(&self) {
         self._openai.reset();
     }
@@ -195,6 +206,19 @@ impl Session for ClientToAgentSession {
 
         TestOutput { text, tool_status }
     }
+
+    // HACK: sacp doesn't support session/set_model yet, so we send it as untyped JSON.
+    async fn set_model(&self, model_id: &str) {
+        let msg = sacp::UntypedMessage::new(
+            "session/set_model",
+            serde_json::json!({
+                "sessionId": self.session_id.0,
+                "modelId": model_id
+            }),
+        )
+        .unwrap();
+        self.cx.send_request(msg).block_task().await.unwrap();
+    }
 }
 
 fn collect_agent_text(updates: &Arc<Mutex<Vec<SessionNotification>>>) -> String {
diff --git a/crates/goose-acp/tests/server_test.rs b/crates/goose-acp/tests/server_test.rs
index 2121a90462..c20a7074a1 100644
--- a/crates/goose-acp/tests/server_test.rs
+++ b/crates/goose-acp/tests/server_test.rs
@@ -3,8 +3,8 @@ use common_tests::fixtures::initialize_agent;
 use common_tests::fixtures::run_test;
 use common_tests::fixtures::server::ClientToAgentSession;
 use common_tests::{
-    run_config_mcp, run_permission_persistence, run_prompt_basic, run_prompt_codemode,
-    run_prompt_image, run_prompt_mcp,
+    run_config_mcp, run_model_list, run_permission_persistence, run_prompt_basic,
+    run_prompt_codemode, run_prompt_image, run_prompt_mcp, run_set_model,
 };
 use goose::config::GooseMode;
 use goose::providers::provider_registry::ProviderConstructor;
@@ -16,6 +16,16 @@ fn test_config_mcp() {
     run_test(async { run_config_mcp::<ClientToAgentSession>().await });
 }
 
