feat: add a built-in model provider named "oss"

README.md

@@ -18,6 +18,7 @@ This is the home of the **Codex CLI**, which is a coding agent from OpenAI that
 - [Quickstart](#quickstart)
   - [OpenAI API Users](#openai-api-users)
   - [OpenAI Plus/Pro Users](#openai-pluspro-users)
+  - [Using OpenAI Open Source Models](#using-open-source-models)
 - [Why Codex?](#why-codex)
 - [Security model & permissions](#security-model--permissions)
   - [Platform sandboxing details](#platform-sandboxing-details)
@@ -186,6 +187,41 @@ they'll be committed to your working directory.
 
 ---
 
+## Using Open Source Models
+
+Codex can run fully locally against an OpenAI‑compatible OSS host (like Ollama) using the `--oss` flag:
+
+- Interactive UI:
+  - codex --oss
+- Non‑interactive (programmatic) mode:
+  - echo "Refactor utils" | codex exec --oss
+
+Model selection when using `--oss`:
+
+- If you omit `-m/--model`, Codex defaults to -m gpt-oss:20b and will verify it exists locally (downloading if needed).
+- To pick a different size, pass one of:
+  - -m "gpt-oss:20b"
+  - -m "gpt-oss:120b"
+
+Point Codex at your own OSS host:
+
+- By default, `--oss` talks to http://localhost:11434/v1.
+- To use a different host, set one of these environment variables before running Codex:
+  - CODEX_OSS_BASE_URL, for example:
+    - CODEX_OSS_BASE_URL="http://my-ollama.example.com:11434/v1" codex --oss -m gpt-oss:20b
+  - or CODEX_OSS_PORT (when the host is localhost):
+    - CODEX_OSS_PORT=11434 codex --oss
+
+Advanced: you can persist this in your config instead of environment variables by overriding the built‑in `oss` provider in `~/.codex/config.toml`:
+
+```toml
+[model_providers.oss]
+name = "Open Source"
+base_url = "http://my-ollama.example.com:11434/v1"
+```
+
+---
+
 ## Why Codex?
 
 Codex CLI is built for developers who already **live in the terminal** and want

codex-rs/Cargo.lock

@@ -729,6 +729,7 @@ dependencies = [
  "codex-arg0",
  "codex-common",
  "codex-core",
+ "codex-ollama",
  "owo-colors",
  "predicates",
  "serde_json",
@@ -838,6 +839,23 @@ dependencies = [
  "wiremock",
 ]
 
+[[package]]
+name = "codex-ollama"
+version = "0.0.0"
+dependencies = [
+ "async-stream",
+ "bytes",
+ "codex-core",
+ "futures",
+ "reqwest",
+ "serde_json",
+ "tempfile",
+ "tokio",
+ "toml 0.9.4",
+ "tracing",
+ "wiremock",
+]
+
 [[package]]
 name = "codex-tui"
 version = "0.0.0"
@@ -852,6 +870,7 @@ dependencies = [
  "codex-core",
  "codex-file-search",
  "codex-login",
+ "codex-ollama",
  "color-eyre",
  "crossterm",
  "image",

codex-rs/Cargo.toml

@@ -14,6 +14,7 @@ members = [
     "mcp-client",
     "mcp-server",
     "mcp-types",
+    "ollama",
     "tui",
 ]
 resolver = "2"

codex-rs/core/src/config.rs

@@ -385,6 +385,8 @@ pub struct ConfigOverrides {
     pub codex_linux_sandbox_exe: Option<PathBuf>,
     pub base_instructions: Option<String>,
     pub include_plan_tool: Option<bool>,
+    pub default_disable_response_storage: Option<bool>,
+    pub default_show_raw_agent_reasoning: Option<bool>,
 }
 
 impl Config {
@@ -408,6 +410,8 @@ impl Config {
             codex_linux_sandbox_exe,
             base_instructions,
             include_plan_tool,
+            default_disable_response_storage,
+            default_show_raw_agent_reasoning,
         } = overrides;
 
         let config_profile = match config_profile_key.as_ref().or(cfg.profile.as_ref()) {
@@ -525,6 +529,7 @@ impl Config {
             disable_response_storage: config_profile
                 .disable_response_storage
                 .or(cfg.disable_response_storage)
+                .or(default_disable_response_storage)
                 .unwrap_or(false),
             notify: cfg.notify,
             user_instructions,
@@ -539,7 +544,10 @@ impl Config {
             codex_linux_sandbox_exe,
 
             hide_agent_reasoning: cfg.hide_agent_reasoning.unwrap_or(false),
-            show_raw_agent_reasoning: cfg.show_raw_agent_reasoning.unwrap_or(false),
+            show_raw_agent_reasoning: cfg
+                .show_raw_agent_reasoning
+                .or(default_show_raw_agent_reasoning)
+                .unwrap_or(false),
             model_reasoning_effort: config_profile
                 .model_reasoning_effort
                 .or(cfg.model_reasoning_effort)

codex-rs/core/src/lib.rs

@@ -28,6 +28,7 @@ mod mcp_connection_manager;
 mod mcp_tool_call;
 mod message_history;
 mod model_provider_info;
+pub use model_provider_info::BUILT_IN_OSS_MODEL_PROVIDER_ID;
 pub use model_provider_info::ModelProviderInfo;
 pub use model_provider_info::WireApi;
 pub use model_provider_info::built_in_model_providers;

