diff --git a/crates/goose/src/config/declarative_providers.rs b/crates/goose/src/config/declarative_providers.rs
index acd35714..e0da2d56 100644
--- a/crates/goose/src/config/declarative_providers.rs
+++ b/crates/goose/src/config/declarative_providers.rs
@@ -7,7 +7,16 @@ use crate::providers::openai::OpenAiProvider;
 use anyhow::Result;
 use include_dir::{include_dir, Dir};
 use once_cell::sync::Lazy;
-use serde::{Deserialize, Serialize};
+use serde::{Deserialize, Deserializer, Serialize};
+
+/// Deserialize an optional string, treating empty/whitespace-only values as None.
+fn deserialize_non_empty_string<'de, D>(deserializer: D) -> Result<Option<String>, D::Error>
+where
+    D: Deserializer<'de>,
+{
+    let opt: Option<String> = Option::deserialize(deserializer)?;
+    Ok(opt.filter(|s| !s.trim().is_empty()))
+}
 use std::collections::HashMap;
 use std::path::Path;
 use std::sync::Mutex;
@@ -66,6 +75,8 @@ pub struct DeclarativeProviderConfig {
     pub dynamic_models: Option<bool>,
     #[serde(default)]
     pub skip_canonical_filtering: bool,
+    #[serde(default, deserialize_with = "deserialize_non_empty_string")]
+    pub fast_model: Option<String>,
 }
 
 fn default_requires_auth() -> bool {
@@ -221,6 +232,7 @@ pub fn create_custom_provider(
         env_vars: None,
         dynamic_models: None,
         skip_canonical_filtering: false,
+        fast_model: None,
     };
 
     let custom_providers_dir = custom_providers_dir();
@@ -287,6 +299,7 @@ pub fn update_custom_provider(params: UpdateCustomProviderParams) -> Result<()>
             env_vars: existing_config.env_vars,
             dynamic_models: existing_config.dynamic_models,
             skip_canonical_filtering: existing_config.skip_canonical_filtering,
+            fast_model: existing_config.fast_model.clone(),
         };
 
         let file_path = custom_providers_dir().join(format!("{}.json", updated_config.name));
diff --git a/crates/goose/src/providers/anthropic.rs b/crates/goose/src/providers/anthropic.rs
index a446797d..43039d3e 100644
--- a/crates/goose/src/providers/anthropic.rs
+++ b/crates/goose/src/providers/anthropic.rs
@@ -127,6 +127,12 @@ impl AnthropicProvider {
             None
         };
 
+        let model = if let Some(ref fast_model_name) = config.fast_model {
+            model.with_fast(fast_model_name, &config.name)?
+        } else {
+            model
+        };
+
         Ok(Self {
             api_client,
             model,
diff --git a/crates/goose/src/providers/ollama.rs b/crates/goose/src/providers/ollama.rs
index 5678a1da..4dceb3ab 100644
--- a/crates/goose/src/providers/ollama.rs
+++ b/crates/goose/src/providers/ollama.rs
@@ -182,6 +182,12 @@ impl OllamaProvider {
             ));
         }
 
+        let model = if let Some(ref fast_model_name) = config.fast_model {
+            model.with_fast(fast_model_name, &config.name)?
+        } else {
+            model
+        };
+
         Ok(Self {
             api_client,
             model,
diff --git a/crates/goose/src/providers/openai.rs b/crates/goose/src/providers/openai.rs
index d7d26177..aad6ddd0 100644
--- a/crates/goose/src/providers/openai.rs
+++ b/crates/goose/src/providers/openai.rs
@@ -221,6 +221,12 @@ impl OpenAiProvider {
             None
         };
 
+        let model = if let Some(ref fast_model_name) = config.fast_model {
+            model.with_fast(fast_model_name, &config.name)?
+        } else {
+            model
+        };
+
         Ok(Self {
             api_client,
             base_path,
diff --git a/ui/desktop/openapi.json b/ui/desktop/openapi.json
index db75a237..1f6b7b05 100644
--- a/ui/desktop/openapi.json
+++ b/ui/desktop/openapi.json
@@ -4618,6 +4618,10 @@
             },
             "nullable": true
           },
+          "fast_model": {
+            "type": "string",
+            "nullable": true
+          },
           "headers": {
             "type": "object",
             "additionalProperties": {
diff --git a/ui/desktop/src/api/types.gen.ts b/ui/desktop/src/api/types.gen.ts
index 19065eee..902e3e86 100644
--- a/ui/desktop/src/api/types.gen.ts
+++ b/ui/desktop/src/api/types.gen.ts
@@ -216,6 +216,7 @@ export type DeclarativeProviderConfig = {
     dynamic_models?: boolean | null;
     engine: ProviderEngine;
     env_vars?: Array<EnvVarConfig> | null;
+    fast_model?: string | null;
     headers?: {
         [key: string]: string;
     } | null;