+#[test]
+fn test_model_list() {
+    run_test(async { run_model_list::<ClientToAgentSession>().await });
+}
+
+#[test]
+fn test_set_model() {
+    run_test(async { run_set_model::<ClientToAgentSession>().await });
+}
+
 #[test]
 fn test_permission_persistence() {
     run_test(async { run_permission_persistence::<ClientToAgentSession>().await });
diff --git a/crates/goose-acp/tests/test_data/openai_models.json b/crates/goose-acp/tests/test_data/openai_models.json
new file mode 100644
index 0000000000..8429f3fcf5
--- /dev/null
+++ b/crates/goose-acp/tests/test_data/openai_models.json
@@ -0,0 +1 @@
+{"object":"list","data":[{"id":"gpt-4-0613","object":"model","created":1686588896,"owned_by":"openai"},{"id":"gpt-4","object":"model","created":1687882411,"owned_by":"openai"},{"id":"gpt-3.5-turbo","object":"model","created":1677610602,"owned_by":"openai"},{"id":"gpt-5.2-codex","object":"model","created":1766164985,"owned_by":"system"},{"id":"gpt-4o-mini-tts-2025-12-15","object":"model","created":1765610837,"owned_by":"system"},{"id":"gpt-realtime-mini-2025-12-15","object":"model","created":1765612007,"owned_by":"system"},{"id":"gpt-audio-mini-2025-12-15","object":"model","created":1765760008,"owned_by":"system"},{"id":"chatgpt-image-latest","object":"model","created":1765925279,"owned_by":"system"},{"id":"davinci-002","object":"model","created":1692634301,"owned_by":"system"},{"id":"babbage-002","object":"model","created":1692634615,"owned_by":"system"},{"id":"gpt-3.5-turbo-instruct","object":"model","created":1692901427,"owned_by":"system"},{"id":"gpt-3.5-turbo-instruct-0914","object":"model","created":1694122472,"owned_by":"system"},{"id":"dall-e-3","object":"model","created":1698785189,"owned_by":"system"},{"id":"dall-e-2","object":"model","created":1698798177,"owned_by":"system"},{"id":"gpt-4-1106-preview","object":"model","created":1698957206,"owned_by":"system"},{"id":"gpt-3.5-turbo-1106","object":"model","created":1698959748,"owned_by":"system"},{"id":"tts-1-hd","object":"model","created":1699046015,"owned_by":"system"},{"id":"tts-1-1106","object":"model","created":1699053241,"owned_by":"system"},{"id":"tts-1-hd-1106","object":"model","created":1699053533,"owned_by":"system"},{"id":"text-embedding-3-small","object":"model","created":1705948997,"owned_by":"system"},{"id":"text-embedding-3-large","object":"model","created":1705953180,"owned_by":"system"},{"id":"gpt-4-0125-preview","object":"model","created":1706037612,"owned_by":"system"},{"id":"gpt-4-turbo-preview","object":"model","created":1706037777,"owned_by":"system"},{"id":"gpt-3.5-turbo-0125","object":"model","created":1706048358,"owned_by":"system"},{"id":"gpt-4-turbo","object":"model","created":1712361441,"owned_by":"system"},{"id":"gpt-4-turbo-2024-04-09","object":"model","created":1712601677,"owned_by":"system"},{"id":"gpt-4o","object":"model","created":1715367049,"owned_by":"system"},{"id":"gpt-4o-2024-05-13","object":"model","created":1715368132,"owned_by":"system"},{"id":"gpt-4o-mini-2024-07-18","object":"model","created":1721172717,"owned_by":"system"},{"id":"gpt-4o-mini","object":"model","created":1721172741,"owned_by":"system"},{"id":"gpt-4o-2024-08-06","object":"model","created":1722814719,"owned_by":"system"},{"id":"chatgpt-4o-latest","object":"model","created":1723515131,"owned_by":"system"},{"id":"gpt-4o-audio-preview","object":"model","created":1727460443,"owned_by":"system"},{"id":"gpt-4o-realtime-preview","object":"model","created":1727659998,"owned_by":"system"},{"id":"omni-moderation-latest","object":"model","created":1731689265,"owned_by":"system"},{"id":"omni-moderation-2024-09-26","object":"model","created":1732734466,"owned_by":"system"},{"id":"gpt-4o-realtime-preview-2024-12-17","object":"model","created":1733945430,"owned_by":"system"},{"id":"gpt-4o-audio-preview-2024-12-17","object":"model","created":1734034239,"owned_by":"system"},{"id":"gpt-4o-mini-realtime-preview-2024-12-17","object":"model","created":1734112601,"owned_by":"system"},{"id":"gpt-4o-mini-audio-preview-2024-12-17","object":"model","created":1734115920,"owned_by":"system"},{"id":"o1-2024-12-17","object":"model","created":1734326976,"owned_by":"system"},{"id":"o1","object":"model","created":1734375816,"owned_by":"system"},{"id":"gpt-4o-mini-realtime-preview","object":"model","created":1734387380,"owned_by":"system"},{"id":"gpt-4o-mini-audio-preview","object":"model","created":1734387424,"owned_by":"system"},{"id":"o3-mini","object":"model","created":1737146383,"owned_by":"system"},{"id":"o3-mini-2025-01-31","object":"model","created":1738010200,"owned_by":"system"},{"id":"gpt-4o-2024-11-20","object":"model","created":1739331543,"owned_by":"system"},{"id":"gpt-4o-search-preview-2025-03-11","object":"model","created":1741388170,"owned_by":"system"},{"id":"gpt-4o-search-preview","object":"model","created":1741388720,"owned_by":"system"},{"id":"gpt-4o-mini-search-preview-2025-03-11","object":"model","created":1741390858,"owned_by":"system"},{"id":"gpt-4o-mini-search-preview","object":"model","created":1741391161,"owned_by":"system"},{"id":"gpt-4o-transcribe","object":"model","created":1742068463,"owned_by":"system"},{"id":"gpt-4o-mini-transcribe","object":"model","created":1742068596,"owned_by":"system"},{"id":"o1-pro-2025-03-19","object":"model","created":1742251504,"owned_by":"system"},{"id":"o1-pro","object":"model","created":1742251791,"owned_by":"system"},{"id":