codex-rs/core/src/model_family.rs

@@ -85,6 +85,8 @@ pub fn find_family_for_model(slug: &str) -> Option<ModelFamily> {
         )
     } else if slug.starts_with("gpt-4o") {
         simple_model_family!(slug, "gpt-4o")
+    } else if slug.starts_with("gpt-oss") {
+        simple_model_family!(slug, "gpt-oss")
     } else if slug.starts_with("gpt-3.5") {
         simple_model_family!(slug, "gpt-3.5")
     } else {

codex-rs/core/src/model_provider_info.rs

@@ -226,53 +226,93 @@ impl ModelProviderInfo {
     }
 }
 
+const DEFAULT_OLLAMA_PORT: u32 = 11434;
+
+pub const BUILT_IN_OSS_MODEL_PROVIDER_ID: &str = "oss";
+
 /// Built-in default provider list.
 pub fn built_in_model_providers() -> HashMap<String, ModelProviderInfo> {
     use ModelProviderInfo as P;
 
-    // We do not want to be in the business of adjucating which third-party
-    // providers are bundled with Codex CLI, so we only include the OpenAI
-    // provider by default. Users are encouraged to add to `model_providers`
-    // in config.toml to add their own providers.
-    [(
-        "openai",
-        P {
-            name: "OpenAI".into(),
-            // Allow users to override the default OpenAI endpoint by
-            // exporting `OPENAI_BASE_URL`. This is useful when pointing
-            // Codex at a proxy, mock server, or Azure-style deployment
-            // without requiring a full TOML override for the built-in
-            // OpenAI provider.
-            base_url: std::env::var("OPENAI_BASE_URL")
+    // These CODEX_OSS_ environment variables are experimental: we may
+    // switch to reading values from config.toml instead.
+    let codex_oss_base_url = match std::env::var("CODEX_OSS_BASE_URL")
+        .ok()
+        .filter(|v| !v.trim().is_empty())
+    {
+        Some(url) => url,
+        None => format!(
+            "http://localhost:{port}/v1",
+            port = std::env::var("CODEX_OSS_PORT")
                 .ok()
-                .filter(|v| !v.trim().is_empty()),
-            env_key: None,
-            env_key_instructions: None,
-            wire_api: WireApi::Responses,
-            query_params: None,
-            http_headers: Some(
-                [("version".to_string(), env!("CARGO_PKG_VERSION").to_string())]
+                .filter(|v| !v.trim().is_empty())
+                .and_then(|v| v.parse::<u32>().ok())
+                .unwrap_or(DEFAULT_OLLAMA_PORT)
+        ),
+    };
+
+    // We do not want to be in the business of adjucating which third-party
+    // providers are bundled with Codex CLI, so we only include the OpenAI and
+    // open source ("oss") providers by default. Users are encouraged to add to
+    // `model_providers` in config.toml to add their own providers.
+    [
+        (
+            "openai",
+            P {
+                name: "OpenAI".into(),
+                // Allow users to override the default OpenAI endpoint by
+                // exporting `OPENAI_BASE_URL`. This is useful when pointing
+                // Codex at a proxy, mock server, or Azure-style deployment
+                // without requiring a full TOML override for the built-in
+                // OpenAI provider.
+                base_url: std::env::var("OPENAI_BASE_URL")
+                    .ok()
+                    .filter(|v| !v.trim().is_empty()),
+                env_key: None,
+                env_key_instructions: None,
+                wire_api: WireApi::Responses,
+                query_params: None,
+                http_headers: Some(
+                    [("version".to_string(), env!("CARGO_PKG_VERSION").to_string())]
+                        .into_iter()
+                        .collect(),
+                ),
+                env_http_headers: Some(
+                    [
+                        (
+                            "OpenAI-Organization".to_string(),
+                            "OPENAI_ORGANIZATION".to_string(),
+                        ),
+                        ("OpenAI-Project".to_string(), "OPENAI_PROJECT".to_string()),
+                    ]
                     .into_iter()
                     .collect(),
-            ),
-            env_http_headers: Some(
-                [
-                    (
-                        "OpenAI-Organization".to_string(),
-                        "OPENAI_ORGANIZATION".to_string(),
-                    ),
-                    ("OpenAI-Project".to_string(), "OPENAI_PROJECT".to_string()),
-                ]
-                .into_iter()
-                .collect(),
-            ),
-            // Use global defaults for retry/timeout unless overridden in config.toml.
-            request_max_retries: None,
-            stream_max_retries: None,
-            stream_idle_timeout_ms: None,
-            requires_auth: true,
-        },
-    )]
+                ),
+                // Use global defaults for retry/timeout unless overridden in config.toml.
+                request_max_retries: None,
+                stream_max_retries: None,
+                stream_idle_timeout_ms: None,
+                requires_auth: true,
+            },
+        ),
+        (
+            BUILT_IN_OSS_MODEL_PROVIDER_ID,
+            P {
+                name: "Open Source".into(),
+                base_url: Some(codex_oss_base_url),
+                env_key: None,
+                env_key_instructions: None,
+                wire_api: WireApi::Chat,
+                query_params: None,
+                http_headers: None,
+                env_http_headers: None,
+                request_max_retries: None,
+                stream_max_retries: None,
+                stream_idle_timeout_ms: None,
+                requires_auth: false,
+            },
+        ),
+    ]
     .into_iter()
     .map(|(k, v)| (k.to_string(), v))
     .collect()

codex-rs/exec/Cargo.toml

@@ -25,6 +25,7 @@ codex-common = { path = "../common", features = [
     "sandbox_summary",
 ] }
 codex-core = { path = "../core" }
+codex-ollama = { path = "../ollama" }
 owo-colors = "4.2.0"
 serde_json = "1"
 shlex = "1.3.0"

codex-rs/exec/src/cli.rs

@@ -14,6 +14,9 @@ pub struct Cli {
     #[arg(long, short = 'm')]
     pub model: Option<String>,
 
