diff --git a/packages/core/src/models-dev.ts b/packages/core/src/models-dev.ts
index 202943a2f..63e0a6f70 100644
--- a/packages/core/src/models-dev.ts
+++ b/packages/core/src/models-dev.ts
@@ -49,6 +49,7 @@ export const Model = Schema.Struct({
   reasoning: Schema.Boolean,
   temperature: Schema.Boolean,
   tool_call: Schema.Boolean,
+  tool_choice_required: Schema.optional(Schema.Boolean),
   interleaved: Schema.optional(
     Schema.Union([
       Schema.Literal(true),
diff --git a/packages/opencode/src/config/provider.ts b/packages/opencode/src/config/provider.ts
index 5635512ce..19408c706 100644
--- a/packages/opencode/src/config/provider.ts
+++ b/packages/opencode/src/config/provider.ts
@@ -11,6 +11,7 @@ export const Model = Schema.Struct({
   reasoning: Schema.optional(Schema.Boolean),
   temperature: Schema.optional(Schema.Boolean),
   tool_call: Schema.optional(Schema.Boolean),
+  tool_choice_required: Schema.optional(Schema.Boolean),
   interleaved: Schema.optional(
     Schema.Union([
       Schema.Literal(true),
diff --git a/packages/opencode/src/provider/provider.ts b/packages/opencode/src/provider/provider.ts
index 2a778fd64..3492ef77a 100644
--- a/packages/opencode/src/provider/provider.ts
+++ b/packages/opencode/src/provider/provider.ts
@@ -867,6 +867,7 @@ const ProviderCapabilities = Schema.Struct({
   reasoning: Schema.Boolean,
   attachment: Schema.Boolean,
   toolcall: Schema.Boolean,
+  toolChoiceRequired: Schema.optional(Schema.Boolean),
   input: ProviderModalities,
   output: ProviderModalities,
   interleaved: ProviderInterleaved,
@@ -1068,6 +1069,7 @@ function fromModelsDevModel(provider: ModelsDev.Provider, model: ModelsDev.Model
       reasoning: model.reasoning ?? false,
       attachment: model.attachment ?? false,
       toolcall: model.tool_call ?? true,
+      toolChoiceRequired: model.tool_choice_required ?? true,
       input: {
         text: model.modalities?.input?.includes("text") ?? false,
         audio: model.modalities?.input?.includes("audio") ?? false,
@@ -1296,6 +1298,7 @@ export const layer = Layer.effect(
                 reasoning: model.reasoning ?? existingModel?.capabilities.reasoning ?? false,
                 attachment: model.attachment ?? existingModel?.capabilities.attachment ?? false,
                 toolcall: model.tool_call ?? existingModel?.capabilities.toolcall ?? true,
+                toolChoiceRequired: model.tool_choice_required ?? existingModel?.capabilities.toolChoiceRequired ?? true,
                 input: {
                   text: model.modalities?.input?.includes("text") ?? existingModel?.capabilities.input.text ?? true,
                   audio: model.modalities?.input?.includes("audio") ?? existingModel?.capabilities.input.audio ?? false,
diff --git a/packages/opencode/src/session/prompt.ts b/packages/opencode/src/session/prompt.ts
index c09ee8628..5f0d24419 100644
--- a/packages/opencode/src/session/prompt.ts
+++ b/packages/opencode/src/session/prompt.ts
@@ -1436,7 +1436,12 @@ export const layer = Layer.effect(
               messages: [...modelMsgs, ...(isLastStep ? [{ role: "assistant" as const, content: MAX_STEPS }] : [])],
               tools,
               model,
-              toolChoice: format.type === "json_schema" ? "required" : undefined,
+              toolChoice:
+                format.type === "json_schema"
+                  ? model.capabilities.toolChoiceRequired === false
+                    ? "auto"
+                    : "required"
+                  : undefined,
             })
 
             if (structured !== undefined) {
diff --git a/packages/opencode/test/provider/provider.test.ts b/packages/opencode/test/provider/provider.test.ts
index 5215b094a..1185863bc 100644
--- a/packages/opencode/test/provider/provider.test.ts
+++ b/packages/opencode/test/provider/provider.test.ts
@@ -757,6 +757,7 @@ test("model inherits properties from existing database model", async () => {
       const model = providers[ProviderID.anthropic].models["claude-sonnet-4-20250514"]
       expect(model.name).toBe("Custom Name for Sonnet")
       expect(model.capabilities.toolcall).toBe(true)
+      expect(model.capabilities.toolChoiceRequired).toBe(true)
       expect(model.capabilities.attachment).toBe(true)
       expect(model.limit.context).toBeGreaterThan(0)
     },
@@ -1376,6 +1377,44 @@ test("model defaults tool_call to true when not specified", async () => {
   })
 })
 
