diff --git a/packages/llm/src/llm.ts b/packages/llm/src/llm.ts
index 8ade8a0d0d..e8f80e6276 100644
--- a/packages/llm/src/llm.ts
+++ b/packages/llm/src/llm.ts
@@ -47,6 +47,7 @@ export type ToolChoiceInput =
   | ConstructorParameters<typeof ToolChoice>[0]
   | ToolDefinition
   | string
+export type ToolChoiceMode = Exclude<ToolChoice["type"], "tool">
 
 export type ToolResultInput = Omit<ToolResultPart, "type" | "result"> & {
   readonly result: unknown
@@ -111,7 +112,7 @@ export const model = (input: ModelInput) => {
   })
 }
 
-export const tool = (input: ToolDefinition | ConstructorParameters<typeof ToolDefinition>[0]) => {
+export const toolDefinition = (input: ToolDefinition | ConstructorParameters<typeof ToolDefinition>[0]) => {
   if (input instanceof ToolDefinition) return input
   return new ToolDefinition(input)
 }
@@ -141,10 +142,15 @@ export const toolResult = (input: ToolResultInput): ToolResultPart => ({
 export const toolMessage = (input: ToolResultPart | ToolResultInput) =>
   message({ role: "tool", content: ["type" in input ? input : toolResult(input)] })
 
+export const toolChoiceName = (name: string) => new ToolChoice({ type: "tool", name })
+
+const isToolChoiceMode = (value: string): value is ToolChoiceMode =>
+  value === "auto" || value === "none" || value === "required"
+
 export const toolChoice = (input: ToolChoiceInput) => {
   if (input instanceof ToolChoice) return input
   if (input instanceof ToolDefinition) return new ToolChoice({ type: "tool", name: input.name })
-  if (typeof input === "string") return new ToolChoice({ type: "tool", name: input })
+  if (typeof input === "string") return isToolChoiceMode(input) ? new ToolChoice({ type: input }) : toolChoiceName(input)
   return new ToolChoice(input)
 }
 
@@ -159,7 +165,7 @@ export const request = (input: RequestInput) => {
     ...rest,
     system: systemParts(requestSystem),
     messages: [...(messages?.map(message) ?? []), ...(prompt === undefined ? [] : [user(prompt)])],
-    tools: tools?.map(tool) ?? [],
+    tools: tools?.map(toolDefinition) ?? [],
     toolChoice: requestToolChoice ? toolChoice(requestToolChoice) : undefined,
     generation: generation(requestGeneration),
   })
diff --git a/packages/llm/test/llm.test.ts b/packages/llm/test/llm.test.ts
index 0150c782d5..807f342034 100644
--- a/packages/llm/test/llm.test.ts
+++ b/packages/llm/test/llm.test.ts
@@ -21,13 +21,25 @@ describe("llm constructors", () => {
   })
 
   test("builds tool choices from names and tools", () => {
-    const tool = LLM.tool({ name: "lookup", description: "Lookup data", inputSchema: { type: "object" } })
+    const tool = LLM.toolDefinition({ name: "lookup", description: "Lookup data", inputSchema: { type: "object" } })
 
     expect(tool).toBeInstanceOf(ToolDefinition)
     expect(LLM.toolChoice("lookup")).toEqual(new ToolChoice({ type: "tool", name: "lookup" }))
+    expect(LLM.toolChoiceName("required")).toEqual(new ToolChoice({ type: "tool", name: "required" }))
     expect(LLM.toolChoice(tool)).toEqual(new ToolChoice({ type: "tool", name: "lookup" }))
   })
 