+    #[arg(long = "oss", default_value_t = false)]
+    pub oss: bool,
+
     /// Select the sandbox policy to use when executing model-generated shell
     /// commands.
     #[arg(long = "sandbox", short = 's')]

codex-rs/exec/src/lib.rs

@@ -9,6 +9,7 @@ use std::path::PathBuf;
 use std::sync::Arc;
 
 pub use cli::Cli;
+use codex_core::BUILT_IN_OSS_MODEL_PROVIDER_ID;
 use codex_core::codex_wrapper::CodexConversation;
 use codex_core::codex_wrapper::{self};
 use codex_core::config::Config;
@@ -35,6 +36,7 @@ pub async fn run_main(cli: Cli, codex_linux_sandbox_exe: Option<PathBuf>) -> any
     let Cli {
         images,
         model,
+        oss,
         config_profile,
         full_auto,
         dangerously_bypass_approvals_and_sandbox,
@@ -114,6 +116,24 @@ pub async fn run_main(cli: Cli, codex_linux_sandbox_exe: Option<PathBuf>) -> any
         sandbox_mode_cli_arg.map(Into::<SandboxMode>::into)
     };
 
+    // When using `--oss`, let the bootstrapper pick the model (defaulting to
+    // gpt-oss:20b) and ensure it is present locally. Also, force the built‑in
+    // `oss` model provider.
+    let model_provider_override = if oss {
+        Some(BUILT_IN_OSS_MODEL_PROVIDER_ID.to_owned())
+    } else {
+        None
+    };
+    let model = if oss {
+        Some(
+            codex_ollama::ensure_oss_ready(model.clone())
+                .await
+                .map_err(|e| anyhow::anyhow!("OSS setup failed: {e}"))?,
+        )
+    } else {
+        model
+    };
+
     // Load configuration and determine approval policy
     let overrides = ConfigOverrides {
         model,
@@ -123,10 +143,12 @@ pub async fn run_main(cli: Cli, codex_linux_sandbox_exe: Option<PathBuf>) -> any
         approval_policy: Some(AskForApproval::Never),
         sandbox_mode,
         cwd: cwd.map(|p| p.canonicalize().unwrap_or(p)),
-        model_provider: None,
+        model_provider: model_provider_override,
         codex_linux_sandbox_exe,
         base_instructions: None,
         include_plan_tool: None,
+        default_disable_response_storage: oss.then_some(true),
+        default_show_raw_agent_reasoning: oss.then_some(true),
     };
     // Parse `-c` overrides.
     let cli_kv_overrides = match config_overrides.parse_overrides() {

codex-rs/mcp-server/src/codex_tool_config.rs

@@ -158,6 +158,8 @@ impl CodexToolCallParam {
             codex_linux_sandbox_exe,
             base_instructions,
             include_plan_tool,
+            default_disable_response_storage: None,
+            default_show_raw_agent_reasoning: None,
         };
 
         let cli_overrides = cli_overrides

codex-rs/mcp-server/src/tool_handlers/create_conversation.rs

@@ -59,6 +59,8 @@ pub(crate) async fn handle_create_conversation(
         codex_linux_sandbox_exe: None,
         base_instructions,
         include_plan_tool: None,
+        default_disable_response_storage: None,
+        default_show_raw_agent_reasoning: None,
     };
 
     let cfg: CodexConfig = match CodexConfig::load_with_cli_overrides(cli_overrides, overrides) {

codex-rs/ollama/Cargo.toml

@@ -0,0 +1,32 @@
+[package]
+edition = "2024"
+name = "codex-ollama"
+version = { workspace = true }
+
+[lib]
+name = "codex_ollama"
+path = "src/lib.rs"
+
+[lints]
+workspace = true
+
+[dependencies]
+async-stream = "0.3"
+bytes = "1.10.1"
+codex-core = { path = "../core" }
+futures = "0.3"
+reqwest = { version = "0.12", features = ["json", "stream"] }
+serde_json = "1"
+tokio = { version = "1", features = [
+    "io-std",
+    "macros",
+    "process",
+    "rt-multi-thread",
+    "signal",
+] }
+toml = "0.9.2"
+tracing = { version = "0.1.41", features = ["log"] }
+wiremock = "0.6"
+
+[dev-dependencies]
+tempfile = "3"

