diff --git a/packages/opencode/src/effect/runtime-flags.ts b/packages/opencode/src/effect/runtime-flags.ts
index b1b8ab25ac..565f6b1631 100644
--- a/packages/opencode/src/effect/runtime-flags.ts
+++ b/packages/opencode/src/effect/runtime-flags.ts
@@ -23,6 +23,11 @@ export class Service extends ConfigService.Service<Service>()("@opencode/Runtime
   experimentalLspTool: enabledByExperimental("OPENCODE_EXPERIMENTAL_LSP_TOOL"),
   experimentalPlanMode: enabledByExperimental("OPENCODE_EXPERIMENTAL_PLAN_MODE"),
   experimentalEventSystem: enabledByExperimental("OPENCODE_EXPERIMENTAL_EVENT_SYSTEM"),
+  experimentalNativeLlm: Config.all({
+    experimental,
+    enabled: bool("OPENCODE_EXPERIMENTAL_NATIVE_LLM"),
+    legacy: Config.string("OPENCODE_LLM_RUNTIME").pipe(Config.withDefault("")),
+  }).pipe(Config.map((flags) => flags.experimental || flags.enabled || flags.legacy === "native")),
   client: Config.string("OPENCODE_CLIENT").pipe(Config.withDefault("cli")),
 }) {}
 
diff --git a/packages/opencode/src/session/llm.ts b/packages/opencode/src/session/llm.ts
index 87d2e3973d..4a43423951 100644
--- a/packages/opencode/src/session/llm.ts
+++ b/packages/opencode/src/session/llm.ts
@@ -29,6 +29,7 @@ import * as Option from "effect/Option"
 import * as OtelTracer from "@effect/opentelemetry/Tracer"
 import { LLMAISDK } from "./llm/ai-sdk"
 import { LLMNativeRuntime } from "./llm/native-runtime"
+import { RuntimeFlags } from "@/effect/runtime-flags"
 
 const log = Log.create({ service: "llm" })
 export const OUTPUT_TOKEN_MAX = ProviderTransform.OUTPUT_TOKEN_MAX
@@ -37,8 +38,6 @@ export const OUTPUT_TOKEN_MAX = ProviderTransform.OUTPUT_TOKEN_MAX
 const mergeOptions = (target: Record<string, any>, source: Record<string, any> | undefined): Record<string, any> =>
   mergeDeep(target, source ?? {}) as Record<string, any>
 
-const runtime = () => (process.env.OPENCODE_LLM_RUNTIME === "native" ? "native" : "ai-sdk")
-
 export type StreamInput = {
   user: MessageV2.User
   sessionID: string
@@ -67,7 +66,13 @@ export class Service extends Context.Service<Service, Interface>()("@opencode/LL
 const live: Layer.Layer<
   Service,
   never,
-  Auth.Service | Config.Service | Provider.Service | Plugin.Service | Permission.Service | LLMClientService
+  | Auth.Service
+  | Config.Service
+  | Provider.Service
+  | Plugin.Service
+  | Permission.Service
+  | LLMClientService
+  | RuntimeFlags.Service
 > = Layer.effect(
   Service,
   Effect.gen(function* () {
@@ -77,6 +82,7 @@ const live: Layer.Layer<
     const plugin = yield* Plugin.Service
     const perm = yield* Permission.Service
     const llmClient = yield* LLMClient.Service
+    const flags = yield* RuntimeFlags.Service
 
     const run = Effect.fn("LLM.run")(function* (input: StreamRequest) {
       const l = log
@@ -357,7 +363,7 @@ const live: Layer.Layer<
         ...headers,
       }
 
