refactor(core): scope variant id string to its branch

packages/client/src/generated/types.ts

@@ -1960,6 +1960,7 @@ export type ModelsListOutput = {
         }
     readonly capabilities: {
       readonly tools: boolean
+      readonly reasoning: boolean
       readonly input: ReadonlyArray<string>
       readonly output: ReadonlyArray<string>
     }

packages/core/src/config/plugin/provider.ts

@@ -66,6 +66,7 @@ export const Plugin = define({
                 if (config.capabilities !== undefined) {
                   model.capabilities = {
                     tools: config.capabilities.tools,
+                    reasoning: config.capabilities.reasoning,
                     input: [...config.capabilities.input],
                     output: [...config.capabilities.output],
                   }

packages/core/src/plugin/models-dev.ts

@@ -108,6 +108,7 @@ export const ModelsDevPlugin = define({
                   }
               draft.capabilities = {
                 tools: model.tool_call,
+                reasoning: model.reasoning,
                 input: [...(model.modalities?.input ?? [])],
                 output: [...(model.modalities?.output ?? [])],
               }

packages/core/src/plugin/provider/opencode.ts

@@ -135,6 +135,7 @@ export const OpencodePlugin = define<HttpClient.HttpClient | EventV2.Service | S
                 : { id: model.api.id, type: "native", url: config.provider.api, settings: {} }
             }
             if (config.tool_call !== undefined) model.capabilities.tools = config.tool_call
+            if (config.reasoning !== undefined) model.capabilities.reasoning = config.reasoning
             if (config.modalities?.input !== undefined) model.capabilities.input = [...config.modalities.input]
             if (config.modalities?.output !== undefined) model.capabilities.output = [...config.modalities.output]
             const packageName = config.provider?.npm ?? item.npm

packages/core/src/plugin/variant.ts

@@ -28,12 +28,36 @@ export const Plugin = define({
 })
 
 export function generate(model: ModelV2Info): ModelV2Info["variants"] {
-  if (model.api.type !== "aisdk" || model.api.package !== "@ai-sdk/openai-compatible") return []
-  const ids = `${model.id} ${model.api.id}`.toLowerCase()
-  if (!["glm-5.2", "glm-5-2", "glm-5p2"].some((name) => ids.includes(name))) return []
-  return ["high", "max"].map((id) => ({
-    id,
+  if (model.api.type !== "aisdk") return []
+
+  if (model.api.package === "@ai-sdk/openai-compatible") {
+    const ids = `${model.id} ${model.api.id}`.toLowerCase()
+    if (["glm-5.2", "glm-5-2", "glm-5p2"].some((name) => ids.includes(name)))
+      return ["high", "max"].map((id) => ({
+        id,
+        headers: {},
+        body: { reasoning_effort: id },
+      }))
+    return []
+  }
+
+  if (model.api.package === "@ai-sdk/anthropic") return anthropicThinking(model)
+
+  return []
+}
+
+// Anthropic thinking levels lower to the Messages API `thinking` body, which the
+// v2 Anthropic protocol only accepts as `{ type: "enabled", budget_tokens }`.
+// Budgets scale with the model output limit so the larger tier stays under the cap.
+function anthropicThinking(model: ModelV2Info): ModelV2Info["variants"] {
+  if (!model.capabilities.reasoning) return []
+  const budget = (target: number) => Math.max(1024, Math.min(target, model.limit.output - 1))
+  return [
+    { id: "high", target: 16_000 },
+    { id: "max", target: 31_999 },
+  ].map((tier) => ({
+    id: tier.id,
     headers: {},
-    body: { reasoning_effort: id },
+    body: { thinking: { type: "enabled", budget_tokens: budget(tier.target) } },
   }))
 }