codex-rs/ollama/src/client.rs

@@ -0,0 +1,366 @@
+use bytes::BytesMut;
+use futures::StreamExt;
+use futures::stream::BoxStream;
+use serde_json::Value as JsonValue;
+use std::collections::VecDeque;
+use std::io;
+
+use codex_core::WireApi;
+
+use crate::parser::pull_events_from_value;
+use crate::pull::PullEvent;
+use crate::pull::PullProgressReporter;
+use crate::url::base_url_to_host_root;
+use crate::url::is_openai_compatible_base_url;
+
+/// Client for interacting with a local Ollama instance.
+pub struct OllamaClient {
+    client: reqwest::Client,
+    host_root: String,
+    uses_openai_compat: bool,
+}
+
+impl OllamaClient {
+    pub fn from_oss_provider() -> Self {
+        #![allow(clippy::expect_used)]
+        // Use the built-in OSS provider's base URL.
+        let built_in_model_providers = codex_core::built_in_model_providers();
+        let provider = built_in_model_providers
+            .get(codex_core::BUILT_IN_OSS_MODEL_PROVIDER_ID)
+            .expect("oss provider must exist");
+        let base_url = provider
+            .base_url
+            .as_ref()
+            .expect("oss provider must have a base_url");
+        Self::from_provider(base_url, provider.wire_api)
+    }
+
+    /// Construct a client for the built‑in open‑source ("oss") model provider
+    /// and verify that a local Ollama server is reachable. If no server is
+    /// detected, returns an error with helpful installation/run instructions.
+    pub async fn try_from_oss_provider() -> io::Result<Self> {
+        let client = Self::from_oss_provider();
+        if client.probe_server().await? {
+            Ok(client)
+        } else {
+            Err(io::Error::other(
+                "No running Ollama server detected. Start it with: `ollama serve` (after installing). Install instructions: https://github.com/ollama/ollama?tab=readme-ov-file#ollama",
+            ))
+        }
+    }
+
+    /// Build a client from a provider definition. Falls back to the default
+    /// local URL if no base_url is configured.
+    fn from_provider(base_url: &str, wire_api: WireApi) -> Self {
+        let uses_openai_compat = is_openai_compatible_base_url(base_url)
+            || matches!(wire_api, WireApi::Chat) && is_openai_compatible_base_url(base_url);
+        let host_root = base_url_to_host_root(base_url);
+        let client = reqwest::Client::builder()
+            .connect_timeout(std::time::Duration::from_secs(5))
+            .build()
+            .unwrap_or_else(|_| reqwest::Client::new());
+        Self {
+            client,
+            host_root,
+            uses_openai_compat,
+        }
+    }
+
+    /// Low-level constructor given a raw host root, e.g. "http://localhost:11434".
+    #[cfg(test)]
+    fn from_host_root(host_root: impl Into<String>) -> Self {
+        let client = reqwest::Client::builder()
+            .connect_timeout(std::time::Duration::from_secs(5))
+            .build()
+            .unwrap_or_else(|_| reqwest::Client::new());
+        Self {
+            client,
+            host_root: host_root.into(),
+            uses_openai_compat: false,
+        }
+    }
+
+    /// Probe whether the server is reachable by hitting the appropriate health endpoint.
+    pub async fn probe_server(&self) -> io::Result<bool> {
+        let url = if self.uses_openai_compat {
+            format!("{}/v1/models", self.host_root.trim_end_matches('/'))
+        } else {
+            format!("{}/api/tags", self.host_root.trim_end_matches('/'))
+        };
+        let resp = self.client.get(url).send().await;
+        Ok(matches!(resp, Ok(r) if r.status().is_success()))
+    }
+
+    /// Return the list of model names known to the local Ollama instance.
+    pub async fn fetch_models(&self) -> io::Result<Vec<String>> {
+        let tags_url = format!("{}/api/tags", self.host_root.trim_end_matches('/'));
+        let resp = self
+            .client
+            .get(tags_url)
+            .send()
+            .await
+            .map_err(io::Error::other)?;
+        if !resp.status().is_success() {
+            return Ok(Vec::new());
+        }
+        let val = resp.json::<JsonValue>().await.map_err(io::Error::other)?;
+        let names = val
+            .get("models")
+            .and_then(|m| m.as_array())
+            .map(|arr| {
+                arr.iter()
+                    .filter_map(|v| v.get("name").and_then(|n| n.as_str()))
+                    .map(|s| s.to_string())
+                    .collect::<Vec<_>>()
+            })
+            .unwrap_or_default();
+        Ok(names)
+    }
+
+    /// Start a model pull and emit streaming events. The returned stream ends when
+    /// a Success event is observed or the server closes the connection.
+    pub async fn pull_model_stream(
+        &self,
+        model: &str,
+    ) -> io::Result<BoxStream<'static, PullEvent>> {
+        let url = format!("{}/api/pull", self.host_root.trim_end_matches('/'));
+        let resp = self
+            .client
+            .post(url)
+            .json(&serde_json::json!({"model": model, "stream": true}))
+            .send()
+            .await
+            .map_err(io::Error::other)?;
+        if !resp.status().is_success() {
+            return Err(io::Error::other(format!(
+                "failed to start pull: HTTP {}",
+                resp.status()
+            )));
+        }
+
+        let mut stream = resp.bytes_stream();
+        let mut buf = BytesMut::new();
+        let _pending: VecDeque<PullEvent> = VecDeque::new();
+
+        // Using an async stream adaptor backed by unfold-like manual loop.
+        let s = async_stream::stream! {
+            while let Some(chunk) = stream.next().await {
+                match chunk {
+                    Ok(bytes) => {
+                        buf.extend_from_slice(&bytes);
+                        while let Some(pos) = buf.iter().position(|b| *b == b'\n') {
+                            let line = buf.split_to(pos + 1);
+                            if let Ok(text) = std::str::from_utf8(&line) {
+                                let text = text.trim();
+                                if text.is_empty() { continue; }
+                                if let Ok(value) = serde_json::from_str::<JsonValue>(text) {
+                                    for ev in pull_events_from_value(&value) { yield ev; }
+                                    if let Some(err_msg) = value.get("error").and_then(|e| e.as_str()) {
+                                        yield PullEvent::Error(err_msg.to_string());
+                                        return;
+                                    }
+                                    if let Some(status) = value.get("status").and_then(|s| s.as_str()) {
+                                        if status == "success" { yield PullEvent::Success; return; }
+                                    }
+                                }
+                            }
+                        }
+                    }
+                    Err(_) => {
+                        // Connection error: end the stream.
+                        return;
+                    }
+                }
+            }
+        };
+
+        Ok(Box::pin(s))
+    }
+
+    /// High-level helper to pull a model and drive a progress reporter.
+    pub async fn pull_with_reporter(
+        &self,
+        model: &str,
+        reporter: &mut dyn PullProgressReporter,
+    ) -> io::Result<()> {