-      if (runtime() === "native") {
+      if (flags.experimentalNativeLlm) {
         const native = LLMNativeRuntime.stream({
           model: input.model,
           provider: item,
@@ -491,6 +497,7 @@ export const defaultLayer = Layer.suspend(() =>
     Layer.provide(Provider.defaultLayer),
     Layer.provide(Plugin.defaultLayer),
     Layer.provide(LLMClient.layer.pipe(Layer.provide(RequestExecutor.defaultLayer))),
+    Layer.provide(RuntimeFlags.defaultLayer),
   ),
 )
 
diff --git a/packages/opencode/src/session/llm/README.md b/packages/opencode/src/session/llm/README.md
index 2983c5ce24..b3081664b3 100644
--- a/packages/opencode/src/session/llm/README.md
+++ b/packages/opencode/src/session/llm/README.md
@@ -11,6 +11,6 @@ This folder contains adapters behind that service boundary:
 Safety boundary:
 
 - AI SDK remains the default.
-- `OPENCODE_LLM_RUNTIME=native` is an opt-in hint, not a global replacement.
+- `OPENCODE_EXPERIMENTAL_NATIVE_LLM=true` is an opt-in hint, not a global replacement. The legacy `OPENCODE_LLM_RUNTIME=native` env var is still accepted by `RuntimeFlags` for local testing.
 - Native execution currently runs only for OpenAI-compatible Responses models exposed through `@ai-sdk/openai`: direct `openai` API-key auth and console-managed `opencode`/Zen API-key config.
 - Unsupported providers, OpenAI OAuth, and missing API-key cases fall back to AI SDK.
diff --git a/packages/opencode/test/session/compaction.test.ts b/packages/opencode/test/session/compaction.test.ts
index 3c276d84dc..ea5e937166 100644
--- a/packages/opencode/test/session/compaction.test.ts
+++ b/packages/opencode/test/session/compaction.test.ts
@@ -1629,20 +1629,12 @@ describe("SessionNs.getUsage", () => {
     })
     const result = SessionNs.getUsage({
       model,
-      usage: {
+      usage: usage({
         inputTokens: 650_000,
         outputTokens: 100_000,
         totalTokens: 750_000,
-        inputTokenDetails: {
-          noCacheTokens: undefined,
-          cacheReadTokens: 100_000,
-          cacheWriteTokens: undefined,
-        },
-        outputTokenDetails: {
-          textTokens: undefined,
-          reasoningTokens: undefined,
-        },
-      },
+        cacheReadInputTokens: 100_000,
+      }),
     })
 
     expect(result.tokens.input).toBe(550_000)
@@ -1674,20 +1666,7 @@ describe("SessionNs.getUsage", () => {
     })
     const result = SessionNs.getUsage({
       model,
-      usage: {
-        inputTokens: 300_000,
-        outputTokens: 100_000,
-        totalTokens: 400_000,
-        inputTokenDetails: {
-          noCacheTokens: undefined,
-          cacheReadTokens: undefined,
-          cacheWriteTokens: undefined,
-        },
-        outputTokenDetails: {
-          textTokens: undefined,
-          reasoningTokens: undefined,
-        },
-      },
+      usage: usage({ inputTokens: 300_000, outputTokens: 100_000, totalTokens: 400_000 }),
     })
 
     expect(result.cost).toBe(0.9 + 0.4)
diff --git a/packages/opencode/test/session/llm-native-recorded.test.ts b/packages/opencode/test/session/llm-native-recorded.test.ts
index bc1297e5d1..2c845a654b 100644
--- a/packages/opencode/test/session/llm-native-recorded.test.ts
+++ b/packages/opencode/test/session/llm-native-recorded.test.ts
@@ -13,6 +13,7 @@ import { Provider } from "@/provider/provider"
 import { ModelID, ProviderID } from "@/provider/schema"
 import { Filesystem } from "@/util/filesystem"
 import { LLMClient, RequestExecutor } from "@opencode-ai/llm/route"
+import { RuntimeFlags } from "@/effect/runtime-flags"
 import type { Agent } from "../../src/agent/agent"
 import { LLM } from "../../src/session/llm"
 import { MessageV2 } from "../../src/session/message-v2"
@@ -127,6 +128,7 @@ function recordedNativeLLMLayer(cassette: string, metadata: Record<string, unkno
     Layer.provide(Plugin.defaultLayer),
     Layer.provide(client),
     Layer.provide(cassetteService),
+    Layer.provide(RuntimeFlags.layer({ experimentalNativeLlm: true })),
   )
 
