diff --git a/rust/crates/api/src/providers/openai_compat.rs b/rust/crates/api/src/providers/openai_compat.rs
index b3800d6a..f66710ab 100644
--- a/rust/crates/api/src/providers/openai_compat.rs
+++ b/rust/crates/api/src/providers/openai_compat.rs
@@ -1,3 +1,4 @@
+use std::borrow::Cow;
 use std::collections::{BTreeMap, VecDeque};
 use std::sync::atomic::{AtomicU64, Ordering};
 use std::time::{Duration, SystemTime, UNIX_EPOCH};
@@ -267,14 +268,18 @@ impl OpenAiCompatClient {
         request: &MessageRequest,
     ) -> Result<reqwest::Response, ApiError> {
         // Pre-flight check: verify request body size against provider limits
-        check_request_body_size(request, self.config())?;
+        check_request_body_size_for_base_url(request, self.config(), &self.base_url)?;
 
         let request_url = chat_completions_endpoint(&self.base_url);
         self.http
             .post(&request_url)
             .header("content-type", "application/json")
             .bearer_auth(&self.api_key)
-            .json(&build_chat_completion_request(request, self.config()))
+            .json(&build_chat_completion_request_for_base_url(
+                request,
+                self.config(),
+                &self.base_url,
+            ))
             .send()
             .await
             .map_err(ApiError::from)
@@ -882,10 +887,50 @@ fn strip_routing_prefix(model: &str) -> &str {
     }
 }
 
+fn wire_model_for_base_url<'a>(
+    model: &'a str,
+    config: OpenAiCompatConfig,
+    base_url: &str,
+) -> Cow<'a, str> {
+    let Some(pos) = model.find('/') else {
+        return Cow::Borrowed(model);
+    };
+    let prefix = &model[..pos];
+    let lowered_prefix = prefix.to_ascii_lowercase();
+
+    if lowered_prefix == "openai" {
+        let trimmed_base_url = base_url.trim_end_matches('/');
+        let default_openai = DEFAULT_OPENAI_BASE_URL.trim_end_matches('/');
+        if config.provider_name == "OpenAI" && trimmed_base_url != default_openai {
+            // OpenAI-compatible gateways such as OpenRouter commonly use
+            // slash-containing model slugs (for example `openai/gpt-4.1-mini`).
+            // Preserve the slug when the user configured a non-default OpenAI
+            // base URL; the prefix still routed to the OpenAI-compatible client,
+            // but the gateway owns the final model namespace.
+            return Cow::Borrowed(model);
+        }
+        return Cow::Borrowed(&model[pos + 1..]);
+    }
+
+    if matches!(lowered_prefix.as_str(), "xai" | "grok" | "qwen" | "kimi") {
+        return Cow::Borrowed(&model[pos + 1..]);
+    }
+
+    Cow::Borrowed(model)
+}
+
 /// Estimate the serialized JSON size of a request payload in bytes.
 /// This is a pre-flight check to avoid hitting provider-specific size limits.
 pub fn estimate_request_body_size(request: &MessageRequest, config: OpenAiCompatConfig) -> usize {
-    let payload = build_chat_completion_request(request, config);
+    estimate_request_body_size_for_base_url(request, config, &read_base_url(config))
+}
+
+fn estimate_request_body_size_for_base_url(
+    request: &MessageRequest,
+    config: OpenAiCompatConfig,
+    base_url: &str,
+) -> usize {
+    let payload = build_chat_completion_request_for_base_url(request, config, base_url);
     // serde_json::to_vec gives us the exact byte size of the serialized JSON
     serde_json::to_vec(&payload).map_or(0, |v| v.len())
 }
@@ -897,7 +942,15 @@ pub fn check_request_body_size(
     request: &MessageRequest,
     config: OpenAiCompatConfig,
 ) -> Result<(), ApiError> {
-    let estimated_bytes = estimate_request_body_size(request, config);
+    check_request_body_size_for_base_url(request, config, &read_base_url(config))
+}
+
+fn check_request_body_size_for_base_url(
+    request: &MessageRequest,
+    config: OpenAiCompatConfig,
+    base_url: &str,
+) -> Result<(), ApiError> {
+    let estimated_bytes = estimate_request_body_size_for_base_url(request, config, base_url);
     let max_bytes = config.max_request_body_bytes;
 
     if estimated_bytes > max_bytes {
@@ -916,6 +969,14 @@ pub fn check_request_body_size(
 pub fn build_chat_completion_request(
     request: &MessageRequest,
     config: OpenAiCompatConfig,
+) -> Value {
+    build_chat_completion_request_for_base_url(request, config, &read_base_url(config))
+}
+
+fn build_chat_completion_request_for_base_url(
+    request: &MessageRequest,
+    config: OpenAiCompatConfig,
+    base_url: &str,
 ) -> Value {
     let mut messages = Vec::new();
     if let Some(system) = request.system.as_ref().filter(|value| !value.is_empty()) {
@@ -924,8 +985,10 @@ pub fn build_chat_completion_request(
             "content": system,
         }));
     }
-    // Strip routing prefix (e.g., "openai/gpt-4" → "gpt-4") for the wire.
-    let wire_model = strip_routing_prefix(&request.model);
+    // Resolve the transport routing prefix into the wire model. Custom
+    // OpenAI-compatible gateways may require slash-containing slugs intact.
+    let wire_model = wire_model_for_base_url(&request.model, config, base_url);
+    let wire_model = wire_model.as_ref();
     for message in &request.messages {
         messages.extend(translate_message(message, wire_model));
     }
@@ -994,9 +1057,29 @@ pub fn build_chat_completion_request(
         payload["reasoning_effort"] = json!(effort);
     }
 
+    for (key, value) in &request.extra_body {
+        if is_protected_extra_body_key(key) {
+            continue;
+        }
+        payload[key] = value.clone();
+    }
+
     payload
 }
 
+fn is_protected_extra_body_key(key: &str) -> bool {
+    matches!(
+        key,
+        "model"
+            | "messages"
+            | "stream"
+            | "tools"
+            | "tool_choice"
+            | "max_tokens"
+            | "max_completion_tokens"
+    )
+}
+
 /// Returns true for models that do NOT support the `is_error` field in tool results.
 /// kimi models (via Moonshot AI/Dashscope) reject this field with 400 Bad Request.
 /// Returns true for models that do NOT support the `is_error` field in tool results.
diff --git a/rust/crates/api/src/types.rs b/rust/crates/api/src/types.rs
index 0d41db19..3ec7f879 100644
--- a/rust/crates/api/src/types.rs
+++ b/rust/crates/api/src/types.rs
@@ -1,3 +1,5 @@
+use std::collections::BTreeMap;
+
 use runtime::{pricing_for_model, TokenUsage, UsageCostEstimate};
 use serde::{Deserialize, Serialize};
 use serde_json::Value;
@@ -31,6 +33,14 @@ pub struct MessageRequest {
     /// Silently ignored by backends that do not support it.
     #[serde(skip_serializing_if = "Option::is_none")]
     pub reasoning_effort: Option<String>,
+    /// Provider-specific OpenAI-compatible request body parameters. These are
+    /// copied into the final JSON payload after core fields are populated so
+    /// users can opt into gateway features such as `web_search_options`,
+    /// `parallel_tool_calls`, or custom local-server switches without waiting
+    /// for first-class typed fields. Core protocol keys are protected and cannot
+    /// be overridden through this map.
+    #[serde(default, skip_serializing_if = "BTreeMap::is_empty")]
+    pub extra_body: BTreeMap<String, Value>,
 }
 
 impl MessageRequest {