+        reporter.on_event(&PullEvent::Status(format!("Pulling model {model}...")))?;
+        let mut stream = self.pull_model_stream(model).await?;
+        while let Some(event) = stream.next().await {
+            reporter.on_event(&event)?;
+            match event {
+                PullEvent::Success => {
+                    return Ok(());
+                }
+                PullEvent::Error(err) => {
+                    // Emperically, ollama returns a 200 OK response even when
+                    // the output stream includes an error message. Verify with:
+                    //
+                    // `curl -i http://localhost:11434/api/pull -d '{ "model": "foobarbaz" }'`
+                    //
+                    // As such, we have to check the event stream, not the
+                    // HTTP response status, to determine whether to return Err.
+                    return Err(io::Error::other(format!("Pull failed: {err}")));
+                }
+                PullEvent::ChunkProgress { .. } | PullEvent::Status(_) => {
+                    continue;
+                }
+            }
+        }
+        Err(io::Error::other(
+            "Pull stream ended unexpectedly without success.",
+        ))
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    #![allow(clippy::expect_used, clippy::unwrap_used)]
+    use super::*;
+
+    /// Simple RAII guard to set an environment variable for the duration of a test
+    /// and restore the previous value (or remove it) on drop to avoid cross-test
+    /// interference.
+    struct EnvVarGuard {
+        key: String,
+        prev: Option<String>,
+    }
+    impl EnvVarGuard {
+        fn set(key: &str, value: String) -> Self {
+            let prev = std::env::var(key).ok();
+            // set_var is safe but we mirror existing tests that use an unsafe block
+            // to silence edition lints around global mutation during tests.
+            unsafe { std::env::set_var(key, value) };
+            Self {
+                key: key.to_string(),
+                prev,
+            }
+        }
+    }
+    impl Drop for EnvVarGuard {
+        fn drop(&mut self) {
+            match &self.prev {
+                Some(v) => unsafe { std::env::set_var(&self.key, v) },
+                None => unsafe { std::env::remove_var(&self.key) },
+            }
+        }
+    }
+
+    // Happy-path tests using a mock HTTP server; skip if sandbox network is disabled.
+    #[tokio::test]
+    async fn test_fetch_models_happy_path() {
+        if std::env::var(codex_core::spawn::CODEX_SANDBOX_NETWORK_DISABLED_ENV_VAR).is_ok() {
+            tracing::info!(
+                "{} is set; skipping test_fetch_models_happy_path",
+                codex_core::spawn::CODEX_SANDBOX_NETWORK_DISABLED_ENV_VAR
+            );
+            return;
+        }
+
+        let server = wiremock::MockServer::start().await;
+        wiremock::Mock::given(wiremock::matchers::method("GET"))
+            .and(wiremock::matchers::path("/api/tags"))
+            .respond_with(
+                wiremock::ResponseTemplate::new(200).set_body_raw(
+                    serde_json::json!({
+                        "models": [ {"name": "llama3.2:3b"}, {"name":"mistral"} ]
+                    })
+                    .to_string(),
+                    "application/json",
+                ),
+            )
+            .mount(&server)
+            .await;
+
+        let client = OllamaClient::from_host_root(server.uri());
+        let models = client.fetch_models().await.expect("fetch models");
+        assert!(models.contains(&"llama3.2:3b".to_string()));
+        assert!(models.contains(&"mistral".to_string()));
+    }
+
+    #[tokio::test]
+    async fn test_probe_server_happy_path_openai_compat_and_native() {
+        if std::env::var(codex_core::spawn::CODEX_SANDBOX_NETWORK_DISABLED_ENV_VAR).is_ok() {
+            tracing::info!(
+                "{} set; skipping test_probe_server_happy_path_openai_compat_and_native",
+                codex_core::spawn::CODEX_SANDBOX_NETWORK_DISABLED_ENV_VAR
+            );
+            return;
+        }
+
+        let server = wiremock::MockServer::start().await;
+
+        // Native endpoint
+        wiremock::Mock::given(wiremock::matchers::method("GET"))
+            .and(wiremock::matchers::path("/api/tags"))
+            .respond_with(wiremock::ResponseTemplate::new(200))
+            .mount(&server)
+            .await;
+        let native = OllamaClient::from_host_root(server.uri());
+        assert!(native.probe_server().await.expect("probe native"));
+
+        // OpenAI compatibility endpoint
+        wiremock::Mock::given(wiremock::matchers::method("GET"))
+            .and(wiremock::matchers::path("/v1/models"))
+            .respond_with(wiremock::ResponseTemplate::new(200))
+            .mount(&server)
+            .await;
+        // Ensure the built-in OSS provider points at our mock server for this test
+        // to avoid depending on any globally configured environment from other tests.
+        let _guard = EnvVarGuard::set("CODEX_OSS_BASE_URL", format!("{}/v1", server.uri()));
+        let ollama_client = OllamaClient::from_oss_provider();
+        assert!(ollama_client.probe_server().await.expect("probe compat"));
+    }
+
+    #[tokio::test]
+    async fn test_try_from_oss_provider_ok_when_server_running() {
+        if std::env::var(codex_core::spawn::CODEX_SANDBOX_NETWORK_DISABLED_ENV_VAR).is_ok() {
+            tracing::info!(
+                "{} set; skipping test_try_from_oss_provider_ok_when_server_running",
+                codex_core::spawn::CODEX_SANDBOX_NETWORK_DISABLED_ENV_VAR
+            );
+            return;
+        }
+
+        let server = wiremock::MockServer::start().await;
+        // Configure built‑in `oss` provider to point at this mock server.
+        // set_var is unsafe on Rust 2024 edition; use unsafe block in tests.
+        let _guard = EnvVarGuard::set("CODEX_OSS_BASE_URL", format!("{}/v1", server.uri()));
+
+        // OpenAI‑compat models endpoint responds OK.
+        wiremock::Mock::given(wiremock::matchers::method("GET"))
+            .and(wiremock::matchers::path("/v1/models"))
+            .respond_with(wiremock::ResponseTemplate::new(200))
+            .mount(&server)
+            .await;
+
+        let _client = OllamaClient::try_from_oss_provider()
+            .await
+            .expect("client should be created when probe succeeds");
+    }
+
+    #[tokio::test]
+    async fn test_try_from_oss_provider_err_when_server_missing() {
+        if std::env::var(codex_core::spawn::CODEX_SANDBOX_NETWORK_DISABLED_ENV_VAR).is_ok() {
+            tracing::info!(
+                "{} set; skipping test_try_from_oss_provider_err_when_server_missing",
+                codex_core::spawn::CODEX_SANDBOX_NETWORK_DISABLED_ENV_VAR
+            );
+            return;
+        }
+
+        let server = wiremock::MockServer::start().await;
+        // Point oss provider at our mock server but do NOT set up a handler
+        // for /v1/models so the request returns a non‑success status.
+        unsafe { std::env::set_var("CODEX_OSS_BASE_URL", format!("{}/v1", server.uri())) };
+
+        let err = OllamaClient::try_from_oss_provider()
+            .await
+            .err()
+            .expect("expected error");
+        let msg = err.to_string();
+        assert!(
+            msg.contains("No running Ollama server detected."),
+            "msg = {msg}"
+        );
+    }
+}