   return Layer.mergeAll(providerLayer, llmLayer)
@@ -175,22 +177,6 @@ const collect = (input: LLM.StreamInput) =>
     return Array.from(yield* llm.stream(input).pipe(Stream.runCollect))
   })
 
-const nativeRuntime = <A, E, R>(effect: Effect.Effect<A, E, R>) => {
-  return Effect.acquireUseRelease(
-    Effect.sync(() => {
-      const previous = process.env.OPENCODE_LLM_RUNTIME
-      process.env.OPENCODE_LLM_RUNTIME = "native"
-      return previous
-    }),
-    () => effect,
-    (previous) =>
-      Effect.sync(() => {
-        if (previous === undefined) delete process.env.OPENCODE_LLM_RUNTIME
-        else process.env.OPENCODE_LLM_RUNTIME = previous
-      }),
-  )
-}
-
 describe("session.llm native recorded", () => {
   recordedOpenAIInstance("uses real RequestExecutor with HTTP recorder for native OpenAI tools", () =>
     Effect.gen(function* () {
@@ -210,34 +196,32 @@ describe("session.llm native recorded", () => {
       const resolved = yield* getModel(ProviderID.openai, ModelID.make(model.id))
       let executed: unknown
 
-      const events = yield* nativeRuntime(
-        collect({
-          user: {
-            id: MessageID.make("msg_user-recorded-native-tool"),
-            sessionID,
-            role: "user",
-            time: { created: 0 },
-            agent: agent.name,
-            model: { providerID: ProviderID.make("openai"), modelID: ModelID.make(model.id) },
-          } satisfies MessageV2.User,
+      const events = yield* collect({
+        user: {
+          id: MessageID.make("msg_user-recorded-native-tool"),
           sessionID,
-          model: resolved,
-          agent,
-          system: ["You must call the lookup tool exactly once with query weather. Do not answer in text."],
-          messages: [{ role: "user", content: "Use lookup." }],
-          toolChoice: "required",
-          tools: {
-            lookup: tool({
-              description: "Lookup data.",
-              inputSchema: z.object({ query: z.string() }),
-              execute: async (args, options) => {
-                executed = { args, toolCallId: options.toolCallId }
-                return { output: "looked up" }
-              },
-            }),
-          },
-        }),
-      )
+          role: "user",
+          time: { created: 0 },
+          agent: agent.name,
+          model: { providerID: ProviderID.make("openai"), modelID: ModelID.make(model.id) },
+        } satisfies MessageV2.User,
+        sessionID,
+        model: resolved,
+        agent,
+        system: ["You must call the lookup tool exactly once with query weather. Do not answer in text."],
+        messages: [{ role: "user", content: "Use lookup." }],
+        toolChoice: "required",
+        tools: {
+          lookup: tool({
+            description: "Lookup data.",
+            inputSchema: z.object({ query: z.string() }),
+            execute: async (args, options) => {
+              executed = { args, toolCallId: options.toolCallId }
+              return { output: "looked up" }
+            },
+          }),
+        },
+      })
 
       expect(events.filter((event) => event.type === "step-finish")).toHaveLength(1)
       expect(events.filter((event) => event.type === "finish")).toHaveLength(1)
@@ -263,34 +247,32 @@ describe("session.llm native recorded", () => {
       const resolved = yield* getModel(ProviderID.opencode, ModelID.make(model.id))
       let executed: unknown
 