+  test("builds tool choice modes from reserved strings", () => {
+    expect(LLM.toolChoice("auto")).toEqual(new ToolChoice({ type: "auto" }))
+    expect(LLM.toolChoice("none")).toEqual(new ToolChoice({ type: "none" }))
+    expect(LLM.toolChoice("required")).toEqual(new ToolChoice({ type: "required" }))
+    expect(LLM.request({
+      model: LLM.model({ id: "fake-model", provider: "fake", protocol: "openai-chat" }),
+      prompt: "Use tools if needed.",
+      toolChoice: "required",
+    }).toolChoice).toEqual(new ToolChoice({ type: "required" }))
+  })
+
   test("builds assistant tool calls and tool result messages", () => {
     const call = LLM.toolCall({ id: "call_1", name: "lookup", input: { query: "weather" } })
     const result = LLM.toolResult({ id: "call_1", name: "lookup", result: { temperature: 72 } })
diff --git a/packages/llm/test/provider/anthropic-messages.recorded.test.ts b/packages/llm/test/provider/anthropic-messages.recorded.test.ts
index 78d01f6e19..5e1a85e209 100644
--- a/packages/llm/test/provider/anthropic-messages.recorded.test.ts
+++ b/packages/llm/test/provider/anthropic-messages.recorded.test.ts
@@ -18,7 +18,7 @@ const request = LLM.request({
   generation: { maxTokens: 20, temperature: 0 },
 })
 
-const getWeather = LLM.tool({
+const getWeather = LLM.toolDefinition({
   name: "get_weather",
   description: "Get current weather for a city.",
   inputSchema: {
diff --git a/packages/llm/test/provider/gemini.recorded.test.ts b/packages/llm/test/provider/gemini.recorded.test.ts
index 5950a87c61..c4f21ff99e 100644
--- a/packages/llm/test/provider/gemini.recorded.test.ts
+++ b/packages/llm/test/provider/gemini.recorded.test.ts
@@ -18,7 +18,7 @@ const request = LLM.request({
   generation: { maxTokens: 80, temperature: 0 },
 })
 
-const getWeather = LLM.tool({
+const getWeather = LLM.toolDefinition({
   name: "get_weather",
   description: "Get current weather for a city.",
   inputSchema: {
diff --git a/packages/llm/test/provider/openai-chat.recorded.test.ts b/packages/llm/test/provider/openai-chat.recorded.test.ts
index cf3807778d..5e5a86c7dd 100644
--- a/packages/llm/test/provider/openai-chat.recorded.test.ts
+++ b/packages/llm/test/provider/openai-chat.recorded.test.ts
@@ -18,7 +18,7 @@ const request = LLM.request({
   generation: { maxTokens: 20, temperature: 0 },
 })
 
-const getWeather = LLM.tool({
+const getWeather = LLM.toolDefinition({
   name: "get_weather",
   description: "Get current weather for a city.",
   inputSchema: {
diff --git a/packages/llm/test/provider/openai-compatible-chat.recorded.test.ts b/packages/llm/test/provider/openai-compatible-chat.recorded.test.ts
index 414f5875c2..296429848c 100644
--- a/packages/llm/test/provider/openai-compatible-chat.recorded.test.ts
+++ b/packages/llm/test/provider/openai-compatible-chat.recorded.test.ts
@@ -31,7 +31,7 @@ const togetherRequest = LLM.request({
   generation: { maxTokens: 20, temperature: 0 },
 })
 
-const getWeather = LLM.tool({
+const getWeather = LLM.toolDefinition({
   name: "get_weather",
   description: "Get current weather for a city.",
   inputSchema: {
diff --git a/packages/opencode/src/session/llm-native.ts b/packages/opencode/src/session/llm-native.ts
index 41a53a9177..b5dc88ada8 100644
--- a/packages/opencode/src/session/llm-native.ts
+++ b/packages/opencode/src/session/llm-native.ts
@@ -160,7 +160,7 @@ const messages = (input: MessageV2.WithParts): ReadonlyArray<CoreMessage> => {
 }
 
 export const toolDefinition = (input: { readonly model: Provider.Model; readonly tool: Tool.Def }) =>
-  LLM.tool({
+  LLM.toolDefinition({
     name: input.tool.id,
     description: input.tool.description,
     inputSchema: EffectZod.toJsonSchema(input.tool.parameters),