codex-rs/ollama/src/lib.rs

@@ -0,0 +1,52 @@
+mod client;
+mod parser;
+mod pull;
+mod url;
+
+pub use client::OllamaClient;
+pub use pull::CliProgressReporter;
+pub use pull::PullEvent;
+pub use pull::PullProgressReporter;
+pub use pull::TuiProgressReporter;
+
+/// Default OSS model to use when `--oss` is passed without an explicit `-m`.
+pub const DEFAULT_OSS_MODEL: &str = "gpt-oss:20b";
+
+/// Prepare the local OSS environment when `--oss` is selected.
+///
+/// - Ensures a local Ollama server is reachable.
+/// - Selects the final model name (CLI override or default).
+/// - Checks if the model exists locally and pulls it if missing.
+///
+/// Returns the final model name that should be used by the caller.
+pub async fn ensure_oss_ready(cli_model: Option<String>) -> std::io::Result<String> {
+    // Only download when the requested model is the default OSS model (or when -m is not provided).
+    let should_download = cli_model
+        .as_deref()
+        .map(|name| name == DEFAULT_OSS_MODEL)
+        .unwrap_or(true);
+    let model = cli_model.unwrap_or_else(|| DEFAULT_OSS_MODEL.to_string());
+
+    // Verify local Ollama is reachable.
+    let ollama_client = crate::OllamaClient::try_from_oss_provider().await?;
+
+    if should_download {
+        // If the model is not present locally, pull it.
+        match ollama_client.fetch_models().await {
+            Ok(models) => {
+                if !models.iter().any(|m| m == &model) {
+                    let mut reporter = crate::CliProgressReporter::new();
+                    ollama_client
+                        .pull_with_reporter(&model, &mut reporter)
+                        .await?;
+                }
+            }
+            Err(err) => {
+                // Not fatal; higher layers may still proceed and surface errors later.
+                tracing::warn!("Failed to query local models from Ollama: {}.", err);
+            }
+        }
+    }
+
+    Ok(model)
+}