-      const events = yield* nativeRuntime(
-        collect({
-          user: {
-            id: MessageID.make("msg_user-recorded-native-zen-tool"),
-            sessionID,
-            role: "user",
-            time: { created: 0 },
-            agent: agent.name,
-            model: { providerID: ProviderID.opencode, modelID: ModelID.make(model.id) },
-          } satisfies MessageV2.User,
+      const events = yield* collect({
+        user: {
+          id: MessageID.make("msg_user-recorded-native-zen-tool"),
           sessionID,
-          model: resolved,
-          agent,
-          system: ["You must call the lookup tool exactly once with query weather. Do not answer in text."],
-          messages: [{ role: "user", content: "Use lookup." }],
-          toolChoice: "required",
-          tools: {
-            lookup: tool({
-              description: "Lookup data.",
-              inputSchema: z.object({ query: z.string() }),
-              execute: async (args, options) => {
-                executed = { args, toolCallId: options.toolCallId }
-                return { output: "looked up" }
-              },
-            }),
-          },
-        }),
-      )
+          role: "user",
+          time: { created: 0 },
+          agent: agent.name,
+          model: { providerID: ProviderID.opencode, modelID: ModelID.make(model.id) },
+        } satisfies MessageV2.User,
+        sessionID,
+        model: resolved,
+        agent,
+        system: ["You must call the lookup tool exactly once with query weather. Do not answer in text."],
+        messages: [{ role: "user", content: "Use lookup." }],
+        toolChoice: "required",
+        tools: {
+          lookup: tool({
+            description: "Lookup data.",
+            inputSchema: z.object({ query: z.string() }),
+            execute: async (args, options) => {
+              executed = { args, toolCallId: options.toolCallId }
+              return { output: "looked up" }
+            },
+          }),
+        },
+      })
 
       expect(events.filter((event) => event.type === "step-finish")).toHaveLength(1)
       expect(events.filter((event) => event.type === "finish")).toHaveLength(1)
diff --git a/packages/opencode/test/session/llm.test.ts b/packages/opencode/test/session/llm.test.ts
index 6744362a71..d0dfd21e08 100644
--- a/packages/opencode/test/session/llm.test.ts
+++ b/packages/opencode/test/session/llm.test.ts
@@ -21,6 +21,7 @@ import type { Agent } from "../../src/agent/agent"
 import { MessageV2 } from "../../src/session/message-v2"
 import { SessionID, MessageID } from "../../src/session/schema"
 import { AppRuntime } from "../../src/effect/app-runtime"
+import { RuntimeFlags } from "@/effect/runtime-flags"
 
 const openAIConfig = (model: ModelsDev.Provider["models"][string], baseURL: string): Partial<Config.Info> => {
   const { experimental: _experimental, ...configModel } = model
@@ -66,13 +67,14 @@ async function drainWith(layer: Layer.Layer<LLM.Service>, input: LLM.StreamInput
   )
 }
 
-function llmLayerWithExecutor(executor: Layer.Layer<RequestExecutor.Service>) {
+function llmLayerWithExecutor(executor: Layer.Layer<RequestExecutor.Service>, flags: Partial<RuntimeFlags.Info> = {}) {
   return LLM.layer.pipe(
     Layer.provide(Auth.defaultLayer),
     Layer.provide(Config.defaultLayer),
     Layer.provide(Provider.defaultLayer),
     Layer.provide(Plugin.defaultLayer),
     Layer.provide(LLMClient.layer.pipe(Layer.provide(executor))),
+    Layer.provide(RuntimeFlags.layer(flags)),
   )
 }
 