packages/core/src/v1/config/migrate.ts

@@ -211,8 +211,16 @@ function migrateModel(info: typeof ConfigProviderV1.Model.Type, packageName?: st
       : []),
   ]
   const capabilities =
-    info.tool_call !== undefined || info.modalities?.input !== undefined || info.modalities?.output !== undefined
-      ? { tools: info.tool_call ?? false, input: info.modalities?.input ?? [], output: info.modalities?.output ?? [] }
+    info.tool_call !== undefined ||
+    info.reasoning !== undefined ||
+    info.modalities?.input !== undefined ||
+    info.modalities?.output !== undefined
+      ? {
+          tools: info.tool_call ?? false,
+          reasoning: info.reasoning ?? false,
+          input: info.modalities?.input ?? [],
+          output: info.modalities?.output ?? [],
+        }
       : undefined
   return {
     family: info.family,

packages/core/test/config/provider.test.ts

@@ -174,7 +174,7 @@ describe("ConfigProviderPlugin.Plugin", () => {
                       models: {
                         chat: {
                           name: "First",
-                          capabilities: { tools: true, input: ["text"], output: ["text"] },
+                          capabilities: { tools: true, reasoning: false, input: ["text"], output: ["text"] },
                           disabled: true,
                           limit: { context: 100, output: 50 },
                           cost: { input: 1, output: 2 },
@@ -251,7 +251,7 @@ describe("ConfigProviderPlugin.Plugin", () => {
         expect(provider.request.headers).toEqual({ first: "first", shared: "last", last: "last" })
         expect(model.api.id).toBe(ModelV2.ID.make("api-chat"))
         expect(model.name).toBe("Last")
-        expect(model.capabilities).toEqual({ tools: true, input: ["text"], output: ["text"] })
+        expect(model.capabilities).toEqual({ tools: true, reasoning: false, input: ["text"], output: ["text"] })
         expect(model.enabled).toBe(false)
         expect(model.limit).toEqual({ context: 100, output: 75 })
         expect(model.cost).toEqual([{ input: 1, output: 2, cache: { read: 0, write: 0 }, tier: undefined }])

packages/core/test/plugin/provider-opencode.test.ts

@@ -111,6 +111,7 @@ describe("OpencodePlugin", () => {
                           family: "remote",
                           release_date: "2026-01-02",
                           tool_call: true,
+                          reasoning: true,
                           modalities: { input: ["text", "image"], output: ["text"] },
                           options: { apiKey: "model-secret", temperature: 0.5 },
                           variants: { high: { apiKey: "variant-secret", temperature: 0.2 } },
@@ -170,7 +171,7 @@ describe("OpencodePlugin", () => {
           expect(model).toMatchObject({
             name: "Remote Model",
             family: "remote",
-            capabilities: { tools: true, input: ["text", "image"], output: ["text"] },
+            capabilities: { tools: true, reasoning: true, input: ["text", "image"], output: ["text"] },
             cost: [{ input: 1, output: 2, cache: { read: 0.1, write: 0 } }],
             limit: { context: 1000, output: 100 },
           })