"gpt-4o-mini-tts","object":"model","created":1742403959,"owned_by":"system"},{"id":"o3-2025-04-16","object":"model","created":1744133301,"owned_by":"system"},{"id":"o4-mini-2025-04-16","object":"model","created":1744133506,"owned_by":"system"},{"id":"o3","object":"model","created":1744225308,"owned_by":"system"},{"id":"o4-mini","object":"model","created":1744225351,"owned_by":"system"},{"id":"gpt-4.1-2025-04-14","object":"model","created":1744315746,"owned_by":"system"},{"id":"gpt-4.1","object":"model","created":1744316542,"owned_by":"system"},{"id":"gpt-4.1-mini-2025-04-14","object":"model","created":1744317547,"owned_by":"system"},{"id":"gpt-4.1-mini","object":"model","created":1744318173,"owned_by":"system"},{"id":"gpt-4.1-nano-2025-04-14","object":"model","created":1744321025,"owned_by":"system"},{"id":"gpt-4.1-nano","object":"model","created":1744321707,"owned_by":"system"},{"id":"gpt-image-1","object":"model","created":1745517030,"owned_by":"system"},{"id":"codex-mini-latest","object":"model","created":1746673257,"owned_by":"system"},{"id":"gpt-4o-realtime-preview-2025-06-03","object":"model","created":1748907838,"owned_by":"system"},{"id":"gpt-4o-audio-preview-2025-06-03","object":"model","created":1748908498,"owned_by":"system"},{"id":"o4-mini-deep-research","object":"model","created":1749685485,"owned_by":"system"},{"id":"gpt-4o-transcribe-diarize","object":"model","created":1750798887,"owned_by":"system"},{"id":"o4-mini-deep-research-2025-06-26","object":"model","created":1750866121,"owned_by":"system"},{"id":"gpt-5-chat-latest","object":"model","created":1754073306,"owned_by":"system"},{"id":"gpt-5-2025-08-07","object":"model","created":1754075360,"owned_by":"system"},{"id":"gpt-5","object":"model","created":1754425777,"owned_by":"system"},{"id":"gpt-5-mini-2025-08-07","object":"model","created":1754425867,"owned_by":"system"},{"id":"gpt-5-mini","object":"model","created":1754425928,"owned_by":"system"},{"id":"gpt-5-nano-2025-08-07","object":"model","created":1754426303,"owned_by":"system"},{"id":"gpt-5-nano","object":"model","created":1754426384,"owned_by":"system"},{"id":"gpt-audio-2025-08-28","object":"model","created":1756256146,"owned_by":"system"},{"id":"gpt-realtime","object":"model","created":1756271701,"owned_by":"system"},{"id":"gpt-realtime-2025-08-28","object":"model","created":1756271773,"owned_by":"system"},{"id":"gpt-audio","object":"model","created":1756339249,"owned_by":"system"},{"id":"gpt-5-codex","object":"model","created":1757527818,"owned_by":"system"},{"id":"gpt-image-1-mini","object":"model","created":1758845821,"owned_by":"system"},{"id":"gpt-5-pro-2025-10-06","object":"model","created":1759469707,"owned_by":"system"},{"id":"gpt-5-pro","object":"model","created":1759469822,"owned_by":"system"},{"id":"gpt-audio-mini","object":"model","created":1759512027,"owned_by":"system"},{"id":"gpt-audio-mini-2025-10-06","object":"model","created":1759512137,"owned_by":"system"},{"id":"gpt-5-search-api","object":"model","created":1759514629,"owned_by":"system"},{"id":"gpt-realtime-mini","object":"model","created":1759517133,"owned_by":"system"},{"id":"gpt-realtime-mini-2025-10-06","object":"model","created":1759517175,"owned_by":"system"},{"id":"sora-2","object":"model","created":1759708615,"owned_by":"system"},{"id":"sora-2-pro","object":"model","created":1759708663,"owned_by":"system"},{"id":"gpt-5-search-api-2025-10-14","object":"model","created":1760043960,"owned_by":"system"},{"id":"gpt-5.1-chat-latest","object":"model","created":1762547951,"owned_by":"system"},{"id":"gpt-5.1-2025-11-13","object":"model","created":1762800353,"owned_by":"system"},{"id":"gpt-5.1","object":"model","created":1762800673,"owned_by":"system"},{"id":"gpt-5.1-codex","object":"model","created":1762988221,"owned_by":"system"},{"id":"gpt-5.1-codex-mini","object":"model","created":1763007109,"owned_by":"system"},{"id":"gpt-5.1-codex-max","object":"model","created":1763671532,"owned_by":"system"},{"id":"gpt-image-1.5","object":"model","created":1764030620,"owned_by":"system"},{"id":"gpt-5.2-2025-12-11","object":"model","created":1765313028,"owned_by":"system"},{"id":"gpt-5.2","object":"model","created":1765313051,"owned_by":"system"},{"id":"gpt-5.2-pro-2025-12-11","object":"model","created":1765343959,"owned_by":"system"},{"id":"gpt-5.2-pro","object":"model","created":1765343983,"owned_by":"system"},{"id":"gpt-5.2-chat-latest","object":"model","created":1765344352,"owned_by":"system"},{"id":"gpt-4o-mini-transcribe-2025-12-15","object":"model","created":1765610407,"owned_by":"system"},{"id":"gpt-4o-mini-transcribe-2025-03-20","object":"model","created":1765610545,"owned_by":"system"},{"id":"gpt-4o-mini-tts-2025-03-20","object":"model","created":1765610731,"owned_by":"system"},{"id":"gpt-3.5-turbo-16k","object":"model","created":1683758102,"owned_by":"openai-internal"},{"id":"tts-1","object":"model","created":1681940951,"owned_by":"openai-internal"},{"id":"whisper-1","object":"model","created":1677532384,"owned_by":"openai-internal"},{"id":"text-embedding-ada-002","object":"model","created":1671217299,"owned_by":"openai-internal"}]}
\ No newline at end of file
diff --git a/crates/goose-test-support/src/lib.rs b/crates/goose-test-support/src/lib.rs
index 4481d557d4..07cfcd7b90 100644
--- a/crates/goose-test-support/src/lib.rs
+++ b/crates/goose-test-support/src/lib.rs
@@ -2,4 +2,4 @@ pub mod mcp;
 pub mod session;
 