@@ -769,39 +771,32 @@ describe("session.llm.stream", () => {
     await WithInstance.provide({
       directory: tmp.path,
       fn: async () => {
-        const previous = process.env.OPENCODE_LLM_RUNTIME
-        process.env.OPENCODE_LLM_RUNTIME = "native"
-        try {
-          const resolved = await getModel(ProviderID.openai, ModelID.make(model.id))
-          const sessionID = SessionID.make("session-test-native")
-          const agent = {
-            name: "test",
-            mode: "primary",
-            options: {},
-            permission: [{ permission: "*", pattern: "*", action: "allow" }],
-            temperature: 0.2,
-          } satisfies Agent.Info
+        const resolved = await getModel(ProviderID.openai, ModelID.make(model.id))
+        const sessionID = SessionID.make("session-test-native")
+        const agent = {
+          name: "test",
+          mode: "primary",
+          options: {},
+          permission: [{ permission: "*", pattern: "*", action: "allow" }],
+          temperature: 0.2,
+        } satisfies Agent.Info
 
-          await drain({
-            user: {
-              id: MessageID.make("msg_user-native"),
-              sessionID,
-              role: "user",
-              time: { created: Date.now() },
-              agent: agent.name,
-              model: { providerID: ProviderID.make("openai"), modelID: resolved.id, variant: "high" },
-            } satisfies MessageV2.User,
+        await drainWith(llmLayerWithExecutor(RequestExecutor.defaultLayer, { experimentalNativeLlm: true }), {
+          user: {
+            id: MessageID.make("msg_user-native"),
             sessionID,
-            model: resolved,
-            agent,
-            system: ["You are a helpful assistant."],
-            messages: [{ role: "user", content: "Hello" }],
-            tools: {},
-          })
-        } finally {
-          if (previous === undefined) delete process.env.OPENCODE_LLM_RUNTIME
-          else process.env.OPENCODE_LLM_RUNTIME = previous
-        }
+            role: "user",
+            time: { created: Date.now() },
+            agent: agent.name,
+            model: { providerID: ProviderID.make("openai"), modelID: resolved.id, variant: "high" },
+          } satisfies MessageV2.User,
+          sessionID,
+          model: resolved,
+          agent,
+          system: ["You are a helpful assistant."],
+          messages: [{ role: "user", content: "Hello" }],
+          tools: {},
+        })
 
         const capture = await request
         expect(capture.url.pathname.endsWith("/responses")).toBe(true)
@@ -862,47 +857,40 @@ describe("session.llm.stream", () => {
     await WithInstance.provide({
       directory: tmp.path,
       fn: async () => {
-        const previous = process.env.OPENCODE_LLM_RUNTIME
-        process.env.OPENCODE_LLM_RUNTIME = "native"
-        try {
-          const resolved = await getModel(ProviderID.openai, ModelID.make(model.id))
-          const sessionID = SessionID.make("session-test-native-injected-tool")
-          const agent = {
-            name: "test",
-            mode: "primary",
-            options: {},
-            permission: [{ permission: "*", pattern: "*", action: "allow" }],
-          } satisfies Agent.Info
+        const resolved = await getModel(ProviderID.openai, ModelID.make(model.id))
+        const sessionID = SessionID.make("session-test-native-injected-tool")
+        const agent = {
+          name: "test",
+          mode: "primary",
+          options: {},
+          permission: [{ permission: "*", pattern: "*", action: "allow" }],
+        } satisfies Agent.Info
 