packages/core/test/plugin/variant.test.ts

@@ -76,4 +76,73 @@ describe("VariantPlugin", () => {
       ])
     }),
   )
+
+  it.effect("adds Anthropic thinking variants for reasoning models", () =>
+    Effect.gen(function* () {
+      const service = yield* Catalog.Service
+      yield* service.transform((catalog) => {
+        catalog.model.update(ProviderV2.ID.opencode, ModelV2.ID.make("claude-opus-4-8"), (model) => {
+          model.api = {
+            id: ModelV2.ID.make("claude-opus-4-8"),
+            type: "aisdk",
+            package: "@ai-sdk/anthropic",
+          }
+          model.capabilities.reasoning = true
+          model.limit = { context: 200_000, output: 64_000 }
+        })
+      })
+      yield* VariantPlugin.Plugin.effect(host({ catalog: catalogHost(service) }))
+
+      expect((yield* service.model.get(ProviderV2.ID.opencode, ModelV2.ID.make("claude-opus-4-8")))?.variants).toEqual([
+        expect.objectContaining({ id: "high", body: { thinking: { type: "enabled", budget_tokens: 16_000 } } }),
+        expect.objectContaining({ id: "max", body: { thinking: { type: "enabled", budget_tokens: 31_999 } } }),
+      ])
+    }),
+  )
+
+  it.effect("clamps Anthropic thinking budgets to the output limit", () =>
+    Effect.gen(function* () {
+      const service = yield* Catalog.Service
+      yield* service.transform((catalog) => {
+        catalog.model.update(ProviderV2.ID.opencode, ModelV2.ID.make("claude-haiku-4-5"), (model) => {
+          model.api = {
+            id: ModelV2.ID.make("claude-haiku-4-5"),
+            type: "aisdk",
+            package: "@ai-sdk/anthropic",
+          }
+          model.capabilities.reasoning = true
+          model.limit = { context: 200_000, output: 8_000 }
+        })
+      })
+      yield* VariantPlugin.Plugin.effect(host({ catalog: catalogHost(service) }))
+
+      expect((yield* service.model.get(ProviderV2.ID.opencode, ModelV2.ID.make("claude-haiku-4-5")))?.variants).toEqual(
+        [
+          expect.objectContaining({ id: "high", body: { thinking: { type: "enabled", budget_tokens: 7_999 } } }),
+          expect.objectContaining({ id: "max", body: { thinking: { type: "enabled", budget_tokens: 7_999 } } }),
+        ],
+      )
+    }),
+  )
+
+  it.effect("skips Anthropic models without reasoning capability", () =>
+    Effect.gen(function* () {
+      const service = yield* Catalog.Service
+      yield* service.transform((catalog) => {
+        catalog.model.update(ProviderV2.ID.opencode, ModelV2.ID.make("claude-3-5-haiku"), (model) => {
+          model.api = {
+            id: ModelV2.ID.make("claude-3-5-haiku"),
+            type: "aisdk",
+            package: "@ai-sdk/anthropic",
+          }
+          model.capabilities.reasoning = false
+        })
+      })
+      yield* VariantPlugin.Plugin.effect(host({ catalog: catalogHost(service) }))
+
+      expect((yield* service.model.get(ProviderV2.ID.opencode, ModelV2.ID.make("claude-3-5-haiku")))?.variants).toEqual(
+        [],
+      )
+    }),
+  )
 })

packages/core/test/session-runner-model.test.ts

@@ -28,7 +28,7 @@ const model = (api: Api, variants: ModelV2.Info["variants"] = []) =>
     providerID: ProviderV2.ID.make("test-provider"),
     name: "Test model",
     api: { id: ModelV2.ID.make("api-test-model"), ...api },
-    capabilities: { tools: true, input: ["text"], output: ["text"] },
+    capabilities: { tools: true, reasoning: false, input: ["text"], output: ["text"] },
     request: {
       headers: { "x-test": "header" },
       body: { apiKey: "secret", custom_extension: { enabled: true } },

packages/schema/src/model.ts

@@ -24,6 +24,7 @@ export type Family = typeof Family.Type
 export interface Capabilities extends Schema.Schema.Type<typeof Capabilities> {}
 export const Capabilities = Schema.Struct({
   tools: Schema.Boolean,
+  reasoning: Schema.Boolean,
   input: Schema.Array(Schema.String),
   output: Schema.Array(Schema.String),
 }).annotate({ identifier: "Model.Capabilities" })
@@ -93,7 +94,7 @@ export const Info = Schema.Struct({
           providerID,
           name: modelID,
           api: { id: modelID, type: "native", settings: {} },
-          capabilities: { tools: false, input: [], output: [] },
+          capabilities: { tools: false, reasoning: false, input: [], output: [] },
           request: { headers: {}, body: {} },
           variants: [],
           time: { released: 0 },

packages/sdk/js/src/v2/gen/types.gen.ts

@@ -4787,6 +4787,7 @@ export type ModelApi =
 
 export type ModelCapabilities = {
   tools: boolean
+  reasoning: boolean
   input: Array<string>
   output: Array<string>
 }

packages/sdk/openapi.json

@@ -29767,6 +29767,9 @@
           "tools": {
             "type": "boolean"
           },
+          "reasoning": {
+            "type": "boolean"
+          },
           "input": {
             "type": "array",
             "items": {
@@ -29780,7 +29783,7 @@
             }
           }
         },
-        "required": ["tools", "input", "output"],
+        "required": ["tools", "reasoning", "input", "output"],
         "additionalProperties": false
       },
       "ModelCost": {