codex-rs/ollama/src/parser.rs

@@ -0,0 +1,82 @@
+use serde_json::Value as JsonValue;
+
+use crate::pull::PullEvent;
+
+// Convert a single JSON object representing a pull update into one or more events.
+pub(crate) fn pull_events_from_value(value: &JsonValue) -> Vec<PullEvent> {
+    let mut events = Vec::new();
+    if let Some(status) = value.get("status").and_then(|s| s.as_str()) {
+        events.push(PullEvent::Status(status.to_string()));
+        if status == "success" {
+            events.push(PullEvent::Success);
+        }
+    }
+    let digest = value
+        .get("digest")
+        .and_then(|d| d.as_str())
+        .unwrap_or("")
+        .to_string();
+    let total = value.get("total").and_then(|t| t.as_u64());
+    let completed = value.get("completed").and_then(|t| t.as_u64());
+    if total.is_some() || completed.is_some() {
+        events.push(PullEvent::ChunkProgress {
+            digest,
+            total,
+            completed,
+        });
+    }
+    events
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_pull_events_decoder_status_and_success() {
+        let v: JsonValue = serde_json::json!({"status":"verifying"});
+        let events = pull_events_from_value(&v);
+        assert!(matches!(events.as_slice(), [PullEvent::Status(s)] if s == "verifying"));
+
+        let v2: JsonValue = serde_json::json!({"status":"success"});
+        let events2 = pull_events_from_value(&v2);
+        assert_eq!(events2.len(), 2);
+        assert!(matches!(events2[0], PullEvent::Status(ref s) if s == "success"));
+        assert!(matches!(events2[1], PullEvent::Success));
+    }
+
+    #[test]
+    fn test_pull_events_decoder_progress() {
+        let v: JsonValue = serde_json::json!({"digest":"sha256:abc","total":100});
+        let events = pull_events_from_value(&v);
+        assert_eq!(events.len(), 1);
+        match &events[0] {
+            PullEvent::ChunkProgress {
+                digest,
+                total,
+                completed,
+            } => {
+                assert_eq!(digest, "sha256:abc");
+                assert_eq!(*total, Some(100));
+                assert_eq!(*completed, None);
+            }
+            _ => panic!("expected ChunkProgress"),
+        }
+
+        let v2: JsonValue = serde_json::json!({"digest":"sha256:def","completed":42});
+        let events2 = pull_events_from_value(&v2);
+        assert_eq!(events2.len(), 1);
+        match &events2[0] {
+            PullEvent::ChunkProgress {
+                digest,
+                total,
+                completed,
+            } => {
+                assert_eq!(digest, "sha256:def");
+                assert_eq!(*total, None);
+                assert_eq!(*completed, Some(42));
+            }
+            _ => panic!("expected ChunkProgress"),
+        }
+    }
+}

codex-rs/ollama/src/pull.rs

@@ -0,0 +1,147 @@
+use std::collections::HashMap;
+use std::io;
+use std::io::Write;
+
+/// Events emitted while pulling a model from Ollama.
+#[derive(Debug, Clone)]
+pub enum PullEvent {
+    /// A human-readable status message (e.g., "verifying", "writing").
+    Status(String),
+    /// Byte-level progress update for a specific layer digest.
+    ChunkProgress {
+        digest: String,
+        total: Option<u64>,
+        completed: Option<u64>,
+    },
+    /// The pull finished successfully.
+    Success,
+
+    /// Error event with a message.
+    Error(String),
+}
+
+/// A simple observer for pull progress events. Implementations decide how to
+/// render progress (CLI, TUI, logs, ...).
+pub trait PullProgressReporter {
+    fn on_event(&mut self, event: &PullEvent) -> io::Result<()>;
+}
+
+/// A minimal CLI reporter that writes inline progress to stderr.
+pub struct CliProgressReporter {
+    printed_header: bool,
+    last_line_len: usize,
+    last_completed_sum: u64,
+    last_instant: std::time::Instant,
+    totals_by_digest: HashMap<String, (u64, u64)>,
+}
+
+impl Default for CliProgressReporter {
+    fn default() -> Self {
+        Self::new()
+    }
+}
+
+impl CliProgressReporter {
+    pub fn new() -> Self {
+        Self {
+            printed_header: false,
+            last_line_len: 0,
+            last_completed_sum: 0,
+            last_instant: std::time::Instant::now(),
+            totals_by_digest: HashMap::new(),
+        }
+    }
+}
+
+impl PullProgressReporter for CliProgressReporter {
+    fn on_event(&mut self, event: &PullEvent) -> io::Result<()> {
+        let mut out = std::io::stderr();
+        match event {
+            PullEvent::Status(status) => {
+                // Avoid noisy manifest messages; otherwise show status inline.
+                if status.eq_ignore_ascii_case("pulling manifest") {
+                    return Ok(());
+                }
+                let pad = self.last_line_len.saturating_sub(status.len());
+                let line = format!("\r{status}{}", " ".repeat(pad));
+                self.last_line_len = status.len();
+                out.write_all(line.as_bytes())?;
+                out.flush()
+            }
+            PullEvent::ChunkProgress {
+                digest,
+                total,
+                completed,
+            } => {
+                if let Some(t) = *total {
+                    self.totals_by_digest
+                        .entry(digest.clone())
+                        .or_insert((0, 0))
+                        .0 = t;
+                }
+                if let Some(c) = *completed {
+                    self.totals_by_digest
+                        .entry(digest.clone())
+                        .or_insert((0, 0))
+                        .1 = c;
+                }
+
+                let (sum_total, sum_completed) = self
+                    .totals_by_digest
+                    .values()
+                    .fold((0u64, 0u64), |acc, (t, c)| (acc.0 + *t, acc.1 + *c));
+                if sum_total > 0 {
+                    if !self.printed_header {
+                        let gb = (sum_total as f64) / (1024.0 * 1024.0 * 1024.0);
+                        let header = format!("Downloading model: total {gb:.2} GB\n");
+                        out.write_all(b"\r\x1b[2K")?;
+                        out.write_all(header.as_bytes())?;
+                        self.printed_header = true;
+                    }
+                    let now = std::time::Instant::now();
+                    let dt = now
+                        .duration_since(self.last_instant)
+                        .as_secs_f64()
+                        .max(0.001);
+                    let dbytes = sum_completed.saturating_sub(self.last_completed_sum) as f64;
+                    let speed_mb_s = dbytes / (1024.0 * 1024.0) / dt;
+                    self.last_completed_sum = sum_completed;
+                    self.last_instant = now;
+
+                    let done_gb = (sum_completed as f64) / (1024.0 * 1024.0 * 1024.0);
+                    let total_gb = (sum_total as f64) / (1024.0 * 1024.0 * 1024.0);
+                    let pct = (sum_completed as f64) * 100.0 / (sum_total as f64);
+                    let text =
+                        format!("{done_gb:.2}/{total_gb:.2} GB ({pct:.1}%) {speed_mb_s:.1} MB/s");
+                    let pad = self.last_line_len.saturating_sub(text.len());
+                    let line = format!("\r{text}{}", " ".repeat(pad));
+                    self.last_line_len = text.len();
+                    out.write_all(line.as_bytes())?;
+                    out.flush()
+                } else {
+                    Ok(())
+                }
+            }
+            PullEvent::Error(_) => {
+                // This will be handled by the caller, so we don't do anything
+                // here or the error will be printed twice.
+                Ok(())
+            }
+            PullEvent::Success => {
+                out.write_all(b"\n")?;
+                out.flush()
+            }
+        }
+    }
+}
+
+/// For now the TUI reporter delegates to the CLI reporter. This keeps UI and
+/// CLI behavior aligned until a dedicated TUI integration is implemented.
+#[derive(Default)]
+pub struct TuiProgressReporter(CliProgressReporter);
+
+impl PullProgressReporter for TuiProgressReporter {
+    fn on_event(&mut self, event: &PullEvent) -> io::Result<()> {
+        self.0.on_event(event)
+    }
+}