-          await drainWith(llmLayerWithExecutor(executor), {
-            user: {
-              id: MessageID.make("msg_user-native-injected-tool"),
-              sessionID,
-              role: "user",
-              time: { created: Date.now() },
-              agent: agent.name,
-              model: { providerID: ProviderID.make("openai"), modelID: resolved.id },
-            } satisfies MessageV2.User,
+        await drainWith(llmLayerWithExecutor(executor, { experimentalNativeLlm: true }), {
+          user: {
+            id: MessageID.make("msg_user-native-injected-tool"),
             sessionID,
-            model: resolved,
-            agent,
-            system: [],
-            messages: [{ role: "user", content: "Use lookup" }],
-            tools: {
-              lookup: tool({
-                description: "Lookup data",
-                inputSchema: z.object({ query: z.string() }),
-                execute: async (args, options) => {
-                  executed = { args, toolCallId: options.toolCallId }
-                  return { output: "looked up" }
-                },
-              }),
-            },
-          })
-        } finally {
-          if (previous === undefined) delete process.env.OPENCODE_LLM_RUNTIME
-          else process.env.OPENCODE_LLM_RUNTIME = previous
-        }
+            role: "user",
+            time: { created: Date.now() },
+            agent: agent.name,
+            model: { providerID: ProviderID.make("openai"), modelID: resolved.id },
+          } satisfies MessageV2.User,
+          sessionID,
+          model: resolved,
+          agent,
+          system: [],
+          messages: [{ role: "user", content: "Use lookup" }],
+          tools: {
+            lookup: tool({
+              description: "Lookup data",
+              inputSchema: z.object({ query: z.string() }),
+              execute: async (args, options) => {
+                executed = { args, toolCallId: options.toolCallId }
+                return { output: "looked up" }
+              },
+            }),
+          },
+        })
 
         expect(captured?.model).toBe(model.id)
         expect(captured?.tools).toEqual([
@@ -990,47 +978,40 @@ describe("session.llm.stream", () => {
     await WithInstance.provide({
       directory: tmp.path,
       fn: async () => {
-        const previous = process.env.OPENCODE_LLM_RUNTIME
-        process.env.OPENCODE_LLM_RUNTIME = "native"
-        try {
-          const resolved = await getModel(ProviderID.openai, ModelID.make(model.id))
-          const sessionID = SessionID.make("session-test-native-tool")
-          const agent = {
-            name: "test",
-            mode: "primary",
-            options: {},
-            permission: [{ permission: "*", pattern: "*", action: "allow" }],
-          } satisfies Agent.Info
+        const resolved = await getModel(ProviderID.openai, ModelID.make(model.id))
+        const sessionID = SessionID.make("session-test-native-tool")
+        const agent = {
+          name: "test",
+          mode: "primary",
+          options: {},
+          permission: [{ permission: "*", pattern: "*", action: "allow" }],
+        } satisfies Agent.Info
 
-          await drain({
-            user: {
-              id: MessageID.make("msg_user-native-tool"),
-              sessionID,
-              role: "user",
-              time: { created: Date.now() },
-              agent: agent.name,
-              model: { providerID: ProviderID.make("openai"), modelID: resolved.id },
-            } satisfies MessageV2.User,
+        await drainWith(llmLayerWithExecutor(RequestExecutor.defaultLayer, { experimentalNativeLlm: true }), {
+          user: {
+            id: MessageID.make("msg_user-native-tool"),
             sessionID,
-            model: resolved,
-            agent,
-            system: [],
-            messages: [{ role: "user", content: "Use lookup" }],
-            tools: {
-              lookup: tool({
-                description: "Lookup data",
-                inputSchema: z.object({ query: z.string() }),
-                execute: async (args, options) => {
-                  executed = { args, toolCallId: options.toolCallId }
-                  return { output: "looked up" }
-                },
-              }),
-            },
-          })
-        } finally {
-          if (previous === undefined) delete process.env.OPENCODE_LLM_RUNTIME
-          else process.env.OPENCODE_LLM_RUNTIME = previous
-        }
+            role: "user",
+            time: { created: Date.now() },
+            agent: agent.name,
+            model: { providerID: ProviderID.make("openai"), modelID: resolved.id },
+          } satisfies MessageV2.User,
+          sessionID,
+          model: resolved,
+          agent,
+          system: [],
+          messages: [{ role: "user", content: "Use lookup" }],
+          tools: {
+            lookup: tool({
+              description: "Lookup data",
+              inputSchema: z.object({ query: z.string() }),
+              execute: async (args, options) => {
+                executed = { args, toolCallId: options.toolCallId }
+                return { output: "looked up" }
+              },
+            }),
+          },
+        })
 
         const capture = await request
         expect(capture.body.tools).toEqual([