+test("model can disable required tool_choice separately from tool_call", async () => {
+  await using tmp = await tmpdir({
+    init: async (dir) => {
+      await Bun.write(
+        path.join(dir, "opencode.json"),
+        JSON.stringify({
+          $schema: "https://opencode.ai/config.json",
+          provider: {
+            "tool-choice": {
+              name: "Tool Choice Provider",
+              npm: "@ai-sdk/openai-compatible",
+              env: [],
+              models: {
+                model: {
+                  name: "Model",
+                  tool_call: true,
+                  tool_choice_required: false,
+                  limit: { context: 4000, output: 1000 },
+                },
+              },
+              options: { apiKey: "test" },
+            },
+          },
+        }),
+      )
+    },
+  })
+  await withTestInstance({
+    directory: tmp.path,
+    fn: async (ctx) => {
+      const providers = await list(ctx)
+      const model = providers[ProviderID.make("tool-choice")].models.model
+      expect(model.capabilities.toolcall).toBe(true)
+      expect(model.capabilities.toolChoiceRequired).toBe(false)
+    },
+  })
+})
+
 test("model headers are preserved", async () => {
   await using tmp = await tmpdir({
     init: async (dir) => {
@@ -2018,6 +2057,7 @@ test("models.dev normalization fills required response fields", () => {
   expect(model.capabilities.reasoning).toBe(false)
   expect(model.capabilities.attachment).toBe(false)
   expect(model.capabilities.toolcall).toBe(true)
+  expect(model.capabilities.toolChoiceRequired).toBe(true)
   expect(model.release_date).toBe("")
 })
 
diff --git a/packages/opencode/test/session/prompt.test.ts b/packages/opencode/test/session/prompt.test.ts
index ff9ded4d1..e3abeffd2 100644
--- a/packages/opencode/test/session/prompt.test.ts
+++ b/packages/opencode/test/session/prompt.test.ts
@@ -294,6 +294,30 @@ function providerCfg(url: string) {
   }
 }
 
+function toolChoiceRequiredDisabledProviderCfg(url: string) {
+  return {
+    ...providerCfg(url),
+    provider: {
+      test: {
+        ...cfg.provider.test,
+        models: {
+          ...cfg.provider.test.models,
+          "tool-choice-disabled": {
+            ...cfg.provider.test.models["test-model"],
+            id: "tool-choice-disabled",
+            name: "Tool Choice Disabled",
+            tool_choice_required: false,
+          },
+        },
+        options: {
+          ...cfg.provider.test.options,
+          baseURL: url,
+        },
+      },
+    },
+  }
+}
+
 const writeText = Effect.fn("test.writeText")(function* (file: string, text: string) {
   const fs = yield* AppFileSystem.Service
   yield* fs.writeWithDirs(file, text)
@@ -482,6 +506,43 @@ it.instance("loop calls LLM and returns assistant message", () =>
   }),
 )
 
+it.instance("structured output uses auto tool choice when model disables required tool choice", () =>
+  Effect.gen(function* () {
+    const { llm } = yield* useServerConfig(toolChoiceRequiredDisabledProviderCfg)
+    const prompt = yield* SessionPrompt.Service
+    const sessions = yield* Session.Service
+    const chat = yield* sessions.create({
+      title: "Pinned",
+      permission: [{ permission: "*", pattern: "*", action: "allow" }],
+    })
+    yield* llm.text("plain text")
+
+    yield* prompt.prompt({
+      sessionID: chat.id,
+      agent: "build",
+      model: { providerID: ProviderID.make("test"), modelID: ModelID.make("tool-choice-disabled") },
+      parts: [{ type: "text", text: "say hello" }],
+      format: {
+        type: "json_schema",
+        schema: {
+          type: "object",
+          properties: { answer: { type: "string" } },
+          required: ["answer"],
+        },
+      },
+    })
+
+    const inputs = yield* llm.inputs
+    expect(inputs).toHaveLength(1)
+    expect(inputs[0].tool_choice).toBe("auto")
+    expect(inputs[0].tools).toEqual(
+      expect.arrayContaining([
+        expect.objectContaining({ function: expect.objectContaining({ name: "StructuredOutput" }) }),
+      ]),
+    )
+  }),
+)
+
 noLLMServer.instance(
   "prompt emits v2 prompted and synthetic events",
   () =>
diff --git a/packages/opencode/test/tool/fixtures/models-api.json b/packages/opencode/test/tool/fixtures/models-api.json
index 6302a951d..b89caf7c7 100644
--- a/packages/opencode/test/tool/fixtures/models-api.json
+++ b/packages/opencode/test/tool/fixtures/models-api.json
@@ -58320,6 +58320,7 @@
         "attachment": false,
         "reasoning": true,
         "tool_call": true,
+        "tool_choice_required": false,
         "interleaved": {
           "field": "reasoning_content"
         },
diff --git a/packages/sdk/js/src/gen/types.gen.ts b/packages/sdk/js/src/gen/types.gen.ts
index 5e4fd8906..f2ba12309 100644
--- a/packages/sdk/js/src/gen/types.gen.ts
+++ b/packages/sdk/js/src/gen/types.gen.ts
@@ -1044,6 +1044,7 @@ export type ProviderConfig = {
       reasoning?: boolean
       temperature?: boolean
       tool_call?: boolean
+      tool_choice_required?: boolean
       cost?: {
         input: number
         output: number
diff --git a/packages/sdk/js/src/v2/gen/types.gen.ts b/packages/sdk/js/src/v2/gen/types.gen.ts
index d0a82a5b0..0e8749bac 100644
--- a/packages/sdk/js/src/v2/gen/types.gen.ts
+++ b/packages/sdk/js/src/v2/gen/types.gen.ts
@@ -1049,6 +1049,7 @@ export type ProviderConfig = {
       reasoning?: boolean
       temperature?: boolean
       tool_call?: boolean
+      tool_choice_required?: boolean
       interleaved?:
         | true
         | {
@@ -1313,6 +1314,7 @@ export type Model = {
     reasoning: boolean
     attachment: boolean
     toolcall: boolean
+    toolChoiceRequired?: boolean
     input: {
       text: boolean
       audio: boolean