codex-rs/ollama/src/url.rs

@@ -0,0 +1,39 @@
+/// Identify whether a base_url points at an OpenAI-compatible root (".../v1").
+pub(crate) fn is_openai_compatible_base_url(base_url: &str) -> bool {
+    base_url.trim_end_matches('/').ends_with("/v1")
+}
+
+/// Convert a provider base_url into the native Ollama host root.
+/// For example, "http://localhost:11434/v1" -> "http://localhost:11434".
+pub fn base_url_to_host_root(base_url: &str) -> String {
+    let trimmed = base_url.trim_end_matches('/');
+    if trimmed.ends_with("/v1") {
+        trimmed
+            .trim_end_matches("/v1")
+            .trim_end_matches('/')
+            .to_string()
+    } else {
+        trimmed.to_string()
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_base_url_to_host_root() {
+        assert_eq!(
+            base_url_to_host_root("http://localhost:11434/v1"),
+            "http://localhost:11434"
+        );
+        assert_eq!(
+            base_url_to_host_root("http://localhost:11434"),
+            "http://localhost:11434"
+        );
+        assert_eq!(
+            base_url_to_host_root("http://localhost:11434/"),
+            "http://localhost:11434"
+        );
+    }
+}

codex-rs/tui/Cargo.toml

@@ -33,6 +33,7 @@ codex-common = { path = "../common", features = [
 codex-core = { path = "../core" }
 codex-file-search = { path = "../file-search" }
 codex-login = { path = "../login" }
+codex-ollama = { path = "../ollama" }
 color-eyre = "0.6.3"
 crossterm = { version = "0.28.1", features = ["bracketed-paste"] }
 image = { version = "^0.25.6", default-features = false, features = ["jpeg"] }

codex-rs/tui/src/cli.rs

@@ -17,6 +17,12 @@ pub struct Cli {
     #[arg(long, short = 'm')]
     pub model: Option<String>,
 
+    /// Convenience flag to select the local open source model provider.
+    /// Equivalent to -c model_provider=oss; verifies a local Ollama server is
+    /// running.
+    #[arg(long = "oss", default_value_t = false)]
+    pub oss: bool,
+
     /// Configuration profile from config.toml to specify default options.
     #[arg(long = "profile", short = 'p')]
     pub config_profile: Option<String>,

codex-rs/tui/src/lib.rs

@@ -3,6 +3,7 @@
 // alternate‑screen mode starts; that file opts‑out locally via `allow`.
 #![deny(clippy::print_stdout, clippy::print_stderr)]
 use app::App;
+use codex_core::BUILT_IN_OSS_MODEL_PROVIDER_ID;
 use codex_core::config::Config;
 use codex_core::config::ConfigOverrides;
 use codex_core::config_types::SandboxMode;
@@ -70,18 +71,35 @@ pub async fn run_main(
         )
     };
 
+    let model_provider_override = if cli.oss {
+        Some(BUILT_IN_OSS_MODEL_PROVIDER_ID.to_owned())
+    } else {
+        None
+    };
     let config = {
         // Load configuration and support CLI overrides.
         let overrides = ConfigOverrides {
-            model: cli.model.clone(),
+            // When using `--oss`, let the bootstrapper pick the model
+            // (defaulting to gpt-oss:20b) and ensure it is present locally.
+            model: if cli.oss {
+                Some(
+                    codex_ollama::ensure_oss_ready(cli.model.clone())
+                        .await
+                        .map_err(|e| std::io::Error::other(format!("OSS setup failed: {e}")))?,
+                )
+            } else {
+                cli.model.clone()
+            },
             approval_policy,
             sandbox_mode,
             cwd: cli.cwd.clone().map(|p| p.canonicalize().unwrap_or(p)),
-            model_provider: None,
+            model_provider: model_provider_override,
             config_profile: cli.config_profile.clone(),
             codex_linux_sandbox_exe,
             base_instructions: None,
             include_plan_tool: Some(true),
+            default_disable_response_storage: cli.oss.then_some(true),
+            default_show_raw_agent_reasoning: cli.oss.then_some(true),
         };
         // Parse `-c` overrides from the CLI.
         let cli_kv_overrides = match cli.config_overrides.parse_overrides() {