 pub use mcp::{McpFixture, FAKE_CODE, TEST_IMAGE_B64};
-pub use session::{ExpectedSessionId, TEST_SESSION_ID};
+pub use session::{ExpectedSessionId, TEST_MODEL, TEST_SESSION_ID};
diff --git a/crates/goose-test-support/src/session.rs b/crates/goose-test-support/src/session.rs
index a311ff5f70..30e7129020 100644
--- a/crates/goose-test-support/src/session.rs
+++ b/crates/goose-test-support/src/session.rs
@@ -1,6 +1,7 @@
 use std::sync::{Arc, Mutex};
 
 pub const TEST_SESSION_ID: &str = "test-session-id";
+pub const TEST_MODEL: &str = "gpt-5-nano";
 
 const NOT_YET_SET: &str = "session-id-not-yet-set";
 pub(crate) const SESSION_ID_HEADER: &str = "agent-session-id";
diff --git a/crates/goose/src/providers/errors.rs b/crates/goose/src/providers/errors.rs
index b72605d944..90f6d94b9d 100644
--- a/crates/goose/src/providers/errors.rs
+++ b/crates/goose/src/providers/errors.rs
@@ -2,7 +2,7 @@ use reqwest::StatusCode;
 use std::time::Duration;
 use thiserror::Error;
 
-#[derive(Error, Debug, PartialEq)]
+#[derive(Error, Debug, Clone, PartialEq)]
 pub enum ProviderError {
     #[error("Authentication error: {0}")]
     Authentication(String),
diff --git a/crates/goose/src/providers/openai.rs b/crates/goose/src/providers/openai.rs
index 63d46a5ebe..07c8e3fa7a 100644
--- a/crates/goose/src/providers/openai.rs
+++ b/crates/goose/src/providers/openai.rs
@@ -47,6 +47,7 @@ pub const OPEN_AI_KNOWN_MODELS: &[(&str, usize)] = &[
     ("gpt-3.5-turbo", 16_385),
     ("gpt-4-turbo", 128_000),
     ("o4-mini", 128_000),
+    ("gpt-5-nano", 400_000),
     ("gpt-5.1-codex", 400_000),
     ("gpt-5-codex", 400_000),
 ];